I like to use the Slimline lights. They are easily concealed and provide excellent lighting. I suggest mounting on the ceiling in the front part of the cage because they are hidden from view. Plus the light that emits from it will cast down and towards the rear of the cage as opposed to blinding you as you look in. I get them at Home Depot, about $20 a pop. The size of the Slimline will depend on how much light you want, depending on the type of critters you are housing. A 23" Slimline in a 48" L cage will be very lit up, but will be ok if the decor seems to accept it. Otherwise I would suggest going with a smaller size. Hope this helps!