amber-drift

The phenomenon whereby an incandescent lamp becomes more amber (or yellower) as it is dimmed. The exact formula for color temperature dependent on voltage is: coltemp/COLTEMP = (volts/VOLTS)^0.42. Thus a 3200K lamp at 50% voltage (not necessarily 50% on the control console due to the square-law dimming curve), will have a color temperature of ~2400K.

The effect can be counteracted somewhat by the use of CTB, 1/2-CTB, 1/4-CTB, and 1/8-CTB color filters.