These bulbs were used back when there was no other option for a very small light source.
These bulbs are not to be confused with a “Wheat Lamp”, named after it’s inventor, Grant Wheat.
Those lamps were designed for underground mining. Here is the Wikipedia Article on the Wheat Lamp.
Yes, this is a heat sink. The question is, were was the heat coming from and how was this used.
(I could be wrong, but I don’t think Google will help you on this one.)
Before I posted that pic I searched the Internet as though I didn’t know what it was. I could find nothing. Congratulations on your voluminous knowledge.
Creepy looking thing, isn’t it? I can’t imagine that they’re terribly durable. It says these were used in electric railroad locomotives… seems like a harzardous cleanup in the event of a collision.
:weary: For some reason I thought you were saying the heatsink was used with the bulb. As odd as that would be.
Of course I was reading things you never said.
I believe we have some of those lamps at my company's other office. They were still being used up until late last year! I was trying to push them toward a more modern cap lamp so as to drop the weight of that darn big battery on their side! Here is a pic of the lights and the charging station at our other office (pic taken 1 1/2 to 2 years ago):
Well this is typical in the mining industry (at least this is what I see and hear). Many things are still done the old fashioned way with old technology. Even when you try to push the new technology as being better, more productive, less downtime, etc . . . they are still reluctant to change! My co-workers now use Li-Ion powered LED cap lamps. I haven't seen them yet, but from what I hear the battery is built into the cap lamp assembly and is charged inside (i.e. battery is not removeable). I think they only put out about 150 lumens (I couldn't find LED cap lamps certified for u-gnd use which had higher output), but they are rated for over 8 hours continuous use which is the most important consideration. I would love to see these new ones and see what the beam is like and what the tint is like. I'm willing to bet it's a very throwy beam with nasty cool white tint! One of the issues is that sometimes (not all the time) the cap lamps need to be "certified" for use u-gnd and therefore your stuck with what is available!
I would think the biggest concern in a mine would be sparks. With all that coal dust and perhaps flammable vapors. Lead-acid batteries just don’t sound that safe to me. I would think that what you would want is an integrated light and battery, perhaps hermetically sealed so that there would be no sparks. Charging would be done above ground.