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All About Torches By Dr David Maddison Illumination so we can be active beyond daylight hours has always been an important technology. On foot, that usually means a torch. Once a stick with a fire on the end, modern torches (known elsewhere as “flashlights”) are almost always batterypowered. Image source: https://unsplash.com/photos/YK8Mvocj6yE P can also be gas or liquid-fuelled lanterns, or even chemical “glow sticks” that use chemiluminescence to create light. But this article will focus on electric torches. Until the introduction of LEDs, torches mainly used incandescent bulbs. Various types were available, described below. Batteries used were typically based on carbon-zinc 1.5V cells or, in later times, alkaline cells or nicad/NiMH rechargeables. By the time lithium-ion rechargeable batteries became commonly available, LEDs were the dominant lighting source. Some LED torches support multi-voltage operation, for example, being powered by a single AA alkaline cell at 1.5V or a 3.7V Li-ion rechargeable 14500 (same size as AA) cell. But that only works if the torch electronics are designed to handle the wide range of voltages. ortable lights Origin of the term “flashlight” In the UK and its former colonies, we use the term “torch”, but in the USA and Canada, the term is 14 Silicon Chip “flashlight”. The word “flash-light” predates the invention of battery-­ powered devices. It appeared in 1892 but referred to flash photography, where the flash came from chemicals. The Flashlight Museum (www. wordcraft.net/flashlight.html) says that the origin relates to early torches that had weak carbon-filament lamps and weak, low-powered cells with no switch to keep them on permanently, as extended operation would quickly drain the cells. The cells needed to ‘recover’ between uses. Electrical contact was made by pressing a spring-loaded contact to Fig.1: an “Ever Ready” flashlight from 1899. Note the momentary switch in the middle, hence “flashlight”. complete the circuit; hence, the light would flash. The first torch As we noted in our article All About Batteries (January 2022; siliconchip. com.au/Series/375), the D cell was invented in 1896 (and it’s still available today!). It was a dry cell; as there were no liquids to spill, it was suitable for portable use in any orientation. While not the first dry cell, it was the first that was mass-produced and led to the torch’s development. The first torch patent was assigned to British inventor David Missell who obtained US Patent 617,592 in 1899 (https://patents.google.com/patent/ US617592A/en and Figs.1 & 2). It used three D cells in a cardboard tube with a brass reflector and a carbon filament bulb. Some were donated to the New York City police, who liked them, but the torch was not generally popular because the batteries had a low capacity and the carbon filament bulb was not efficient or bright. At the time, torches were considered an expensive novelty. siliconchip.com.au Torches did not become popular until the development of the tungsten filament bulb (three times the efficiency of a carbon filament) in 1904 and the development of better batteries. By 1922, there were an estimated 10 million torch users in the United States. A range of devices was available, including tubular designs, lantern styles that could be set down, small pocket-size devices and large lights suitable for long-range use – see Fig.2. The first LED torch Who made the first LED torch is discussed in detail at siliconchip.au/link/ abfm – in summary: • Rockwell gave out promotional LED torches in the late 1970s to early 1980s • Edmund Scientific made a yellow LED torch in the late 1970s • Tekna made a red LED torch around 1980 • HDS Systems in Tucson, Arizona, USA made a torch with multiple LEDs in 1997 or 1998. • Arc Flashlight LLC (website – www.arcflashlight.com) was the first to sell high-power Luxeon Star LED torches around 2001 with the Arc LS model (see Fig.3). It was the first LED torch to rival incandescent torches. The company was in business from 2001 to 2004. Torch configurations The key elements of a torch are: 1) a light source and, if applicable, a reflector, lens and heatsink 2) driving electronics if the torch is not a direct-drive type 3) a battery 4) a switch Various other hardware is associated with the entire torch assembly, such as o-rings, clips, etc. Apart from the archetypal handheld model, traditionally about the diameter of a D cell, there are (continued overleaf): Fig.3: the first commercial LED torch (the Arc LS) that was competetive with incandescent torches. siliconchip.com.au Fig.2: early torches from the 25th MESCO (Manhattan Electrical Supply Co) catalog, circa 1910. Personal recollections on torches One of my earliest recollections of torches was my father walking me to a Cub Scout meeting through a dark park with a 3LR12 4.5V-battery powered light (see photo). They were often used on bicycles at the time but were easily removable for general use. Another time, I ascended Mt Bogong in Victoria and arrived at the campsite at night. I had decent lighting, but my walking companion had an inadequate incandescent torch powered by two AA cells which seemed nearly flat. That taught me several lessons: the importance of having at least one form of backup lighting and spare batteries when in the bush, and the extreme difficulty of setting up camp on a dark night without adequate lighting. Fortunately, having sufficient A vintage bicycle torch powered by lighting is rarely a problem these days a 3LR12 4.5V battery. By today’s with the ready availability, low cost, standards, the light was dim and low weight and high performance of battery life short, but they were still popular, especially for bicycles. LED lights. Australia's electronics magazine November 2022  15 • headlamps for applications such as caving or working hands-free • ‘lanterns’ designed to sit on a flat surface or hang from something to illuminate an area • torches with different light colours such as red to preserve night vision function for the military, hunters or astronomers • keychain lights • hand-cranked torches with a built-in generator for emergency applications • firearm mounted lights for hunters, law enforcement or the military • torches for scuba diving • lights for hazardous areas such as mines that are designed not to be an ignition source • inspection lights, with the light on a flexible mounting • infrared torches for use with night vision equipment • ‘shaker lights’, novelty items that produce light when shaken via a moving magnet (some are fake and have internal batteries) Apart from all those, most modern phones have a torch function. Light Sources In addition to incandescent globes and LEDs, there are other light sources such as HID lamps (high-­intensity discharge, less common now due to the availability of high-power LEDs) and the emerging technology of “laser” torches that use an LEP or laser-­ excited phosphor (siliconchip.au/ link/abfn). Incandescent bulbs Incandescent torch bulbs are mostly obsolete now but are still available. They are mainly defined by their Fig.4: a P13.5S base torch bulb, in this case, a Satco S6923 (0.63W, 2.33V). It has a “B3 1/2” shape, a C2-R filament and a rated life of 10 hours. 16 Silicon Chip Battery Warnings Lithium-ion batteries contain a lot of energy and can be hazardous. Also, keep button and coin cells away from children and animals as they are hazardous if swallowed. voltage rating, power rating, base configuration, glass bulb shape, gas filling and whether they flash (rare). Some bulbs are manufactured with LEDs as direct replacements for conventional incandescent globes. Incandescent bulbs can be small, or large sealed-beam units as used on older-style car headlights (eg, as used in the Big Jim torches, described later). Some higher-performance bulbs are filled with xenon or krypton gas, reducing the tendency of the tungsten filament to evaporate and allowing it to run at a higher temperature, making it brighter and more efficient. Halogen globes are filled with inert gas and a halogen substance such as iodine or bromine. A chemical reaction causes evaporated tungsten to be redeposited on the filament. Incandescent bulbs and LED bulbs that replace them (when made) are available in various base types. For each base type, various voltage and power ranges are available. Some common types include: ANSI P13.5S Also known as single contact (SC) miniature flange base (see Fig.4), this bulb has a flange with a maximum diameter of 13.5mm. The maximum distance from the base contact to the top of the metal barrel is 14mm. It is a common bulb for older torches. E10 This is also known as Miniature Edison Screw (MES). Fig.5: a G1.27 miniature bulb (1.27mm pin spacing). This 42005 bulb (1.35V, 0.32A) has a T-1 shape as used in AAA Maglites. Source: www.topbulb. com Australia's electronics magazine BA9S This base type is commonly used for older vehicle indicators but also by some torches and LED replacement bulbs. Miniature globes, eg, G1.27 base This bulb (Fig.5) has two pins protruding from the base. The number after the G indicates the centre-to-­ centre spacing between the pins in millimetres. Blinking bulb There were once bulbs that blinked, driven via a bimetallic strip inside the globe, which alternately heated and cooled, making and breaking electrical contact (Fig.6). They were available for 1.5V, 2.5V, 3.5V or 6V operation and were used in numerous toys in the 1960s as well as the Big Jim torch (see below) and even pinball machines. The base was typically an E10 and the current draw was 200mA with a 1Hz flash rate and 50% duty cycle – see siliconchip.au/link/abfo Fluorescent tubes Some torches use a miniature fluorescent tube – see Fig.7. They used to be somewhat common but are now rare as LED globes are superior. This style of torch remains in a specialised form to create UV or ‘black light’ to cause fluorescence in certain items such as currency, minerals, watermarks, biological contamination etc. Fig.6: a flashing globe from an old pinball machine with a BA9S base. Source: www.pinball.center siliconchip.com.au Fig.8: construction of a typical 3mm or 5mm LED as used in basic torches. LEDs LEDs (Figs.8-10) tend not to be removable like incandescent globes as they do not need routine replacement and are often an integral part of the torch. However, enthusiasts do change them for different types, power ratings, colour temperature tint or other desired characteristics. There are slight variations in LEDs coming from the same production line, so all LEDs are tested and ‘binned’ into types with similar characteristics, much like other semiconductors. Major LED manufacturers for torches are Cree, Luminus, Nichia, Osram, Philips Lumileds (Luxeon), Samsung and Seoul Semiconductor. LED emitters typically have no markings, so you have to know what they are or identify them from a chart such as at https://flashlightwiki.com/ LED_Gallery High-end LEDs used in torches typically have an efficiency of around 100lm/W (lumens per watt). Fig.9: a Cree XM-L2 T6 3B emitter attached to an MCPCB (metal core printed circuit board), used for the torch build described in the text. Fig.11: a 35W HID lamp (Philips CDM35/T6/830) with a two-pin G12 base, producing 3100 lumens. It is 103mm long and 20mm in diameter. The bases can be purchased without emitters to attach your own, or with the emitter already attached. runaway heating, so the current has to be limited using a ballast or other electronics. HID torches are still available but tend to be more expensive than others, and current high-power LED technology is competitive with them. High-intensity discharge lamps HID lamps work by establishing an electrical arc between two tungsten electrodes