Color Temperature Match Helper

Why mired math beats raw Kelvin for planning

Color temperature in Kelvin is familiar, but Kelvin steps are not perceptually uniform. Moving a lamp from 2800K to 3000K looks like a bigger change than moving 5800K to 6000K. The mired scale fixes that by using one million divided by Kelvin. Equal mired steps look more even, which is why gels are rated in mired shift. This helper calculates blends and corrections in mireds and converts back to a target camera white balance so the numbers map cleanly to what you see on a monitor.

Three ways to choose your white balance target

Weighted blend works for most real rooms. Give the key a weight of one point zero, fill around half to three quarters, and smaller values for hair, accents, or background practicals. The tool averages the sources in mired space so the target splits the difference in a way that minimizes total correction. Dominant source suits scenes where one practical defines the look. If tungsten bulbs are in frame, pick that as the anchor and cool daylight to meet it. Custom white balance is there when you have a meter reading from a grey card or you want a deliberate lean warmer or cooler. Enter the Kelvin and the rest of the plan adapts around your choice.

What gels actually do in practice

CTB cools by subtracting mireds; CTO warms by adding mireds. Typical values are about minus one hundred thirty for full CTB and plus one hundred thirty for full CTO, with halves, quarters, and eighths forming smaller moves. The calculator selects one or two elements to approximate the exact shift for each source and then reports the expected resulting Kelvin. Residual error shows how far a corrected source still sits from the target. On camera, a small residual rarely matters, especially if you have consistent skin tones and balanced highlights.

Temperature first, tint second

The plan focuses on temperature only. Real fixtures vary in green or magenta. Many office LEDs tagged four thousand Kelvin push green; some budget panels turn magenta at low dim levels. After you match temperature with CTO or CTB, check a grey card or neutral patch on a vectorscope. A drift toward green calls for a little plus green. A drift toward magenta needs a minus green. Add a small piece, recheck, and note the fix in the export text so the team can repeat it the next day or on a second unit.

Simple weights that save time

Weights do not need a meter if you lack one. Use the scene logic. The closest and brightest source gets one point zero. A bounced fill might get zero point six. A small lamp in the back might get zero point two. If diffusion changes transmission, update the weights. If you flag a window or close a blind, update the weights. When anything that hits the subject changes, recompute and copy the fresh plan so there is no hidden mismatch between intent and setup.

Fast plays you can trust under pressure

If daylight dominates, white balance around five thousand two hundred to five thousand six hundred Kelvin and bring warm lamps up with CTB fractions. If tungsten dominates, white balance near three thousand two hundred Kelvin and warm daylight with CTO fractions or reduce the spill. In mixed offices, a neutral custom target near four thousand five hundred Kelvin reduces fighting. Correct the one or two worst offenders and leave the rest if time is short. The goal is pleasing skin and stable continuity across angles, not absolute lab precision.

Workflow that stays friendly on mobile

The interface keeps text in straight lines so you can read and act quickly on a phone. Tiles summarize the target white balance, the dominant source, the average mired move, and the largest residual. The table collapses into tidy cards with labels on the left and values lined up on the right, matching your other tools. Nothing uploads; all math runs in your browser. Use the copy block for shot notes, export JSON for automation, or CSV for a quick spreadsheet. A screenshot of the table beside a lighting diagram is often enough for a small crew to rig without extra messages.

Limits to keep in mind

The plan assumes one color channel per source and does not model spectral quirks or color rendering index. It ignores camera specific metamerism and any look transforms. It also does not manage hue shifts from dimming tungsten or LED spectrum shifts at low power. Treat the numbers as a fast map. Confirm with a card and adjust a single gel size if needed. Consistent notes and a repeatable flow will save more time than chasing exact matches that drift with every subject and costume.

What line format should I use?

Use Kelvin followed by optional weight and a note. Example: 5600K @1.0 key. Weight defaults to 1.0 when omitted.

When is dominant source the right choice?

Pick it when a single practical defines the scene and must win, such as tungsten bulbs in frame or a hero fixture you cannot change.

How accurate are gel stacks here?

Stacks use typical mired values for CTO and CTB. They are close enough for planning. Final tweaks should follow a quick grey card check.

Does this handle green or magenta tint?

No. After temperature is matched, add plus or minus green based on your scope or a calibrated chart.