They actually do a decent job of it if you just hold them together in a bunch, or hold one in each hand and one in your mouth so you can aim the light all into one pool, like the old EternaLight Rave'n:
Any one of the coloured Ultrafires makes a decent flashlight all by itself. Red if you're feeling sexy, ominous or both, green for maximum visibility, blue for a particularly unearthly look, including that unexpected fluorescence. I really do highly recommend them. Why use a boring white flashlight when you can have something fun instead?
(They also partner well with my...
...elderly "bullseye" flashlight. It's excellent for seeing where you're about to step at night with dark-adapted eyes; the much narrower and far brighter beams of the Ultrafire lights are great for seeing things further away.)
Coloured flashlights are completely unsuitable for some tasks, like reading maps; shine a red light on a multi-coloured map and any markings with no red in 'em will look black. For everyday flashlight tasks, though, why not do it the sci-fi B-movie way?
You can get these lights on eBay for $US9.99 delivered for just a lamp to put into any Ultrafire-or-other-branded SureFire clone, or for less than $US15 delivered for a whole flashlight with coloured lamp. As I said in the fluorescence post, a red, a green and a blue Ultrafire 501B, plus three 18650 lithium cells to power them and a charger, will only cost you about $US50 delivered, for the lot. Pretend you're getting them to educate your kids about additive and subtractive colour, if it helps.
Now I'm going to have to get an infrared and an ultraviolet one, too. Infrared Ultrafires sell for $US20 to $US30 delivered, and their beam will be clearly visible to any digital camera that doesn't have a good IR-cut filter in front of the sensor.
Actually, even cameras that do have such a sensor can see near-IR...
...but only with a long exposure that'll blur moving subjects:
You could cut the exposure time down quite a lot by lighting a small target with a high-powered IR LED flashlight like this, or using a dedicated IR flash (expensive) or a filter on a conventional flash. But you probably still won't be able to use a properly fast motion-stopping shutter speed unless you've got a camera with no IR filter, or make one yourself. (Or pay someone else to make one for you, complete with tweaking the autofocus so it works properly in the new waveband, but that's cheating.)
Ultraviolet Ultrafire flashlights cost little more than the visible-light ones, but the cheap UV models are barely UV at all. They emit a purple light with a wavelength up around 400 nanometres; this excites fluorescence in various objects quite well...
(Image source: Flickr user davecobb)
...but is clearly visible to the naked eye.
"True" UV LEDs exist too; they have an output wavelength of 370 nanometres or less. (I reviewed a Photon key-ring 370nm light years ago, here.) 370nm light is still visible to the naked eye, but is now a faint white (it's not a great idea to stare down the barrel of a bright near-UV LED flashlight, by the way). As the wavelength gets shorter, the visibility of the light from the LED itself, as opposed to whatever fluorescence it excites in other objects, fades away.
Searching for Ultrafire lights with "nm" in the listing currently turns up an alleged 365nm flashlight for $US19.96 delivered.