BU bulb in a base down socket

[cizzle21p]

Why does this matter? We had to use a BU, PS 400W bulb in a lighting fixture that has base down socket. Any info would be great, just curious as to why it matters.

 

[zbang]

Two things- heat dissipation and light center. Most base-up lamps have less distance from the light/heat producing part to the end of the envelope and correspondingly have a longer support structure to the base. When you burn a BU as base-down, the top of the envelope will get hotter and usually fail faster.

An offshoot of that is that the light center may be in a different place, not in the center of the reflector, so the fixture will produce less usable light.

 

[hillbilly1]

Is this an up light fixture? (shines upward)

 

[cizzle21p]

Up light Fixture

Up light Fixture

This light fixture shines down over a roadway at about a 45 degree angle. The socket is a base down fixture though. We had to use a BU bulb because that is all we have in stock and are unable to get them immediately. I know its not an issue, and assume the lamp would work fine ( for a shorter duration than expected). I was just curious about the details as to why the bulbs are designated for different sockets. Thanks for the info.