inside a quartz or alumina tube. The tube is filled with an inert gas (argon, neon, krypton and/or xenon) and a suitable metal or metal salts (eg, mercury, sodium or halides) – see Fig.11. When an arc is struck, the high-­ temperature plasma (ionised gas) generated causes the metal or salts to evaporate. Within any metal or metal salt at a high temperature, electrons jump between energy states, resulting in light generation. The light usually includes UV, which is filtered out. HID lamps are much more efficient than incandescent lamps but are more expensive due to the need for fairly complex control electronics. They have a negative resistance temperature coefficient, which could lead to A Phoebus Horizon HID 35W searchlight (shown below) with 3500 lumen intensity, 1370m throw and 2.5h runtime. Laser-excited phosphor (LEP) In an LEP torch, a blue laser beam is directed onto a special phosphor coating adhered to a metal plate (see Figs.12-14 and https://youtu. be/G0V3p8cc-3I). The laser causes the phosphor to fluoresce, emitting Fig.7: a UV torch with a fluorescent tube. Such ‘black lights’ have various scientific and law enforcement uses. Fig.10: how a LED emitter is attached to an MCPCB. siliconchip.com.au Australia's electronics magazine November 2022  17 broad-spectrum white light. The light emitted is not a laser beam but is laser-like. Classic laser light is monochromatic or close to it; the light from an LEP torch contains all colours. Note that ‘phosphor’ does not necessarily refer to the chemical element phosphorous but any substance that emits light when exposed to radiant energy. Typically, the blue light from the laser shines onto an yttrium aluminium garnet (YAG) phosphor, which absorbs the blue light and re-emits it as a combination of colours, making a white beam. This is similar to how white LEDs function; a blue or UV LED emits light onto a phosphor mix which re-emits it as white. The beam from an LEP torch is pencil-­like and the torch is very efficient. A blue laser is used because it is easier and more efficient for blue light to excite phosphors to produce the desired range of colours in the visible spectrum than other colours such as red or green. BMW uses LEP headlights in many of its vehicles, including the X7. The lights use less power, have longer range and enable a smaller headlight housing than LED lights. You can view a teardown and repair video on YouTube for a BMW laser headlight titled “Laser Headlight Teardown and How Fig.12: how a laser-enhanced phosphor (LEP) torch works. to Repair color change” at https:// youtu.be/a5mAdDl5pTA Power sources Power usually comes from a battery (rechargeable or disposable), which might be recharged via a solar panel or hand crank for emergencies (only some types). Supercapacitor-powered torches are sometimes seen. They don’t have the runtime of batteries but they can be charged very rapidly. You can easily make your own, and there are many online instructions; search the web for “supercapacitor torch”. You can find two examples at siliconchip.au/ link/abfp and siliconchip.au/link/abfq Consider that some rechargeable cells, such as certain protected 18650s, are too long to fit in some Fig.13: the Weltool W4Pro, an LEP torch. On high, it produces 560lm with a 2670m throw and two hour runtime. torch compartments. In this case, a non-­protected cell must be used, but make sure the torch has low-voltage shutdown to protect the cell. Also, some 18650s have flat tops that won’t make a good (or any) connection with the torch contacts. In that case, use button-top cells if they fit. LED drivers Most LED torches are not ‘direct drive’ and include an electronic driver to regulate the current and/or voltage delivered to the LED. The electronics might also provide multiple modes (eg, low/medium/high brightness), monitor the battery voltage and LED temperature, protect against reversed battery polarity, manage charging and possibly other tasks. Fig.14: a W4Pro beamshot. The narrow, pencil-look beam is typical of LEP torches. Fig.15: current vs voltage for differently-coloured low-power LEDs. The steep increase in current with voltage indicates why current regulation is preferred. 18 Silicon Chip ► Australia's electronics magazine siliconchip.com.au Fig.16: one of the simplest possible LED torch circuits. Each type of LED has a maximum current and power rating. The voltage across the LED (Vf or forward voltage) varies depending on the colour and type. UV LEDs have the highest Vf at 3.1-4.4V; violet 2.8-4.0V; blue 2.5-3.7V; green 1.9-4.0V; yellow 2.12.2V; orange/amber 2.0-2.1V; red 1.62.0V; infrared 1.2-1.7V. White LEDs typically require around 3.0-3.6V (see Fig.15). LEDs are generally not driven with a fixed voltage because the current increases exponentially with voltage once Vf is exceeded, and they could experience thermal runaway. There are several ways to regulate LED power. These include direct drive, a linear regulator, pulse width modulation (PWM), boost or buck circuits, or a combination boost/buck circuit to drive the LED at the correct voltage, regardless of the input voltage. One of the simplest LED torch circuits is shown in Fig.16. It is a battery, LED and a resistor to limit the LED voltage and current. Direct drive In direct drive circuits, the voltage of the battery or power supply has to be no greater than the maximum Vf of the LED. They usually rely on the battery’s internal resistance or power supply to limit the maximum LED power. This is not an advanced method, but it can work. Fig.17: eight AMC7135 regulators plus a microcontroller fit on this small PCB to provide up to 3.04A (note that some AMC7135s are rated at 380mA rather than 350mA). The micro provides 12 group modes; this board was used for the torch build described in the panel at the end of the article. Taking Jaycar Cat ZD0196 as an example, Vf(typical) = 3.2V and Imax = 100mA. To