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Conversion

Color Temperature Mired Converter (Kelvin ↔ Mired)

**Color temperature (K) is the absolute temperature of a black-body radiator that emits light of the same hue.** Kelvin, however, is *not perceptually linear* — going from 2000 K to 3000 K (+1000) is a strong warmth shift, but 9000 K to 10 000 K (also +1000) is barely visible. **Mireds (Micro Reciprocal Degrees) fix this**: M = 10⁶ / T(K), so equal ΔM corresponds to equal perceived warmth steps. That is why photographic colour-correction filters are rated by *mired shift* (e.g. Wratten 80A = −131 mired) rather than by ΔK — the same filter cools *any* source by the same mired amount. This tool converts instantly between kelvin, mireds and decamireds and lists 15 common light-source references (candle, tungsten, CIE D50/D65, overcast, blue sky).

Color temperature (kelvin)

K

Mired (M = 10⁶ / K)

M

Decamired (M ÷ 10)

dM

Common light sources

  • 1850 K · 540.5 M
  • 2680 K · 373.1 M
  • 2865 K · 349 M
  • 3200 K · 312.5 M
  • 3400 K · 294.1 M
  • 3000 K · 333.3 M
  • 4100 K · 243.9 M
  • 4100 K · 243.9 M
  • 3200 K · 312.5 M
  • 5500 K · 181.8 M
  • 5003 K · 199.9 M
  • 6504 K · 153.8 M
  • 6500 K · 153.8 M
  • 7500 K · 133.3 M
  • 10000 K · 100 M
Formula: M = 10⁶ / T (K). The point of mireds is that equal ΔM corresponds to equal perceptual warmth shifts: a Wratten 80A filter is rated at −131 mired (and it cools any source by the same Mired delta), but the same effect cannot be specified as a fixed ΔK. Decamireds (Mired ÷ 10) are used on Hasselblad-style colour-correction filter wheels.

Formula

Mired ↔ Kelvin: M = 10⁶ / T(K) T = 10⁶ / M Decamired (Hasselblad / German filter scales): dM = M / 10 Filter mired shift (additive): M_filter = M_target − M_source Example: 3200 K → 5500 K requires ΔM = 10⁶/5500 − 10⁶/3200 = −131 mired (Wratten 80A).

Frequently asked

Why are mireds — an inverse unit — still standard in photography? Wouldn't kelvin be more intuitive?

**The answer is visual linearity plus additivity.** **The problem**: black-body radiation peaks at λ_max ∝ 1/T (Wien's displacement law λ_max·T = b), and the human eye does *not* perceive equal ΔK as equal hue shifts — 2000 K → 3000 K is a dramatic shift (deep red-orange to amber), but 9000 K → 10 000 K is barely visible (both cold blue). **Mireds fix this**: M = 10⁶/T linearises the perception, so equal ΔM corresponds to equal perceived warmth shifts. **In practice**: (a) a photographer sees 3200 K tungsten in the room but the camera is set to 5500 K daylight → needed shift ΔM = 10⁶/5500 − 10⁶/3200 = 182 − 313 = −131 mired → pick a Wratten 80A; (b) the same 80A applied to 2500 K (a warmer lamp) and 5000 K (near daylight) targets gives the same ΔM = −131, but very different ΔK (−1500 K vs −2500 K). **The filter spec is portable in mireds**, not in kelvins.

What are decamireds, and how do they differ from mireds?

**Decamired = Mired ÷ 10** (sometimes written dM or 10⁻⁵ K⁻¹). **Origin**: Hasselblad and some German filter brands (Heliopan, B+W) sell colour-conversion filters in ±2.5, ±5, ±10, ±20 decamired steps. **Examples**: (a) **CTO 1/4** (cinema, 1/4 strength tungsten conversion) ≈ −37.5 mired ≈ −3.75 dM; (b) **full CTB** (full blue) ≈ −137 mired ≈ −13.7 dM. **Why**: scale convenience — two-digit decamireds are easier to remember and add than three-digit mireds. **Today**: Kodak Wratten and Lee Filters still use mireds; decamireds appear mostly in European literature and on legacy filter wheels. The tool shows all three so it lines up with any source.

My smart bulb shows kelvin — when do I actually need mireds?

**For everyday smart-LED use, kelvin alone is enough** — apps like Philips Hue or Yeelight show 2700 K (warm) or 4000 K (neutral) and that's all you need. **You need mireds when**: (1) **photography / cinema lighting** — multiple lamps of different colour temperature need balanced *proportions*, computed in mireds; (2) **buying colour-conversion filters** — Wratten / Lee / Tiffen filters are spec'd in mireds; (3) **display calibration** — D50 print white = 5003 K = 200 M; D65 display white = 6504 K = 154 M; the difference ΔM = 46 drives the chromatic-adaptation matrix in an ICC profile; (4) **CCT meters** — Sekonic and Minolta CL spectrometers expose a mired mode; (5) **mixed-light averaging** — a 50/50 mix of 3200 K tungsten and 5500 K window light averages correctly in *mired space* (M_avg = (M_1 + M_2)/2 ≠ T_avg). Verify: K-space average of 3200 and 5500 = 4350 K; mired-space average = (313 + 182)/2 = 247.5 M → 4040 K. Off by ~300 K — that's the kelvin-arithmetic mistake mireds prevent.

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