REdiculous said:
I have some regular 15w CFLs but they're still kind of big, hungry and super-bright. Maybe I should add a light pole to the trailer and put out more light than the street lamps..heh..nah. I'll do something eventually though.
They are definitely super-bright. I'd say that my taillight using a 15W CFL on the ~50-ish VDC it gets back there is brighter than most car taillights, except for some of the newer LED-array ones. Even when my pack runs down and it's only getting enough voltage to barely stay on it's enough to be at least as bright as older car taillights.
As for "hungry", I assume you mean power-wise. If so, I don't know of any more efficient lighting you could stick on there except for LEDs, which you'd either need a lot of little ones or a few more expensive bright ones to match the light output of the CFL.

The CFLs take about 250mA or less at their rated voltage; I don't recall what mine takes at less than half that voltage but I probably put it in that thread.
You can even use two of them, one with a cutoff switch so that it stays off except when you are braking. I don't know how long it would last being switched on and off like that so often, but they are pretty cheap if you look around for sales.
As for being "big", remember that the more surface area a light has, the better chance it has of being seen. Just being bright does not guarantee being seen. When I used a CCFL transparency adapter from a computer scanner as a headlight, I was much more visible to everyone from all forward angles than with any other light I have ever tried (and will be putting one back on there at some point).
If you want to run the CFL at a lower brightness, you could actually just take an old transformer out of something and hook it's output side to the CFL, and it's input to the inverter output. It would probably have to be a 2:1 to be sure of kickstarting the CFL, so that it gets at least around 50V out of the inverter's 120VAC output. If the inverter is lower output than that, it'd have to be a ratio that gives that 50V or so.
If you wanted to get complex with it, you could make switchable ratios, so that it starts at a higher voltage (50V or above) to kickstart it, then switch down to only about 30-36V for minimum output before it shuts off. Problem is that every time it shuts off you have to switch back to the higher voltage to start it again.
Or optionally, just color it with a red permanent marker and/or wrap in red clear party wrap before you stick it in your red taillight housing.

Or use window tinting on the inside of the housing lens, in enough layers to cut down the brightness to the desired level.
I have seen blue / UV CFLs, but not other colors (besides white variations), however if they do make them you could just use those and they'll probably put out less light to start with, then filtering them further with your taillight lens/etc to cut more.
THe disadvantage to CFLs is that they are fragile. I have had one fail in the taillight; I'm not sure why yet as I still haven't gone back to open it up to check why. It's replacement has not failed yet, but I also haven't ridden that bike in months due to the chain alignment problems I must redesign parts of it to fix.