drive that LED from a 9V battery, you could use a resistor of R = (9V – 3.2V) ÷ 0.1A = 58W (round up to 62W to be safe). That assumes Vf(min) is close to Vf(typical). For more on driving LEDs directly, including combinations of LEDs, see: • siliconchip.au/link/abfr • siliconchip.au/link/abfs • electronicsclub.info/leds.htm You can have fun buying a bag of 3mm or 5mm LEDs and a solderless breadboard and try connecting the LEDs in various series/parallel combinations. See the online calculator at siliconchip.au/link/abft The different series/parallel combinations give different voltages and currents for driving the same LEDs (the product of these, ie, the power will be mostly constant). For more information on this, see: • siliconchip.au/link/abfu • siliconchip.au/link/abfv Linear regulation The term linear regulator might refer Resistor current limiting The current to the LED can be limited using a series resistor, although the LED will dim as the battery discharges, and the resistor can dissipate a fair bit of power. If Vs(max) is the maximum supply voltage, Imax is the LED’s maximum current and Vf(min) is the minimum Vf at Imax, the resistor value required can be calculated as R = (Vs(max) − Vf(min)) ÷ Imax. siliconchip.com.au to either current or voltage regulation. Typically, LEDs are driven with a constant current. If the voltage supplied to the regulator is higher than Vf, energy is lost as heat. If the voltage drops below Vf, the current will be less than intended, but losses will be low. It is ideal to supply the regulator with as close to Vf as possible. A common current-regulating chip used in torches is the AMC7135 which can handle up to 350mA. Up to four can be placed on each side of a 17mm diameter driver board to give a total of 2.8A, which suits LEDs like the XP-L and XM-L2 in torches using 18650 Li-ion batteries (18mm diameter, 65mm long) – see Fig.17. A microcontroller can be combined with the linear regulator(s) to control brightness using PWM (see Fig.18). PWM (typically using a Mosfet) Instead of using a linear regulator, a Mosfet (or BJT) can be switched on and off by a microcontroller to control brightness using PWM as described above. The Mosfet acts as a low-­ resistance on/off switch. There is little voltage across the Mosfet when on, so it dissipates very little power. Some sort of current limiting is usually required. Still, it can be arranged to dissipate less power by operating it at a reduced duty cycle to achieve maximum brightness, so the overall efficiency is improved. Boost or buck circuit Fig.18: how PWM is used to vary duty cycle and thus control average current. Australia's electronics magazine An LED can be driven by either a boost or buck circuit that increases or decreases the supply voltage to that most appropriate for the LED. Some circuits can either boost or buck. These circuits are most efficient when the input voltage is close to the output drive voltage, but they are usually much more efficient than linear regulation regardless. November 2022  19 Fig.19: a flow chart for the generic Andúril 2 torch firmware – this is the ‘simple’ section! Source: https:// budgetlightforum. com/node/76941 Driver firmware Believe it or not, there are operating systems for torches (see Fig.19). Drivers with microcontrollers require firmware and such software can even be written or modified by the enthusiast. The firmware controls the user interface, eg, the program will advance the brightness every time the on-off button is quickly clicked. Popular firmwares include A6, Andúril, Biscotti, Bistro, Crescendo, NarsilMulti and RampingIOS. For a lot more information and links for flashing tools and software, see siliconchip. au/link/abfx There is a repository of flashlight firmware at siliconchip.au/link/abfy if you are interested in seeing what it looks like or developing your own. There is also extensive documentation for Andúril at siliconchip.au/link/abfz Example code for the Convoy S2+ torch is at siliconchip.au/link/abg0 Torches of note example is: siliconchip.au/link/abg1 We are aware of at least one modern torch that uses this battery. Unusually, it also uses a traditional incandescent globe. Big Jim The Big Jim torch was a large light from the 1960s and possibly earlier (there is very little documented history on these torches). It used a sealed beam headlamp, much like some former car headlights. It was made by Union Carbide or Eveready and used a large (125.4 × 132.5 × 73mm) 6V ANSI 918 battery, IEC 4R25-2, with a capacity of around 18Ah for zinc chloride (RS Pro) models to 33Ah for alkaline (Varta). Within these were 8 F-size cells. If buying one of these batteries, note there is a similar ► For a comprehensive list of LED drivers, see siliconchip.au/link/abfw 12V battery, Rayovac model 926D or ANSI 926 equivalent. Big Jim came in a variety of models. Some had just the sealed beam main light, while others also had a flashing red light, using a bi-metal strip as described earlier. Torches in this style are still available from the Big Beam Company near Chicago, USA – see siliconchip.au/ link/abg2 One of that company’s torches from the 1950s, the Big Beam No. 164, is remarkably similar to the Union Carbide Big Jim from my collection (see Figs.21 & 22). This light was subject to US Patent 2,861,174 of 1958 by Big Beam, so we assume Union Carbide licensed the design. For further information on this, see siliconchip. au/link/abg3 Fig.20: the Varta Palm Light is a modern European torch that uses a 3LR12 battery. It has a 3.5h battery life, a throw of 75m and 15lm brightness. It is a rare example of a modern torch with an incandescent globe. Source: www. varta-ag.com/en/consumer/product-categories/ lights/palm-light Some of the more prominent torches throughout history are listed below: The 3LR12 battery was (and is) more common in Europe and Russia than in other countries. Some torches still