mercury vapor bulb

[Stormy Rose]

I am using a mercury vapor bulb in my tortoise's enclosure on a zoo med light fixture. I noticed, if you look into the holes around the bulbs base, that there is a brownish stain looking thing on it. It's almost like it dripped as a liquid and dried. Does anyone know what that is, or if that's a sign of a bad bulb???

Thanks!

 

[Yellow Turtle01]

Is the base of the lamp ceramic? Sounds like the bulb's too hot for the fixture!

 

[Stormy Rose]

I am using the Zoo Med PowerSun MVB Bulb (100 Watt) in a Zoo Med deluxe porcelain clamp lamp (8.5 inch dome).
The socket is ceramic too. I am also not using the clamp on the lamp, so the bulb is point straight down.