Color Temperature (Kelvin) & Mired Converter
Convert bidirectionally between Color Temperature in Kelvin (K) and Mireds (micro reciprocal degrees), evaluate human perceptual color shifts, and calculate photographic filter gel ratings.
Color & Scale Parameters
Standard residential living rooms and bedrooms; creates an intimate, relaxing ambiance reminiscent of sunset incandescent lighting.
Step-by-Step Color Temperature & Mired Derivation Proof
How to Convert Between Kelvin and Mired
To convert Kelvin to Mireds, divide 1,000,000 by the color temperature in Kelvin: M = 10⁶ / T_K. To convert Mireds to Kelvin, divide 1,000,000 by the Mired value: T_K = 10⁶ / M. The Mired shift between light sources is ΔM = M₂ − M₁, where positive values require orange warming filters (CTO) and negative values require blue cooling filters (CTB).
Planckian Blackbody Radiation & Correlated Color Temperature
In optical physics, Color Temperature is defined by the spectral radiant emittance of an idealized opaque physical object known as a Planckian blackbody radiator. As an iron bar is heated in a furnace, it begins to glow dim red (~1,000K), transitions through bright orange (2,000K) and warm incandescent yellow (2,700K–3,000K), becomes brilliant white (5,500K–6,500K), and finally glows deep electric blue at extreme temperatures (>10,000K).
The spectral energy distribution of this radiation is governed by Planck’s Radiation Law:
While incandescent filaments and natural sunlight produce genuine thermal continuous spectra, modern discharge and solid-state LED sources emit discontinuous non-thermal spectra. For these luminaires, the metric is formalized as Correlated Color Temperature (CCT): the temperature of a Planckian blackbody whose perceived chromaticity on the CIE 1931 $(x, y)$ chromaticity diagram most closely matches that of the light source.
Why the Linear Kelvin Scale Fails Human Vision (The Mired Solution)
Although Kelvin is universally cited on consumer light bulb packaging, it has a severe mathematical limitation: the human visual system does not perceive color temperature shifts linearly across Kelvin.
A difference of 500 Kelvin at the warm end of the spectrum creates a massive visual transformation from deep orange candlelight to soft yellow incandescent.
The exact same numerical difference of 500 Kelvin under daylight is subtle and virtually imperceptible to the unaided human eye without specialized instruments.
To solve this problem, British color scientist Irwin Priest introduced the Mired (an abbreviation for micro reciprocal degree) in 1932:
On the reciprocal Mired scale, human visual perception and photographic emulsion responses are completely uniform. A 20-Mired change produces an identical perceptual shift in color balance regardless of whether the base light is 2,000K or 10,000K.
Photographic Filter Shift Formulas & Cinematography Gel Selection
In filmmaking, photography, and theatrical lighting design, optical filters cannot be labeled with a fixed Kelvin rating because the resulting output depends entirely on the incoming source light. Instead, lighting gels are rated by their Mired Shift Value (ΔM):
1. Color Temperature Orange (CTO / 85 Series) — Warming Filters
When converting cooler light (such as 5,500K daylight or LED) to match warm tungsten (3,200K), ΔM is positive. Standard cinematic warming gels:
- Full CTO (Rosco 3407 / Lee 204): ΔM = +137 Mireds (5,500K → 3,200K)
- 3/4 CTO: ΔM = +81 Mireds (5,500K → 3,600K)
- 1/2 CTO (Lee 205): ΔM = +68 Mireds (5,500K → 3,800K)
- 1/4 CTO (Lee 206): ΔM = +35 Mireds (Subtle amber fill)
- 1/8 CTO: ΔM = +18 Mireds (Delicate warmth for portrait skin tones)
2. Color Temperature Blue (CTB / 80 Series) — Cooling Filters
When converting warm tungsten illumination (3,200K) to match cool daylight (5,500K), ΔM is negative. Standard cinematic cooling gels:
- Full CTB (Rosco 3202 / Lee 201): ΔM = −137 Mireds (3,200K → 5,500K)
- 3/4 CTB: ΔM = −81 Mireds
- 1/2 CTB (Lee 202): ΔM = −68 Mireds (3,200K → 4,100K)
- 1/4 CTB (Lee 203): ΔM = −35 Mireds (Mild cooling tint)
- 1/8 CTB: ΔM = −18 Mireds
Comprehensive Color Temperature Reference Scale Table
The table below maps common natural and artificial light sources across absolute Kelvin, Mireds, Decamireds (daM), and typical architectural or photographic use cases:
| Light Source / Illuminant | Kelvin (K) | Mireds (M) | Decamireds | Visual Appearance & Application |
|---|---|---|---|---|
| Match Flame / Candle | 1,850 K | 540.5 M | 54.1 daM | Deep warm reddish-amber; intimate dining accent |
| Warm Residential Incandescent | 2,700 K | 370.4 M | 37.0 daM | Soft warm white; domestic bedrooms & living rooms |
| Halogen / Studio Tungsten 3200 | 3,200 K | 312.5 M | 31.3 daM | Standard film & television studio incandescent baseline |
| Cool White / Commercial Troffer | 4,000 K | 250.0 M | 25.0 daM | Neutral crisp white; commercial offices, classrooms |
| Electronic Camera Flash / Noon Sun | 5,500 K | 181.8 M | 18.2 daM | Direct solar midday illumination; photographic daylight standard |
| CIE Standard Illuminant D65 | 6,500 K | 153.8 M | 15.4 daM | Overcast daylight; sRGB, Display P3 & Rec. 709 monitor white point |
| Deep Blue Clear Sky / North Light | 10,000 K | 100.0 M | 10.0 daM | Indirect open skylight without direct sun; cool high-altitude ambient |
Step-by-Step Worked Numerical Solutions
Problem: A cinematographer wants to balance a 3,200K tungsten spotlight to match daylight streaming through a window (5,500K). Find the required gel shift.
Problem: Evaluate the perceptual difference between a 2,700K warm LED bulb and a 3,000K soft white LED bulb in Mireds.
Color Rendering Index (CRI) vs Color Temperature (CCT)
A frequent source of confusion in architectural and consumer lighting is conflating Correlated Color Temperature (CCT) with Color Rendering Index (CRI):
Measures the spectral hue of the emitted light beam itself (warm amber vs cool blue). It answers: “What color does the light look like when looking directly at the bulb?”
Measures the fidelity with which the light reveals true colors of illuminated objects compared to natural daylight or an incandescent blackbody radiator. It answers: “How natural do skin tones, food, and artwork look under this light?”
A high-quality architectural LED installation requires both: selecting the proper CCT for psychological comfort (e.g., 2,700K for domestic living; 4,000K for focused office work) paired with a high color rendering index (≥ 90 CRI / R9 ≥ 50) to prevent muted, gray, or sickly color rendition.
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