use this battery – see Fig.20. Adaptors are available for purchase or 3D printing to enable three AA cells to be used instead of a 3LR12 battery. One 20 Silicon Chip ► 3LR12 torches Fig.21: a Big Beam No. 164 from the 1950s. Source: Made in Chicago Museum Australia's electronics magazine siliconchip.com.au Fig.24: the current Dolphin LED torch. Fig.23: the author’s Convoy S2 torches. The one on the left has 365nm UV LEDs and 1.05A driver. In the middle is an S2+ with an SST20 4000K LED and 2.8A driver; on the right is an S2+ with SST40 5000K LED and 3.05A driver. was waterproof and could float, but This battery (IEC 4R25X or 4LR25X) Convoy S2+ it found acceptance in many applica- has spring terminals and typically The Convoy S2 and the later version, tions beyond boating. contains four F-size cells. Typical batthe S2+ are popular and inexpensive The Dolphin MK1 was known in the tery capacities are 8.5Ah for a Varta torches for buying, modifying or even USA as the “All American” or “No. “431” Zn-MnO2 (Zinc Chloride) type building from parts (described later) – 108”. The MK1 is the only one with or 11.9Ah for a Varta “4430” alkaline see Fig.23. They are not a ‘big brand’ metal retaining clips for the lens bezel type. Typical dimensions are 115mm but have better quality than their price in the Dolphin model range. × 68.31m × 68.31m. would suggest and many favourable The Dolphin used a 6V lantern batThere is a bit of confusion about the reviews. If buying one, make sure it is tery which gave it a good run time by date of the MK1 Dolphin. The Austrafrom a reputable seller and not a fake standards of the day, as typical torches lian Museum of Applied Arts & Sci(see the panel on page 27). from then ran from two D cells (3V). ences website (siliconchip.au/link/ That was before alkaline cells were abg4) lists the design date as 1965. The Eveready Dolphin torch widely available; standard cells of the However, Eveready (siliconchip.au/ Almost all Australians will be famil- time had poor capacity and current link/abg5) has design and manufaciar with the iconic Eveready Dolphin delivery. The Dolphin had a bright and ture dates of 1966. It also states that torch (Fig.24). It started life in the ‘throwy’ (long range) beam compared Dolphin torches “have been lighting USA in 1965 and was produced for to other torches. up the lives of Australian & New Zeasale around the world. Having a large battery back then land families since 1967, when the first The Dolphin was initially designed (the 1960s and early 1970s) was the MK1 lantern was launched”. for the boating community and thus only way to get a reasonable capacity. The second generation of the torch, Fig.22: the author’s collection of three Big Jim torches. The left-hand torch (model 100) is very similar to the Big Beam; the middle torch (model 101) lacks the red flashing light, while the one with the plastic head (model 101C) is Australian-made. siliconchip.com.au Australia's electronics magazine Two hand-cranked torches. The smaller Chinese-made one has a LED, while the larger one is incandescent and believed to be of Soviet origin. November 2022  21 Fig.25: a modern LED Maglite Solitaire, originally released with a G1.27 incandescent bulb. Source: https://maglite.com Fig.26: the base model PakLite torch on top of a 9V battery. Several other models are also available. Fig.27: the Photon Micro-Light II LED keychain torch. It is powered by a CR2032 coin cell, or two stacked CR2016s. the MK2, was a project of Eveready Australia. Eveready contracted the design to Paul Cockburn of Design Field Pty Ltd in 1972. It became the best-selling torch in the world in the 1970s and was manufactured by Eveready worldwide in various locations. The MK2 dispensed with the metal clips of the MK1 and featured a more streamlined look. The MK3 was released in 1988, according to www. dolphintorches.com/about/, but the Powerhouse Museum (siliconchip. au/link/abg6) states that the MK3 was designed by Paul Cockburn in 1989. The MK3 bezel screws on rather than clipping on. The MK4 was introduced in 1996, followed by the MK4.2 in 2000 and the MK5 in 2003, which featured a new reflector design, integral rubber mouldings for impact protection around the lens, an adjustable stand and better ergonomics. According to the Powerhouse Museum, the MK4 and MK5 were designed by “Design Resource in Crows Nest, NSW for the US-based Energizer company” (Energizer Holdings is a division of Eveready). The MK6 was released in 2007 and then the MK7 LED in 2012, the first Dolphin featuring an LED. Eveready states that 20 million Dolphins have been sold in Australia and New Zealand over 45 years (1967 to 2012). In 2016, a new LED Dolphin was introduced, which has no “MK” designation but is stated to have 200 lumens output, a beam throw of 250m and a battery life of 65h. above. In 2012, the LED version of the Solitaire was introduced, but there are DIY and commercial LED conversions for the earlier version. It is significant because it was a well-engineered miniature keychain light. Although the incandescent version was not particularly bright, it was enough to find a keyhole at night. Maglite Solitaire AAA The 1988 Maglite Solitaire AAA battery model (Fig.25) uses one of the smallest, if not the smallest incandescent globe to go into a commercial torch; see the G1.27 bulb section PakLite This novel torch (see Fig.26 and https://paklitegear.com/) sits on top of a 9V battery. It is produced by a family living off-grid in the mountains of Oregon. It is characterised by light weight, useful light output and extreme run time of up to 1200+ hours with a lithium battery on low, 80+ hours on high or 600+/30+ hours for regular alkaline batteries. It can even run on ‘exhausted’ 9V batteries from sources like smoke detectors, as it can run down to a very low voltage. There are many imitations of this light. Photon Micro-Light Fig.28: a