Mary,
I think the bulbs that are used, are special flash bulbs, similar to a bulb used for a strobe light, but smaller. As for the amount of lumens a flash bulb emits, I'm not quite sure. There are two ways to find this out:
1. You can get or make a light meter to find the amount of lumens the flash has.
2. you can search Google.com for camera flash bulbs. They should explain the number of lumens the flash emits.
If you're stuck on LED's, you can probably get away with making a flash using LED's, but you would probably need quite a few LED's to get the same performance as a flash bulb. I'm not sure what wavelength, or spectrum of light the LED's would emit. If the spectrum of light from LED's is different from that of a flash bulb, you may get some slight discoloration, or yellowing of your photos.
Another option is to hook up a halogen light. It wont flash, but you can turn it on before you take the picture.