Fluorescence is caused by electrons jumping between orbitas in an atom. Or more accurately, when the electron snaps back to its orignal comfortable orbit.
When exposed to UV light, fluorescent proteins have electrons that respond to UV exposure by sending the electron further out into a higher energy orbital shell. They cannot exist in this state for long and almost immediately release the extra energy in the form of a photon and a little heat.
That's it -- a quantum of energy gets released after exposure to a High Energy UV strike. And we see it one photon at a time !
To make this transformation happen we fluorodivers use intense lights emitting in UV or Blue range (often called 'near-uv"). This torch light is the Excitation Source and it's a very bright blue ! This power overcomes the scene so to bring out the subtler fluorescent emissions we use a yellow Barrier Lens to remove the extra blue.
These are important concepts in fluorodiving: An Excitation Source creates the fluorescence, then a Barrier Filter removes the extra energy from the scene. If one was doing photography one would put the Exciter on the Strobe and the Barrier over the camera lens.
These excitation sources can be created two ways: LED's can be chosen in the specific wavelength you wish to explore or you can choose a high-intensity light source and filter out all the extra light you don't need.
I prefer the second way. LED lights nowadays are particularly bright with a good portion of their light emissions in the Blue/UV end of the spectrum. As well LED's are so energy efficient it's not difficult to drop up to 95% of the original white through a filtering process. There will be plenty of Blue UV left.
Most of all -- filtered light sets allow choosing of wavelengths for your torch to aallow exploration into new return colors or increasing the desired effects.
Consider the following two spectral analyses :
This chart shows very strong emission in the UV spectrum. This light would be suitable for initiating strong fluorescence in the proteins but mostly green due to the narrow spectrum. As well there seems quite a bit of leakage from the Red spectrum that might effect photography.
This filter shows strong response throughout the target spectrum with little waste. A filter like this might show more colors besides green.
Choosing the right filter type is important for your area and preferences. Fortunately companies offering filtered torch-kits have done the work for you and will include at least two filters for you to experience the full breadth of the Fluorodiving experience. Soon more filter choices / matched barrier lenses will become available.
So the excitement and discoveries will continue. Fluorodiving has a very bright future !