classic Maglite six D-cell incandescent xenon torch. Maglite still sells these. It has a beam distance of 338m, 178 lumens and 28547cd peak intensity. It is 485mm long and weighs 1417g with a battery. Source: https://maglite.com This light (see Fig.27) is an extremely small key chain light with a stated minimum 4.5 lumens output and 18h run time, weighing 6.27. Depending upon which beam colour is chosen, it uses either two CR2016 or one CR2032 cell. Surefire P60 and other P60 hosts Fig.29: two Surefire-style torches and a selection of P6-modules, some Surefire, others after-market; some incandescent, others LED. Source: author’s collection 22 Silicon Chip Australia's electronics magazine Surefire introduced their 6 Series torches in 1988 (Fig.29). The 6C model produced 60 lumens from two CR123 batteries and was smaller and brighter than any comparable torch at the time. The 6P and 6R models were released in 1989 and featured a P60 incandescent xenon light ‘drop-in’ module of 65 lumens or a P61 module of 120 lumens. Today, many different P60-style modules with different light options are available for various Surefire 6 series style “host” lights. Examples siliconchip.com.au include the UltraFire WF501B, WF502B, WF503B, WF504B, WF502D (http://flashlightwiki.com/UltraFire) & Solarforce L2 (http://flashlightwiki. com/Solarforce). UltraTac K18 I use this outstanding AAA/10440 cell torch daily (see siliconchip.au/ link/abg7 and Fig.30). 10440 refers to a rechargeable Li-ion cell in AAA format. Fig.30: the UltraTac K18 AAA torch. It has a maximum brightness of up to 370 lumens (with a 10440 Li-ion cell) and a maximum run time of 40h at low brightness. Upgrading a vintage torch You can bring new life to a vintage or antique torch (100+ years). Some people make permanent modifications by adding LEDs and new battery systems, but this is regarded as unacceptable by some for rare lights. It’s possible to make non-­permanent modifications, such as changing the incandescent bulb for a ‘drop-in’ direct replacement, which can be readily purchased for most incandescent bulb types (see Fig.31). Battery replacements can be made with adaptors, given the lower battery capacity required for driving LEDs. For example, you can replace a D cell with an adaptor containing one, two or three AA cells. Fig.31: the author replaced the incandescent bulb in this vintage torch with a LED and replaced the D cells with AAs in adaptors. Performance standards for torches The ANSI/NEMA FL-1 standard is used for rating torches. It provides standard ways to measure light output, runtime, peak beam intensity, beam distance, water resistance and impact resistance. Measurement of light output Lumens (lm), lux (lx) and candela (cd) are the three most common units used to characterise lighting sources, although there are others – see Fig.32. Torch enthusiasts and manufacturers frequently wish to characterise torches in terms of overall light output or luminous flux, typically measured in lumens. Unlike lumens, which measures overall light output, lux takes into account the area over which luminous flux is distributed and is a measure of illuminance. Lux is lumens per square meter. Ten lumens over an area of one square meter would be ten lux, but ten lumens over ten square meters would be one lux. Foot-candle is the obsolete non-SI equivalent unit and is 1lm per square foot. siliconchip.com.au Fig.32: how candela, lumen and lux are measured. Lumens is the most critical measurement for torches. Australia's electronics magazine November 2022  23 Useful Links • Flashlight Museum: www.wordcraft.net/flashlight.html • TPAD Direct Thermal Path Technology for LEDs on MCPCBs for more efficient heat removal: www.cutter.com.au/tpad/ • MCPCBs for sale: https://led-mounting-bases.com/en/310-led-mcpcb • BudgetLightForum: https://budgetlightforum.com/ • Candle Power Forums: www.candlepowerforums.com • Flashlight Wiki: https://flashlightwiki.com/Main_Page Useful Videos • “Post Vietnam War Flashlight – History” https://youtu.be/UiTGRa6EikE • “1930s Flashlight Restoration-Niagara Searchlight – Kipkay Restored” https://youtu.be/VHlVQMbdayw • “I Bought EVERY Flashlight at Home Depot!” https://youtu.be/bdjHhVhUOWY • “Flashlight Museum is an illuminating experience (2005)” https://youtu.be/XdigO6-1MEY (sadly, it appears to have closed) The candela is a measure of luminous intensity and quantifies the perceived power per unit solid angle emitted by a point light source in a particular direction. It is a weighted measurement that takes into account the sensitivity of the human eye to various wavelengths (called the luminosity function). A beam from a 1lm light source distributed evenly within one steradian (the 3D equivalent to the 2D radian unit of angular measurement) has a luminous intensity of one candela. If the same beam were evenly focused into half a steradian, the luminous intensity would be 2cd. A typical wax candle measures around 1cd. ‘Candlepower’ is an obsolete term, but today is considered equivalent to the candela. Sometimes, a torch will be advertised with a candlepower rating in the millions (which sounds impressive) because it has a tightly focused beam, but its overall output in lumens might be low. Throw is a measurement of how far away a torch can usefully light up an area and can be calculated from its candela rating – see siliconchip.au/link/ abg8 and siliconchip.au/link/abg9 Measuring a torch’s brightness The most important measurement related to torches is lumens, which can be measured using an “integrating sphere” or “goniophotometer”. Unfortunately, professional equipment to measure lumens can be very expensive, but there are inexpensive solutions. To make this measurement, you (1) Fig.33: an inexpensive light meter that you can use to measure lumens. This Neewer meter shown can measure up to 200,000 lux. You can find a variety of these types of meters online, mostly sold at quite reasonable prices. 