Which light meter for projector

One of the problems with the accuracy of lux meters in general is they are generally designed for providing the highest accuracy at or near the color temperature of incandescent light. If the look at the spec. for the CA813 (link below) its rated at +/- 5% (some other places it says +/- 3%) at 2856K but for other color temperatures the spec'ed accuracy is only +/- 11% (for what AMEC calls common light sources). Also the AMEC spec. sheet, which covers both the CA811 and CA813, notes that the CA813 "has a better spectral response to common light sources, Model CA811 is used to measure incandescent light sources" (so don't use the CA811 for measuring the light output of projectors). The challenge is for a 6500K light source where the accuracy of the meter's silicon photodiode at the tails of its response curve become very important while for lower color temperatures, not so much so. Even those meters with calibration against a NIST certified source does not assure high accuracy for a 6500K source unless it is specifically calibrated ensure high accuracy for the tails of the response curve, especially for the shorter wavelengths. All this is to say you cannot directly compared the specific results for a projector lumens obtained with one meter against the results obtained with a different meter as they can easily be 5%, 10% or even 20% different.


http://www.aemc.com/products/pdf/2121.21.pdf