It’s a bulb from a hanging light fixture in our church. I haven’t been able to sort out the bulb options on the many sites to identify this.
Top of Bulb:
300W
125-130V
GE
Extended Service
Box:
300 Watt Extended Service Lamp
FG3579-E
Dimensions:
4" wide by 9" tall
Base slightly less than 1.5" wide by a bit more than 1.5" high (bottom tip to top of brass)
From your description it sounds as if it is a GE FG3579-E 300 watt bulb. 
I assume you’re actually asking about a replacement? How about this one?
That might be the one. I’m a little leery about the definition of mogul base, since I have seen what appear to be different subcategories of mogul base out there.
Anyway, I want a long-life bulb since it’s a real pain to get to these fixtures. They probably haven’t been changed in twenty years.
This one claims 4,000 hours.
What do you mean by ‘different categories’? Like ‘mogul screw base’ and ‘mogul prong base’? Or are you seeing different mogul screw bases?
I went back through the sites I looked at and now I see that Mogul seems to only be shown next to E39. I had seen other Enn numbering, but not labeled “Mogul”
Cool. That bulb you found seems much cheaper for some reason. The dimensions fit, so it’s likely the one. Thanks!
Good luck. Aside from knowing the difference between 5600ºK and 3400ºK, I don’t know squat about lamps!
I just had a really good idea!
Brilliant!
minor7flat5: Have you thought about replacing the incandescent bulbs with fluorescent? I only did a quick search, and was only able to find 42w mogul base ones that replace a 150w incandescent. One claims a 10,000 hour life. Can you accept half the brightness in exchange for 1/6 the power? (And a much higher price, unfortunately.)
Fluorescent in church?
And most fluorescent replacement bulbs commonly available in stores are not meant to be used in an inverted position. The OP didn’t say it was the case, but many hanging fixures position the bulb base up.
Why not? The only problem is that while the light looks normal to the eye, it can be a PITA when you’re shooting a wedding – not because of flicker, but because the colour temperature of fluorescents makes everything look greenish. White balance fixes that, but if there’s sunlight coming in as well (5600ºK) and/or you’re using the tungstens as well (3400ºK) it can get tricky. (Eh, fix it in post.)
Didn’t think of that, and didn’t know it would be a problem. The churches and commercial buildings I’ve been in have recessed overhead lighting, and the fluorescent ‘bulbs’ hung base upwards like the incandescents they replaced.
ParentalAdvisory and GaryM are both right.
It’s mounted base-up. And it would look like crap to have fluorescent fixtures in church. It really would.
The fixtures would be the same ones you have now. I’m talking about the screw-in fluorescent ‘bulbs’. But it might cause problems if you’re videotaping weddings or other events where the lighting can’t reasonably be controlled. Anyway, it was just a thought.
It looks like a GES base to me.
