Lighting · Color temperature
Set WB to your light. Mixed sources? Gel one to match the other, then set WB to that.
A teaching model. Light colors follow the Planckian (black-body) curve; the camera applies per-channel gains so the WB Kelvin renders neutral. Gels use mired shifts: full CTB −131, full CTO +159 (Rosco/Lee nominal), costing about 1.5 and 0.9 stops. The card counts as neutral within about 25 mired (a quarter gel) of the WB. Real dimmed tungsten also warms up; here color stays fixed.