Tips from the MoM group:
Blue photo floodlights (designed for use with daylight balanced color film) are close to the color of lightning and they also operate at a much higher color temperature than ordinary floodlights. Placing blue theatrical gels over ordinary lamps won’t do as well because the lamps are not very rich in blue to begin with.
I got mine from a little shop that sells only lightbulbs here in town called “Light Bulbs Plus”. One caveat, they don’t last as long as regular floodlights, as they’re designed for quick flashes, not to be left steadily on for any amount of time. This is perfect for lightening effects, however, don’t make the mistake I made last year. During the setup process, the light was left on unintentionally for a while, so I burned through my available bulb life in no time. They also get very hot, so be careful where you place them, just in case they do get left on somehow, (as you see, it happens). Take the proper steps to avoid placing them in a way that could be a potential fire hazard.
We also use the 500W photo flood bulbs for lightning (we sell them as a component in our “Lightning Accessory Kit”). Do be sure to get the daylight balanced or “blue” bulbs versus the tungsten bulbs. They are available at most specialty camera stores, but they are becoming a little more difficult to find. They will typically run $7 – $10 and have a life of between 15 – 60 hours. One other word of advice. As mentioned previously, these bulbs get very hot. So hot in fact that they will melt a standard lamp socket that has a plastic housing (as many of the cheap clamp light fixtures do) if left on for too long. With intermittent use (such as for lightning), they might be OK, but be very careful and do not just leave them turned on. The specialized clamp fixtures that photographers use with these bulbs have a high-temp plastic or a ceramic socket housing (should run $15 – $35). Inexpensive ceramic housings are also readily available at home improvement stores and could be used to build your own fixture.