I've been tending to use my i1Pro Rev E (i.e. i1Pro2) for random spot measurements a lot. Recently it's accuracy had been niggling at me. What I noticed was this: From cold, do a calibrate. Measure spots. The errors would rise (literally the L* was rising). The closer the measurements together, the faster the errors would rise. Let it cool, and the errors would drop. Recalibrate hot, and the error would increase as it cooled down. At its worst, I as seeing errors of 2.0 Delta E between cold and hot! [ It's pretty easy to replicate this experiment - ArgyllCMS spotread makes it straightforward, but you could do something similar with ColorPort etc., repeatedly measuring the white calibration tile. I noticed this type of thing before with one of the i1pro Rev A's I've got, but it wasn't as extreme, and I put it down to being an old lamp in a well used instrument. ] Then it got weirder. This characteristic didn't seem stable. I started looking at how it was affecting strip measurements, and it kept changing. Sometimes it would get better. Then it would get worse again. Then the light went on (so to speak), and I arrived at a theory. What if the lamp is a miniature Quartz Halogen lamp ? This would make sense in terms of how long the lamp should last, QH lamps typically last 2-5 times longer than conventional incandescent lamps, and would also be helpful in ensuring constant light output over the lamp life, something that is rather desirable for an instrument light source. I measured a color temperature of just over 3000K, which is consistent with a hotter QH lamp. <https://en.wikipedia.org/wiki/Halogen_lamp> QH lamps work on the basis of re-circulating evaporated tungsten back onto the filament. To do that they have to get hot enough to evaporate any that gets deposited on the inside of the glass, and even hotter to disassociate the resulting halide back into tungsten at the filament. If the spot measurement gets the bulb hot enough to evaporate tungsten from the filament and the glass, but not quite hot enough to deposit it back at the same rate onto the filament, then the glass will build up a layer of tungsten on it. This reduces light output. As it warms up a bit, the tungsten gets evaporated from the glass, increasing light output. When it gets cold again the tungsten gets deposited back on the glass. Hence my increasing L* error as the instrument warms up, and hot/cold behavior. But if the bulb gets warmer still, say by being used for strip readings, then the tungsten gets re-deposited on the filament, and the bulb gets "cleaned". So after some extended strip readings (i.e. several measurements in a row, made with the button down and the lamp on for as long as possible), the instrument no longer displays such dramatic error increases with temperature. In fact after "cleaning", the worst I could get was 0.08 Delta E, a 20x reduction, and back in line with instrument specifications. If you predominantly use your i1Pro for reading strips, you probably haven't noticed this effect at all, because your lamp isn't getting dirty. I've seen similar effects on all my i1Pro's, and also Spectrolino's, although none as dramatic as the Rev E was. So if you do lots of spot measurements with your i1Pro's, and get the impression that your accuracy and consistency of measurement is getting squirrelly, you may be right. But there is a way of fixing it! [ Also posted to Luminous Landscape Forum. ] Graeme Gill.