someone could explain? thanks. :sleepy:
The blend of metal halide salts in the arc chamber is what controls the output color.
As the bulb ages it will also color shift upward, typically close to 700-1000K of shift over its life.
The only other thing to affect the output color is filters (colored glass).
Philips makes a bulb with minimum color shift over its life, it is about 4200-4300K the part number is 85122+ (the + is key here).