Why do metal halide lamps shift in colour in use and can it be prevented?
A Low supply voltage or incorrect ballast tapping can under power the lamp and produce a noticeable colour shift. Also there is a slow diffusion by some of the metals through the quartz arc tube, changing the metallic mixture and hence the colour of the lamp. This problem has been overcome by making arc tube from polycrystalline alumina which prevent diffusion losses and ensures colours stability throughout life.
