Correct, Gretag Macbeth is the only place you can get your MacBeth light calibrated. And, yes, it needs calibration.
Simulating different light sources requires that the lamps and unit are putting out the correct heat, visible spectrum, current, etc...
These values must be accurate in order to simulate the various light sources. A bulb, for example, that should be operating at say 200K, will not have the correct output if it is only running at 180K.
It is expensive also, about 500 USD per unit + parts and they send an engineer onsite to do the calibration. We run 10 booths and they must all be calibrated on a yearly basis.
