Introduction
The Color Temperature Mixer calculates the blended color temperature when two light sources of different Kelvin values illuminate the same subject with different intensities. Enter the Kelvin value and lux (or relative intensity) of each source, and the tool returns the mixed color temperature in Kelvin, the mired shift between the two sources, and the CTO or CTB gel required to bring the weaker source into balance with the dominant source. Use it when combining practicals with a key light, mixing daylight with tungsten fill, or correcting a mixed-light interview setup.
What This Tool Calculates
Color temperature mixing uses the mired (micro reciprocal degree) scale for linear interpolation, since the Kelvin scale is non-linear. Mired = 1,000,000 / Kelvin. Mixed mired = (Mired1 × Lux1 + Mired2 × Lux2) / (Lux1 + Lux2). Mixed Kelvin = 1,000,000 / Mixed Mired. Mired shift for correction = Mired_source − Mired_target. Worked example: 5600K key (Lux = 1000) + 3200K fill (Lux = 500). Mired1 = 178.6, Mired2 = 312.5. Mixed Mired = (178.6 × 1000 + 312.5 × 500) / 1500 = (178,600 + 156,250) / 1500 = 223.2. Mixed Kelvin = 1,000,000 / 223.2 = 4,480K — a slightly warm daylight balance.
The Formula and How It Works
An interview setup combined a 5600K LED key (1,200 lux) with tungsten practical wall sconces at 3200K (200 lux combined). Mixed result: 5,128K — close enough to 5600K that a camera WB of 5100K balanced both without visible color cast. For a period drama practical-motivated interior, a 3200K Joker 400 key combined with 6500K window daylight fill at 30% of key intensity gave a mixed result of 3,880K — requiring a Half CTO on the daylight source (shifting from 6500K to approximately 4,000K) and a WB of 3,900K for the cleanest grade. A product commercial mixed a 4000K LED ring light (dominant) with a 5600K LED backlight at 40% intensity: result was 4,540K, corrected to 4000K by placing 1/4 CTB on the backlight.
Real-World Examples
Mired Values for Common Color Temperatures
2700K (incandescent bulb): 370 mired. 3200K (tungsten film): 312 mired. 4000K (warm white LED): 250 mired. 4500K (midday shade): 222 mired. 5600K (daylight/HMI): 179 mired. 6500K (overcast sky): 154 mired. 8000K (heavy overcast): 125 mired. Mired shift required for Full CTO (3200K to 5600K): 312 − 179 = 133 mired. Half CTO provides approximately 65 mired shift. Quarter CTO provides approximately 33 mired shift.
Pro Tips and Common Mistakes
| Detail | Value |
|---|---|
| Mix color temperatures in mired, not Kelvin. | |
| A 1000K difference at 3000K (333 vs 312 mired = 21 mired) looks very different to the eye than a 1000K difference at 6000K (167 vs 154 mired = 13 mired), even though both are the same Kelvin gap. | |
| The eye is most sensitive to color temperature differences in the 3000–5600K range. | |
| The most common mistake is assuming that equal lux from two sources means equal visual weight in the mixed result. | |
| The warmer source (higher mired value) dominates the perceived color cast even when it contributes less lux, because warmer light contains more energy in the red channel that the camera sensor responds to more strongly in low-light conditions.. |
Pro Tips and Common Mistakes
Pro Tips
- Mixed-light correction is one of the most time-consuming problems in location lighting.
- The standard advice — match everything to one color temperature — ignores the reality of practical-motivated setups, location windows, and available light augmentation.
- This tool gives you the exact gel correction needed in under 10 seconds..
Common Mistakes
Frequently Asked Questions
What is a mired and why is it used for color temperature mixing?
Mired stands for micro reciprocal degree: 1,000,000 / Kelvin. The mired scale is linear for human color perception, meaning equal mired shifts look like equal color changes to the eye regardless of the Kelvin value. The Kelvin scale is not linear, so mixing Kelvin values directly produces incorrect results.
How do I set white balance when mixing two color temperatures?
Set the camera white balance to the mixed color temperature the tool calculates. If you are shooting RAW, you can correct in post — but setting an accurate in-camera WB gives the colorist an accurate starting point and reduces the risk of clipping in one color channel.
Can I mix more than two light sources?
Yes, using weighted mired averaging. Add a third source: Mixed Mired = (M1 × L1 + M2 × L2 + M3 × L3) / (L1 + L2 + L3). Run two sources through the calculator first, note the mixed result and combined lux, then treat that as one source and mix it with the third.
What is the color temperature of a practical light bulb?
Incandescent and halogen bulbs run at 2700–3200K. Compact fluorescent bulbs labeled warm white are typically 2700–3000K; cool white or daylight bulbs run 4000–6500K. LED retrofit bulbs vary widely — always check the Kelvin label on the packaging, as LED color temperature depends entirely on the phosphor blend used.
Start Calculating
Use the calculator above to run your numbers before your next production.
