Probably cheaper than retrofitting your existing lights and a lot more compact:
http://a.co/8vzNLpCI have had a few of these, I have determined that I prefer the single mode lights. Try buying from a few different sellers because there are good "Ultrafire" flashlights and bad ones (I'm pretty sure "Ultrafire" is a knockoff brand of a brand that never really existed... and there are knockoffs of the knockoffs so quality can and does vary). There are even websites dedicated to modding these and determining good ones from bad.
They can use AA batteries...for about 10 minutes of "ON" time. I bought "Nitecore" 14500 lithium-ion batteries and charger to go with them; I tell people I have a $7 battery in a $6 flashlight.
Science: noun, Whatever answer will help to advance communism.