Hi laserlight,
This company specializes in precision optics and precision measurement. They make measurement and calibration devices including light boxes. http://www.maxlevy.com I would guess they can help you.
http://www.netgages.com
I routinely work with calibration labs that calibrate steel gages and masters. The rule of thumb they generally use is to allow masters to "temperature soak" 24 hours in the gage lab before calibration. Keep in mind that masters are generally fairly massive for dimensional stability.
Since...