Colored Lights

[Photon Guy]

I am doing research into colored lights for this project I want to do. When you switch on an ordinary flashlight it emits a plain white light which is all the colors but Im interested in lights that only emit light of one color. Now at the most basic level having such a light can be very simple, all you have to do with your flashlight is put something on it to make it a certain color, for instance if you want your flashlight to be red you could just fit a red balloon over the end of the flashlight and it will make the light red. To the best of my knowledge that works by filtering, the red balloon filters out all the colors from the flashlight except red and so you've got red light. 

Anyway, I don't want something so simple. Im interested in a special light that only emits a certain color without a filter. I believe they do make diodes that operate like that. Im not sure that's how traffic lights work or if traffic lights use filtering much the same way as fitting a red balloon over an ordinary flashlight but the reason Im asking is this project Im working on, I want to make a special type of flashlight. 

[MigL]

Incandescent sources, like the filament in a light bulb, are very 'dirty'.
The light they emit spans a range of wavelengths/frequencies, in a 'lopsided' Gaussian distribution, peaking at the wavelength/frequency characteristic of the temperature of the filament ( see black body radiation curves ).
What you want is an emission which is characteristic of a specific energy difference, which will give only that specific energy ( frequency/wavelength ). LEDs are one such source, as they emit light at the characteristic energy of their band gap, and are readily sourced in differing colors.
Lasers would be another source, as they emit light based on electron orbital transitions ( again a specific energy difference), but are a little harder to source.