Rose: yours may be LED's.
But I have had two lasers in my small (6G) Eclipse tank. They are red laser lights. Friend bought the lasers for the tank for my son's birthday (she knew I was getting him the tank) over a year ago. First had goldfish then platies. The port can handle like 6 lights. I only have 2 as it is a small tank!
I can't say they prevented disease or anything
Death, death of goldfish, though it was due to overstocking
and lack of cleaning
with the goldfish and just ineptitude with the platies
They show up great at night. Of course, you can't see them at all during the day. What is cool now is I again have goldfish in teh 6G tank, now that I have a 29G for the real fish
When the big goldfish pass in front of the lasers the flashing is sort of eerie. If you train the lights on interesting decorations, that makes for a nice effect.
But it will not make your fish imortal, or immune, or do anything to cover up for any ineptitude on the part of the owner.