Originally Posted by Citation4444
You have to be very leery of believing the lux numbers these cheap meters read when measuring projectors. They are designed and calibrated for environmental light measurements, not spectra like we get with projectors. I think these meters are ok for measuring the dimming of your pj lamps as long as the same meter is used each time.
Here is a little experiment I ran today to show how much different these meters can read when measuring different spectra.
I have 3 meters that will measure lux directly: a Konica-Minolta CL-200 (a $3000 meter that presumably is the most accurate), an AEMC CA813, and an LX1330B. The latter two are popular here on the forum, the CA813 for a long time and the LX1330B is the one Ron Jones recommended a few posts ago. The LX1330B is the newest as I just bought it today.
First, measuring projectors. I used a 100% white window from my Lumagen XE, using the smallest window it produces. This allows me to precisely position each meter's sensor. I have 2 projectors: a Sim2 MICO 50 and a Sim2 C3X720. The spectra of these two are quite different with the MICO using RGB LED's as the light source and the C3X using a UHP lamp. Here is what I measured:MICO 50
Konica Minolta CL-200
113 lx equating to 509 lumens for my screen
103 lx (-9% from CL-200), 464 lumens
128 lx (+13% from CL-200), 576 lumensC3X720
Konica Minolta CL-200
213 lx equating to 960 lumens for my screen
176 lx (9% lower than CL-200), 792 lumens
224 lx (13% higher than CL-200), 1008 lumens
Thus, for my MICO 50 I can get readings from 464 to 576 lumens depending on which meter is used.
And, for the C3X720 I can get readings from 792 to 1008 lumens.
Which one is right? I believe the closest is the Konica-Minolta CL-200 which correlates with off the screen measurements using my i1 Pro. However, calculating lumens from the i1Pro requires me to know my screen gain, which I think I know pretty close.
As a further check, I used all three meters to measure the lumen output from one of the incandescent spots in my home theater. In this case, the KM CL-200 and the LX1330B were very close, with the CL-200 measuring 201 lx and the LX1330B measuring 196 lx, within 2% or so of each other. This incandescent light is probably closer to what the meters were calibrated to. The CA813 measured quite low at 167 lx, down 17% from the CL-200.
The only point I'm trying to make here is to not fixate on the absolute lux measurement from these cheap meters as they are probably wrong. Comparing what your projector puts out to someone else's using different meters is probably not a good idea. Using these cheap meters to measure trends, or how your lamp is ageing, is a much better idea.
Addendum: In the manual for the LX1330B it says: "Calibrated to standard incandescent lamp at color temperature 2856K". The Konica-Minolta CL-200 is calibrated with two user-selectable modes: one with a UHP lamp from a projector and the other using an 800lux standard illuminate A. I always use the mode that's calibrated with the UHP lamp. This further supports my opinion that the CL-200 is the more accurate of these meters.