metal halide bulbs......whats that black color on the bottom....

[raymond4133]

Hey does anyone know why do the bottom of the metal halide bulbs get black....you know near the silver socket where you screw the bulb into the socket....Its right there inside....Someone told me it was a carbon deposit.....

Is there any way with the black deposit can you tell how old a bulb is.....beacause someone just gave me like 5 10K hamilton 175watt bulbs and i tested them and all and they look fine and bright but i am just not sure how old they are.....

Perhaps there is a way to tell with how much black deposit there is....?

please help

 

[raymond4133]

is it me but is it common that metal halide bulbs deveop black on near the bottom if there is a fan blowing....????

 

[PaulErik]

The black coloration right at the base is normal. It's from the manufacturing process. Not all MH lamps are manufactured this way. The black coloration is actually a getter to keep the outer bulb clean of impurities. If it turns white it indcates air has entered and/or the getter material is exhausted.

 

[raymond4133]

so you really cant tell if the bulbs are old or anything.....


How much light or efficeny drops off every year or month....?

 

[PaulErik]

You will not be able tell how many hours a lamp has been used.

You can generally tell if a MH lamp has been used by looking at the inner bulb (arc tube). If the ends near the electrodes are black it's been used for a while. Over time the arc tube usually discolors and can become black to the point where you can not see through it.

Light output drops and color shifts overtime but this greatly varies with different lamps and setups.