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LS172 Colorimeter review Linshang LS172 Colorimeter If you want to find a paint colour that matches your existing paint or verify that batches of products you are ordering have matching colours, this device is perfect. It’s relatively inexpensive, very accurate and quite easy to use. It even costs less than a single colour sensor we recently looked at! Review by Allan Linton-Smith T he LS172 is a hand-held colorimeter that’s ready to use out of the box. It is capable of accurate measurements and allows you to easily compare the colours of different objects. It uses reflected light from a LED beamed onto a sample, analysing colour and intensity. It is an essential tool for anyone involved with colour measurement, such as painters, decorators, or anyone requiring standardisation of coloured items. It gives you CIELAB (L*a*b*) measurements (when translated from French to English, CIE stands for the International Commission on Illumination) and can also measure tiny colour differences. Additionally, it can convert colour values into Pantone numbers, which printers and colour consultants often refer to. It costs around $250-300 depend- ing on where you buy it; it is available from eBay, Amazon, AliExpress and other online retailers. That might sound expensive, but it’s cheap compared to what was available before! For comparison, the Omron BW5C colour sensor can be purchased from DigiKey for around $280. And that’s just for the sensor! The LS172 is undoubtedly good at matching house paint; I recently used it to match my house colour to a colour sample at the hardware store. I used its memory to store my house colour CIELAB measurements. I then checked out similar colour sample cards until it gave a “green” reading, indicating that the sample was almost identical to the house colour. The colour it identified was “Beige Royal”, which it indicates is similar to Pantone 7527 C or Pantone 7434 C. It LS172 Features & Specifications » » » » » » » » » » » » 54 Background image: https://unsplash.com/photos/46juD4zY1XA Illumination: full-spectrum LED, 45° annular illumination, 0° viewing angle Measuring aperture: 8mm, 10° field of view Measuring time: about one second Colour standards supported: CIELAB, Pantone, Luv, LCh, Yxy, CMYK, RGB, Hex Colour difference formulas: ΔE*ab, ΔE*uv, ΔE*94, ΔE*cmc(2:1 or 1:1), ΔE*00 Standard deviation for ΔE*ab: ≤ 0.03 (average of 30 white tile measurements three seconds after calibration) Dimensions: 86×62.5×158mm, 225g Power supply: rechargeable 3.7V 4000mAh Li-ion cell; 10,000 measurements from full charge Display: 480×320 pixel IPS colour LCD screen Charging port: Type-C USB Operating conditions: 0-45°C, 0-85% relative humidity (no condensation) Language support: English, Simplified Chinese also tells me that Beige Royal is ‘more white, slightly more red and slightly more blue’ than my house colour. The device can store 1000 colour measurements, so you can keep your kitchen, bathrooms and other samples for reference if you want! The hardware store I went to has a colour-matching system but no CIELAB reference or Pantone numbers, meaning I would have to chip off a bit of paint from my house to match it. I much prefer using the LS172 to damaging the house! Note that smartphone photos are not good enough to match colour accurately because of lens filtering and light source variations, which can easily shift the colour and intensity and result in an imperfect match. There’s also no guarantee that a phone camera has a wide enough colour gamut to distinguish all colours the human eye can. The CIELAB colour space The L*a*b* numbers represent any colour and its brightness with three coordinates. The L value indicates the brightness, with 100 being pure white and 0 pure black. The other two values, a & b, represent the colour’s hue and saturation, ranging from -128 to +128. They are the x & y coordinates on a standard colour chart, shown in Fig.1. Note how the centre is unsaturated (grey) and colour saturation increases as you move towards the circle’s circumference. Practical Electronics | October | 2024 LS172 Colorimeter review Therefore, the a & b coordinates encode both the shade (hue) and colour intensity (saturation). Adding L (brightness) gives you everything you need to define a colour. The entire colour space approximates the range of human daylight vision. I measured the yellow lid of a Vegemite jar, which was indicated as L=71.6, a=7.8, b=87.4. Interestingly, using the LS172 to compare the lid to the label, it said they did not match and that the label was “more white, more green and more blue”, even though it looked identical to my eyes! You can find more details on L*a*b* colours at https://w.wiki/7GRT Using it The LS172 is really easy to use. All you need to do is place it on a flat item such as a wall, door or colour card you wish to match. You can then store its colour as the “standard” and compare it to various samples later, to find a match or determine exactly how different they are. A typical screen image during use is shown in Screen 1. It calculates the delta (difference) between your standard and your sample and tells you if you pass or fail with a green or red background to the delta bar. There are various options for calculating the delta estimate; we used the standard “ΔE*ab”. You can also change the delta threshold that determines its sensitivity to differences. As mentioned above, it gives you the delta figures and human­-readable text like “more blue” or “more yellow” etc. This can be handy since, as I wrote, they often look identical to the eye. If you were mixing paint, you could use those hints to add a small amount of extra tint to end up with a spoton mixture. The LS172 calibrates instantly using the little tile in its protective cover and requires no external calibration. It is easily recharged with a USB-C charger and you can just put it in your pocket or handbag (although it’s a bit chunky to carry comfortably in our pockets). Its built-in rechargeable Li-ion battery is claimed to be good for 10,000 measurements with a full charge. It has a user-friendly 3.5-inch (89mm) diagonal touch screen and can quickly match the closest PanPractical Electronics | October | 2024 tone colour number with a claimed accuracy above 90%. One of the excellent practical features is the on-screen retention of the saved colour; the comparison colour is also saved in a split screen for easy reference. b+ How is it? In summary, the LS172 is a cost-­ a− effective tool for those involved in colour specifications, colour analysis and colour control. It is a versatile instrument with an excellent memory and can quickly be set up for various analyses. For more information, visit the manub− facturer’s website at pemag.au/link/abpi Finally, the Editor had a good ques- Fig.1: a ‘slice’ through the L*a*b* tion: what if you want to match a me- colour space at around L = 50, halfway between white and black, tallic finish, like many automotive giving a neutral grey shade in the paints? I guess the answer is that it centre. The example coordinates would require a different type of in- shown here, a = 55 & b = 40, give a strument; after all, no instrument can peachy colour. As this is circular, do everything! √a2 + b2 ≤ 128. Since the magazine A bit of history Early colour measurements and colour matching were done with pretty crude devices such as a “colour comparator”, a circular dial of various colours that you put against a sample. When it matched by eye, you noted the colour number on the dial. However, it rarely matched perfectly! For liquids, we used “standardised nestle” tubes, large test tubes of exact dimensions that we held up to daylight to compare with a sample of a previously standardised product. These methods relied on subjective evaluations and depended on the light source and human judgement. Tungsten light can easily hide colour differences; the LS172 uses pure white light from its LED source. Also, not everyone has perfect colour vision. Where I worked, an Ishihara test was given to laboratory staff before any colour decisions could be made. Approximately one in 12 males and one in 200 females are colour-blind. You can take the test yourself at www.colormax.org/color-blind-test/ The origin of CIELAB Richard Hunter developed colorimeters and the L*a*b* system in the 1950s to quantify exact colour hues and intensities using numerical values determined by reflected light. Hunter’s colorimeters were first used a+ is printed in CMYK, this figure will not be displayed accurately. Source: https://chromachecker.com/manuals/ en/show/chromaspot Screen 1: the main screen during use. You can see the measured L, a, b, C & h values at top middle in blue, with the reference values in black to their left. The differences are shown to the right and summarised in the green bar just below the middle of the screen. The perceptual differences are shown on the right. C is for chroma and h is for hue. 55 LS172 Colorimeter review Left: a Gardener Laboratory L*a*b* Colorimeter and power supply weighing around 20kg (owned by the author) compared to the LS172. The LS172 is smaller and lighter than the laboratory unit’s colour sensor head! Below: here is the LS172 measuring the colour of a pink sheet. The device provides multiple matches of different Pantone colours. The LS172 also includes a “calibration tile” as part of the bottom cap, which is shown inset. This tile is used as a white reference during calibration. commercially by Proctor & Gamble to accurately standardise the colours of their soaps. The giant company Dow then adopted them to measure and standardise plastics. I was fortunate to meet Richard many years ago and was delighted to play around with one of his early colorimeters. Convinced that it would be a game changer in the R&D lab where I worked, I put in a request to get one. I wanted to numerically standardise tomato paste, tomato sauce and various fruit concentrates to ensure consistent quality and help select the best raw materials. However, the response I got was, What is Pantone? “$8,000 for that! Can’t you just use your eyes?” Most serious food labs now have such a colorimeter. The photo above shows my Gardener XL-800 Series display plus XL-825 Optical Remote Sensor Colorimeter. It operates only from 110V AC, consuming over 600W, so it requires a huge 230V to 110V stepdown transformer. It is now obsolete and destined for a museum; a decision I made after testing the little LS172! Richard Hunter told me that he sold many instruments to forensic labs to compare paint fragments for motor vehicle “hit and run” cases; his instruments were so sensitive that they were Pantone is a proprietary colour-matching system developed by the company Pantone LLC. Individual colours are named and matched to a specific printing process (called the Pantone Matching System), with the type and quantity of ink or pigment used cross-referenced to their name. The importance of Pantone colours comes from the accurate reproduction and standardisation. This means that no matter the location, a specific Pantone colour will display and be printed exactly the same (assuming the printer follows the standard). It’s common for logos to be specified using Pantone colour(s), so that no matter if it’s printed on a metallic can, wooden box or piece of paper, it will look the same. 56 able to match paint chips on victims to the exact offending car because no two cars are exactly the same colour! Evidence with L*a*b* measurements is now accepted in most courts. Spectrometers were also used (and still are) to display colour spectra absorbance of liquids vs wavelength in nanometres over the visible range. However, such measurements require expert interpretation, and you need a large data bank of standard colour spectrograms for comparison. Early colorimeters such as the Gardener were very heavy, used a lot of power and were consequently restricted to bench work. They were also difficult to calibrate. Editor’s note: while the spelling “colourimeter” is sometimes used (along with “colourimetry”), it is not common. In Australia, it mainly refers to a different type of instrument that measures chemical concentrations by absorption of specific light wavelengths. Therefore, we are using the spelling ‘colorimeter’, even though it might appear to be inconsistent with the typical UK/Australian spelling of similar words. PE Practical Electronics | October | 2024