Dear XO! The color temperature of daylight changes but we want to calibrated light source to have a constant color temperature. Dichroic color head generally has 3200K lamp in there. With some Cyan and very little Magenta I can make it becomes a 4700K light source and it would stay that way constantly. I used the spyder2 with the HFHC software to measure color temperature and recheck by shooting the light source with a Nikon Coolpix with the color temp set to 4700K and see if the resulting image is gray.
The filtrations setting which is monitor by the 3 sensors and displayed on the unit digital displays are very accurate. I make a note of the readings for this condition and later all I have to dial in the amount of filter that gives the same reading then the light is the same even if the bulb has aged and changed color and intensity.
And then dial in equal amount of filter on all 3 channel would give it neutral density. Monitoring the actual brightness with an accurate spot meter as reference. (Well you must have an instrument that you can trust to be correct) so I would know how bright the light is.
It works very well except that I only have 5 stops range. The unit has 180cc adjustment and that's 6 stop but I waisted some of the filtration to increase the color temperature.
By the way I used it to check out the light meter on my Minolta SRT-101 and after checking it I decided not to use it. Even I supply the camera a constant 1.35v source via a regulated power supply. I can adjust the calibration resistor to make it read higher or lower but if it's correct at EV14 it's wrong at EV9 and vice versa so I decided to use the camera as a meterless camera rather than trying to get expensive battery for it.