RGB Color Temperature

Color temperature: Kelvin ↔ RGB

Color temperature puts a number on the hue of a light source, measured in kelvin (K). It comes straight out of Planck's black-body radiation law, where an idealized emitter heated to T K glows with a specific spectrum. Low temperatures read warm (reddish or orange) and high ones read cool (bluish). A few reference points help: an incandescent bulb sits around 2700 K (warm), cool-white fluorescent at 4000 K, daylight between 5500–6500 K, an overcast sky at 6500 K, and blue shade up near ~10000 K. The Sun's surface comes in at about 5778 K. With LEDs you also want to watch the CRI (Color Rendering Index), which rates how faithfully colors render; for homes, anything above 80 is what you're after. The K → RGB conversion usually leans on Tanner Helland's piecewise approximation, good for 1000–40000 K. And computer monitors are calibrated to sRGB D65 (6504 K).

Applications

It shows up in photography for white-balance correction, in residential and commercial lighting design where Brazilian NBR ISO 8995 sets minimum lux and temperature ranges, and in monitor calibration to sRGB at D65. Post-production color grading in DaVinci Resolve or Lightroom relies on it too, as does home-theater TV calibration against the 6500 K reference and stage or film lighting when you need LED panels to match tungsten.

FAQ

Why does "warm" mean low temperature? Those labels come from how the light feels, not from physics. Red and orange light reads as cozy. Physically the relationship is flipped: a higher kelvin value emits more blue, and blue is the hotter radiation.

Is the K → RGB conversion exact? No, it's an empirical fit of a black-body spectrum mapped onto sRGB. Real LEDs and fluorescents never emit a true Planck spectrum, so two lamps with the same nominal K can render colors quite differently. CRI is the number that captures that gap.

What temperature should I use for studying? Aim for roughly 4000–5000 K, a neutral white. Go below 3000 K and you'll feel drowsy; push above 6500 K in the evening and it can suppress melatonin and throw off your sleep.