CTB Gel

What this is about

CTB runs the opposite way to CTO and is used when a tungsten unit has to work inside a daylight scene: a lamp helping out a shaded actor at midday, a fixture filling a room whose window sets the balance, or a warm source that has to hide inside a cool night look. The direction is more expensive in light. Full blue absorbs a substantially larger share of the output than full orange, so a gaffer often reaches for a bigger unit or reaches for a bicolour LED that simply dials the temperature instead of paying the loss.

A term only helps when everyone on set means the same thing by it — so what follows is how it is used, not a dictionary definition.

What runs differently here

Where this differs from the general case:

• Full CTB costs noticeably more output than full CTO — around one and a half stops against roughly one is the usual planning figure.
• Because of that loss, crews often prefer to gel the daylight down with CTO instead of lifting the lamp up with CTB.
• Bicolour and RGB LED fixtures make short CTB runs unnecessary, though tungsten units still need the gel.

With TillyGen

TillyGen's lighting notes state the target color temperature per setup, so the equipment list shows whether CTB or a bicolour fixture is cheaper.

Change one constraint and the consequences travel through the whole plan: affected shots are flagged, the call sheet is regenerated, and nobody keeps working from yesterday's version.