Color Temperature to RGB

colorTempToRGB.js

// From http://www.tannerhelland.com/4435/convert-temperature-rgb-algorithm-code/

    // Start with a temperature, in Kelvin, somewhere between 1000 and 40000.  (Other values may work,
    //  but I can't make any promises about the quality of the algorithm's estimates above 40000 K.)

    
function colorTemperatureToRGB(kelvin){

    var temp = kelvin / 100;

    var red, green, blue;

    if( temp <= 66 ){ 

        red = 255; 
        
        green = temp;
        green = 99.4708025861 * Math.log(green) - 161.1195681661;

        
        if( temp <= 19){

            blue = 0;

        } else {

            blue = temp-10;
            blue = 138.5177312231 * Math.log(blue) - 305.0447927307;

        }

    } else {

        red = temp - 60;
        red = 329.698727446 * Math.pow(red, -0.1332047592);
        
        green = temp - 60;
        green = 288.1221695283 * Math.pow(green, -0.0755148492 );

        blue = 255;

    }


    return {
        r : clamp(red,   0, 255),
        g : clamp(green, 0, 255),
        b : clamp(blue,  0, 255)
    }

}


function clamp( x, min, max ) {

    if(x<min){ return min; }
    if(x>max){ return max; }

    return x;

}

Thank you very much!

To anyone asking for RGB_to_Kelvin, this is way more complicated than you think. And there's many algorithms, depending on how we define color temperature.

If I gave you 0x00ff00 (max green), there's no color temperature that's purely green, so the return value should be NaN. The vast majority of RGB values cannot be reliably converted to kelvins