Enigma lamps (or "bulbs" as we tend to say these days) are shorter than modern lamps. You cannot use modern lamps in an Enigma because they are too tall; they will push through the plastic "lamp window" sheet. Refer to the main Enigma page for pictures of the lamp windows.
Here are two original Enigma lamps and two modern lamps. (By the way, this caliper is from "Avenger Products" of Boulder City, Nevada. It was a great purchase!)
As you can see, the modern bulbs are close, but they are just too tall.
Now the question everyone asks is "Where can I get bulbs for my Enigma?" As far as I can tell, there are no modern sources for these bulbs. A few have been made available on Ebay, but they're incredibly rare.
It may be possible to find some similar vintage replacements. One possible source is "Don's Bulbs". Don has a lot of rare bulbs, and one that might work is called the "#223", seen here. Although these #223 bulbs have the right form factor (E10 socket), they take a different voltage. The #223 bulb is rated at 2.25 volts, and, the voltage on the Enigma bulb is 3.5 volts. If you can lower the voltage a bit on the machine, you might be able to use the #223 bulb. The #223 bulb is a rare bulb and very expensive. At one point they were going for $50 each.
Another factoid: The current draw of the Enigma bulbs can vary from .25 to .40 amps, with the most common being .30 or .35 amp. 
There are some other options which might work. I've been experimenting with some modern bulbs that have some additional glass at the top of the bulb. I've been able to grind down the top of the bulb without opening it up such that it was small enough to use in the Enigma without causing damage to the lamp window. I don't know how well this would work for other machines, but I may experiment with this method a little more.
It may also be possible to use an LED bulb. I've seen a few that look to be short enough, but I have not purchased any, so I cannot say for sure.
One day a friend of mine and I decided to try to take some modern bulbs and heat them to the point where we could flatten the tops. We must have tried everything to get the temperature of the bulb to the point where it would be soft, but would not melt or collapse. Nothing worked. Glass is a very strange substance and we were unable to make anything other than a mess.
If you find a good solution, please let me know and I'll post it here.
Copyright © 1998-2010 Bob Lord.