MH bulbs do not decrese in brightness as they age, as mercury bulbs do, yet still give a clean white light.
That's not true at all. All HID lighting sources have declining lumen output as they age. HPS has the best lumem maintenance, followed by MH and then MV.
The basic probe start MH lamps have poor lumen maintenance, especially as they near the end of their rated life. However, pulse start and the newer ceramic metal halide systems have pretty well conquered this problem.
Peter