24 Silicon Chip Australia's electronics magazine Fig.34: a DIY lumen measurement with a hollow foam sphere, as described by run4jc. need a way to collect all the light coming from the torch, (2) a way to measure the illuminance and (3) a reference for calibration, such as a torch with a known accurate lumen rating from a reputable manufacturer. The illuminance can be measured using an inexpensive light meter; searching eBay for “lux meter” brings up many models under $50 (see Fig.33). The light collection device is ideally a sphere, but it can be a white foam box, a white foam sphere or even PVC plumbing fittings. Even a cardboard box with the inside painted white will work. The torch under test is shone into a hole in one side, and the collected light is measured (in lux) with a light meter inside the device. First, the reference torch is measured, and a conversion factor is calculated between the lux reading and the known number of lumens. This can then be used to measure unknown torches. Ideally, the calibration torch brightness is similar to the unknown device. You can get hollow foam spheres in Australia from Amazon and eBay; try Googling “hollow foam ball”. A method for making an integrating sphere from a hollow foam sphere is described at siliconchip.au/link/abga – see Fig.34. Another hollow sphere method is described at siliconchip. au/link/abgb Brooke Clarke describes the use of a professional integrating sphere for flashlight measurements with an accompanying video at siliconchip. au/link/abgc Also see the video by Matt Smith titled “DIY Lumen Measuring Device. Integrating Sphere and Lumen Tube” at https://youtu.be/xOE18kJ5WAU (refer to Figs.35 & 36). siliconchip.com.au Fig.35: a foam packing box can be used as the “integrating sphere” for lumen measurements. Source: Matt Smith video (https://youtu.be/xOE18kJ5WAU). These approaches will be acceptable for most non-professional purposes, but you can obtain surprisingly accurate results. Note that a large proportion of lumen ratings found on the internet are inflated, sometimes by a factor of 10 or more. See Matt Smith’s video titled “Internet Lumens vs Actual Lumens, and the 100 watt LED test” at https:// youtu.be/XIywzCfvunY Flood, throw and spill beams Torch light beams may be more ‘flood’, more ‘throw’ or a combination (see Figs.37 & 38). Flood beams are better for indoor and local area Fig.36: using PVC plumbing fittings as the “integrating sphere”, often called a “LumenToob”. Source: Matt Smith video. illumination, such as around a campsite. Throw beams are better for illuminating objects at a distance and tend to have a central ‘hotspot’. The spill beam is the light outside the central hotspot that comes directly from the emitter and not via the reflector. Reflectors and lenses Reflectors are important and, along with the nature of the bulb, determine the amount of flood or throw the light has. Some torches have reflectors with a variable focus to control this. Generally, smaller diameter torches have a more flood-like beam because of the smaller, shallower reflector and larger lights have more throw because of the deeper, larger reflector. Reflectors may be smooth or have an “orange peel” texture. Orange peel reflectors give a smoother beam; smooth ones give a better throw but have more visible beam artefacts. Lenses may be plastic or glass; better ones have an anti-reflection (AR) coating. TIR lenses are a special type of torch lens; TIR stands for “total internal reflection”. These are alternatives to reflector style lenses and are said to produce a better quality, fully collimated beam, unlike reflector optics. In a TIR lens, all light goes through the What is your EDC? EDC stands for “everyday carry” and refers to the torch you usually carry with you. It might be on a neck lanyard, a keyring, in a pouch or a pocket, and there might be more than one. EDC can also refer to other tools one might carry, such as a multi-tool, pocket knife, notebook, pen, watch, lighter, phone, charger pack etc. Fig.37: flood vs throw beams and a combination of both, directed by the reflector. Not shown here is the ‘spill beam’, light that comes directly from the light source and does not go via the reflector. Flood vs throw can be varied using a ‘zoom’ or variable focus feature. Fig.38: examples of a flood beam (left) and throw beam (right). Source: www.candlepowerforums.com/threads/spill-vs-flood.252751/ siliconchip.com.au Australia's electronics magazine An EDC organiser pouch, filled with various EDC items, including an Olight torch. Source: https:// everydaycarry.com/posts/35528/ trending-maxpedition-micropocket-organizer November 2022  25 lens, but in a reflector, not all light exits via the reflecting surface (see Fig.39). Guide to choosing a torch Fig.42: the components I purchased to build a Convoy S2+ torch. The parts that came as the ‘torch host’ are at the top, while the ‘pill’ is on the left side of the middle row. The optional lenses and lighted switch components are in the bottom row. When purchasing a torch, there are many factors to consider, including: ▢ Spend as little or as much as you want but remember that some inexpensive torches can be surprisingly good. Read reviews and watch review videos. An inexpensive torch we like is the Convoy S2+, described opposite. ▢ Try to ensure you are getting a genuine product, not a fake one. ▢ What size torch is required? ▢ What is the required lumen output and number of brightness settings? ▢ How much ‘flood’ or ‘throw’ beam or combination thereof do you need? ▢ If it has a rechargeable battery, is recharging convenient in your intended application or might disposable batteries be better? Some torches have a built-in USB charging port, so no dedicated charger is necessary. ▢ Do you want to use standard cells that can be purchased anywhere, such as AA, AAA or D, or a