private ColorRGBA lumensToColor(float lumens) {
        /*
        Taken from /Common/ShaderLib/Hdr.glsllib
        vec4 HDR_EncodeLum(in float lum){
        float Le = 2.0 * log2(lum + epsilon) + 127.0;
        vec4 result = vec4(0.0);
        result.a = fract(Le);
        result.rgb = vec3((Le - (floor(result.a * 255.0)) / 255.0) / 255.0);
        return result;
         */
        float epsilon = 0.0001f;

        double Le = 2f * Math.log(lumens * epsilon) / Math.log(2) + 127.0;
        ColorRGBA color = new ColorRGBA();
        color.a = (float) (Le - Math.floor(Le)); //Get fractional part
        float val = (float) ((Le - (Math.floor(color.a * 255.0)) / 255.0) / 255.0);
        color.r = val;
        color.g = val;
        color.b = val;

        return color;
    }
Convert a floating point lumens value into a grayscale color that
represents a brightness.

@param lumens The lumens value to convert to a color
@return A color representing the intensity of the given lumens
jme3-plugins/src/gltf/java/com/jme3/scene/plugins/gltf/LightsPunctualExtensionLoader.java