// Colour temperature to RGB: prints the approximate sRGB white point for 1000 K to 6500 K in 100 K steps.
//
// Algorithm: Tanner Helland, "How to Convert Temperature (K) to RGB: Algorithm and Sample Code" (2012),
// a curve fit to Mitchell Charity's blackbody colour data. It is an approximation for UI work and
// previews, not a colorimetric conversion.
//
// Built by the makers of Sundown for Mac (https://t...content-available-to-author-only...n.com). To compare common night settings,
// try the Blue Light Calculator: https://t...content-available-to-author-only...n.com/tools/blue-light-calculator
 
function kelvinToRgb(kelvin) {
  const t = kelvin / 100;
  let r, g, b;
 
  if (t <= 66) {
    r = 255;
    g = 99.4708025861 * Math.log(t) - 161.1195681661;
  } else {
    r = 329.698727446 * Math.pow(t - 60, -0.1332047592);
    g = 288.1221695283 * Math.pow(t - 60, -0.0755148492);
  }
 
  if (t >= 66) {
    b = 255;
  } else if (t <= 19) {
    b = 0;
  } else {
    b = 138.5177312231 * Math.log(t - 10) - 305.0447927307;
  }
 
  const clamp = (v) => Math.round(Math.min(255, Math.max(0, v)));
  return [clamp(r), clamp(g), clamp(b)];
}
 
function toHex([r, g, b]) {
  return "#" + [r, g, b].map((v) => v.toString(16).padStart(2, "0")).join("").toUpperCase();
}
 
console.log("Kelvin   Hex       R    G    B");
for (let k = 1000; k <= 6500; k += 100) {
  const rgb = kelvinToRgb(k);
  console.log(
    String(k).padEnd(8) + " " + toHex(rgb) + "  " + rgb.map((v) => String(v).padStart(3)).join("  ")
  );
}
 

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