Hello: "2013/5/26 Ben Goren <ben@trumpetpower.com> Not only are they extremely stable, they're extremely consistent between units (no more than 1/10 stop variation, and that may well be due to light placement / aiming). They're also very linear; if I set up the lights in a copy stand configuration and adjust them all by 1/10 stop, the resulting exposure changes by 1/10 stop." But if you measure your working area with your photometer/flash meter with 1/10 stop accuracy and test with Imatest you will note that isn't enought accuracy. There is a different scale for precision from film to digital. On the other hand, UV radiation is cumulative for human tissues, emulsions, pigments, etc. And you can evaluate your light sources graphically through SPD and test CRI (and CQS) with SpectraShop. And if you want, you can make use of those measurements in combination with inCamera (Photoshop plug-in) and ColorChecker SG for profiling. UV cut filter in i1Pro and i1Pro2, no comments. Salud Jose Bueno