Hanging light vs resting on tank

[Krogman]

What are the pros and cons of hanging a light fixture over a tank and the same for it resting on the rim of the tank? When should a fixture be hung and how do you determine how high you should have it over the water? Any knowledge or literature is appreciated

 

[tonedogz]

It kind of depends on the type of light and if its water proof or not. If there led's you could put them resting on the tank because they don't produce heat and if there waterproof but they really should be off the tank a few inchs at least. I wouldn't lay halides or power compacts on the tank because of the heat they produce, they would raise the temp. of the water most likely.

 

[Hulka9]

I know for LED's sometimes they can make a spotlight effect leaving dark spots in the tank. Raising the light up 6 inches or so spreads the light and solves the problem.

I have to do that with my 29G. I'm using a 24" LED (tank is 30"). So I'm raising it up to make the light spread to the edges.