less common specialist type like the 18650? ▢ Does it have a long enough runtime at various power levels for its intended application, plus extra time for emergencies? My Convoy S2+ with an SST40 LED and eight AMC7135 drivers lasts around a week on the lowest brightness setting with a Sony VTC6 3000mA 18650 cell, perhaps longer. ▢ Some torches have a small parasitic battery drain, meaning the battery might be flat when you go to use it. Check for that. The tail cap can often be unscrewed to break the circuit for storage. ▢ Is the battery removable? If not, it could be a problem if it fails or you want to upgrade it. ▢ Does the torch use special custom batteries? For example, Olight uses product-specific batteries in some models. ▢ Is it multi-voltage; eg, can it use either alkaline or lithium batteries? ▢ Do you need a splash-resistant or waterproof torch? ▢ Is it shaped so it won’t roll away on an incline? ▢ Are there points to attach a lanyard? ▢ Does it have a crenulated bezel (Fig.40)? If the torch is set to a low setting and placed face-down on a flat Australia's electronics magazine siliconchip.com.au Fig.39: the difference between conventional reflector optics (left) and a TIR lens (right). Source: LEDiL Fig.40: a Nitecore SRT7 with a three-prong stainless steel crenulated bezel, an optional accessory on this discontinued model. 26 Silicon Chip Fig.41: a Lumintop FWAA torch with a two-way pocket clip that can be attached to the brim of a hat, into a pocket or onto a belt. surface, this allows a small amount of light to leak out, to provide a low level of illumination. In some cases, the bezel can even be used as a glass-­ breaking tool to rescue someone from a car or building. ▢ Can it tail stand? This can be useful to provide “ceiling bounce” light. ▢ What is the switch type, where is it and is it replaceable? Tail cap switches can be ‘forward’ (the torch will momentarily switched on if the switch is depressed halfway) or ‘reverse’ (momentarily switched off with a half-depression). ▢ Does it have a pocket clip, and is it one-way or two-way (Fig.41)? ▢ Does it have a magnet to attach to magnetic metal? ▢ Does it have a glow-in-the-dark (GITD) switch or o-ring? If not, GITD replacement O-rings can be purchased. ▢ How complicated is the user interface? Can you remember all its functions, or should you keep instructions with you? ▢ Can it be completely disassembled to modify or repair? ▢ Is there an active “modding” community? Is the torch easily modifiable? ▢ Are spare or other parts available? ▢ Check user reviews SC Building your own torch I purchased the parts shown in Fig.42 to build my own version of a Convoy S2+ from the “Convoy flashlight Store” on AliExpress (https://convoy.aliexpress. com). These parts can be purchased at many places, but they seem reliable. The parts are: Host body: Convoy S2+, which includes an orange peel reflector, pill, o-rings, glass, battery spring and lanyard for under $15 Driver: 7135 × 8, 17mm 3040mA 12-mode group driver with built-in temperature control, compatible with lighted switch, for under $9 LED: Cree XML2T6 3B LED for just over $5 Lenses: a range of TIR lenses with different illumination angles, compatible with XML and XML2 LEDs for about $4 (optional) Lighted switch: $4.95 (optional) Postage was a few dollars. Parts and tools I already had include an 18650 Li-ion cell and charger, thermal paste, solder and a soldering iron. The Cree XM-L2 T6 3B emitter came on an MCPCB (metal core printed circuit board) base. It handles up to a 3A and 10W and gives 1052lm output. T6 refers to which luminous flux group it is sorted into (280-300lm <at> 700mA), and 3B refers to its tint and colour temperature, 6200K cool white. Fig.43 shows how it is assembled into the pill and its relationship to the driver. Note solder pads for the emitter and other pads for + and – wires from the driver. Glossary of Terms Beamshot a picture of a torch beam, typically on a wall or in a natural environment and often used for comparisons between lights. Colour rendering index the ability of a light source to accurately render the colours of objects it is illuminating (also called CRI). A CRI of 100 is identical to daylight; lower numbers give worse colour rendition. Donut hole an undesirable dark spot in the centre of a torch beam. EDC everyday carry (see panel). GITD glow in the dark. HA hard anodised; a surface treatment applied to aluminium. Hotspot the centre part of the beam; a brighter hotspot provides better throw. Low voltage shutdown the torch shuts down if the battery voltage gets too low. Lithium-ion batteries can be ruined if their voltage goes too low; some such cells have their own low-voltage shutdown. Memory when the driver remembers the last mode it was in, eg, if you turned the light off at medium brightness, it would turn on again in that mode. Pill the part of the torch which is a mounting point and heatsink for the LED on one side and the driver on the other – see Fig.43. Fig.43: assembling the Convoy S2+ is pretty straightforward; this shows how the ‘pill’ goes together. The LED is on one side and the driver is on the other, held into the pill by a retaining ring. The driver wires must be trimmed and soldered to the LED PCB, and thermal paste should be added between the LED PCB and the pill. siliconchip.com.au Protected cell a cell with a small PCB to protect against over-charge, over-discharge and possibly over-current. Not all torches can accept protected lithium cells as they are several millimetres longer than standard cells. Unprotected cells can be safely used in torches with low voltage shutdown. Tactical flashlight military-style, but it essentially is a meaningless marketing term (some may disagree!). Thermal shutdown the torch will shut down if it gets too hot. The driver usually provides this function. UI user interface. Australia's electronics magazine November 2022  27