Interesting comparison djozz. Sorry for replying so late. Im more interested in the practical stuff, but I appreciate the effort on the theoretical part as well. :beer:
Ill share some thoughts/questions regarding the typical cheap budget meters (may not be wise to assume they are all fairly similar). What you think about them?
-Trying to find out if certain emitters are the bin they state are hard. Example. XM-L2 U2 1A vs XM-L2 U2 2C If you compare several of each emitter, and find out that 2C does read a bit lower, it does not necessarily have to not be U2 bin. It may just be the (cheap) lux meter showing lower number due to the wavelength.
-When comparing domed and de-domed emitters, the loss may not be as large as measured by typical cheap lux meters. As an example, my latest de-dome job (3x XM-L2) showed 10% loss, but it may have been less if measured with a better lux meter. (Im mostly using my LX-1010B, which I assume is quite similar or the same sensor as your LX-1010B)
-Your measurements on de-domed XP-L showed basically zero loss right? Could this be due to having less of a "strange change" in tint compared to XM-L2? Im not much familiar with de-doming those emitters yet, so feel free to fill me in. Just wondering if some of the before/after changes that we expect when de-doming are more exaggerated due to cheap lux meters.
-Difference when measuring the color emitters were quite disturbing.
-Getting people`s calibration closer to each other others are IMO easily doable if people (who buys a lot of lights) are willing to put in a little bit of effort and calibrate their numbers a bit closer to various other peoples calibrations.
Sending out "calibration lights" would require several lights with different beams and tints in order to better get some accuracy. For some it may not be relevant to use 4C as a calibration reference, since some people mostly stick to emitters in the 4800-7000K range. On top of that, if there is only a single light, and that light is measured with a lux meter with an "old calibration" that may or many not be that accurate, what would be the purpose then? We know different meters are likely to have different readings with different tints. And we are not sure that a meter that was calibrated a long time ago me be perfectly accurate today. Basically, the calibration may not become more accurate, and you would have to get "everybody" in on the same calibration. And that is the main issue, and not very likely to happen. Also, IMO if some project with sending out calibration lights at some point did happen, they would also have to be reference lights for lumen in order to be worth the effort and to attract more people.