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Which gel closes the gap?

To bring a 5600 K window down to 3200 K tungsten you need about 134 mired of warming. Half CTO (LEE 205) and an eighth CTO (LEE 223) add 135 together, one mired over. Full CTO on its own (LEE 204) is 159 and leaves the window about 25 mired too warm.

Updated October 2026 · Gel values are LEE Filters' published mired shifts, the same table the app uses

Gel and mired calculator

An apartment set: a camera operator at a sunlit window, an LED panel on a stand beside him, the talent on the balcony outside
Demonstration frame

ON THE LAMP

Nothing yet. Drag a leaf onto the panel, or tap one in the book.

    SET REF
    SET NOW

    LINK TO THIS GAP

    cutveymeter.com/tools/gel?ref=3200&now=5600

    LEE NUMBERS, AS THE APP NAMES THEM

    PLUSGREEN · MINUSGREEN

    The app treats green and magenta as a rough hint only, so this page leaves them out.

    READING THE CARD

    Δ is how far the light you are measuring (NOW) is from the one you pinned (REF), in kelvin and in mired.

    ADD TO THIS LIGHT names the gels from the LEE book that close most of the gap, never more than two sheets from one series.

    MATCH shows when the two lights are within 5 mired of each other.

    Put a sheet on the lamp and the card works out what is left.

    THE WORKING, IN MIRED
    REF1,000,000 ÷ 3200 K312.5
    NOW1,000,000 ÷ 5600 K178.6
    GAPREF − NOW+133.9
    ADD1/2 CTO, 1/8 CTO+135.0
    LEFTafter those sheets−1.1

    Here it works on the numbers you type. On your phone it reads the light itself. $19.99, once. No subscription.

    Download on the App Store

    The gaps you meet every week

    LEE VALUES · IN MIRED

    Common gaps between two lights and the LEE gels that close them
    FromToGapGel (LEE)Left overLoad
    5600 K window3200 K tungsten134 mired of warming1/2 CTO + 1/8 CTO (205 + 223)−1 miredLOAD
    3200 K tungsten5600 K daylight134 mired of coolingFull CTB (201)+3 miredLOAD
    4300 K LED5600 K daylight54 mired of cooling1/4 CTB + 1/8 CTB (203 + 218)−1 miredLOAD
    2700 K household bulb3200 K tungsten58 mired of cooling1/4 CTB + 1/8 CTB (203 + 218)−5 miredLOAD
    6500 K overcast window5600 K lamps25 mired of warming1/8 CTO (223)−1 miredLOAD

    Worked out with LEE's published numbers, as the app does. Rosco's equivalents differ by a few mired, so from a Rosco book read the answer as a strength, like half CTO.

    Why gels are sold in mired

    Mired is a million divided by the kelvin. A gel shifts light by the same number of mired wherever it starts, which is why the same half CTO works on a 5600 K window and on a 4300 K LED.

    A mired ruler. Half CTO moves a 5600 K window to 3480 K and a 4300 K LED to 2930 K: the same 109 mired, though one is 2120 K and the other 1370 K.