Moonlight.
At first I used this cheapy bulb, but didn't really like it that much.
Then when I was on vacation in the states I found a 13watt PC "party" bulb for sale. It is a blue bulb that seems to have its output centered at aroun 440 Nm or so.
It is more then bright enough for a moonlight, has lasted more then a year, and actually flouresces the zoos a little!
It was actually a little bit too bright, so I set up a small light blocker and all works well.