Take a wander over to the LED section, have a look at some of the grows in the DIY quantum board thread, have a look
@lukio 's journal if you can find it. Check out
@Moflow 's plants if you can find some pictures.
LEDs are great but not all are equal, you don't want a cheap blurple light. Almost all of us use white light like COBs or Quantum boards or other highly efficient strips or boards.
The key is how efficient they are, they are not magical, watts equals heat, so we aim to create the same or more light per watt than HPS counterpart in doing so we have less heat.
If you want a great example of what can be done with the right LEDs go on youtube and check out growmau5, he's a DIY light enthusiast as well as a great grower, check out his early vids, see the quality and weight he is pulling.
If you want to buy DIY kits or ready built units there are a few good sellers on here. A great example for your 5x5 would be a HLG550 or HLG600 from horticultural lighting group or growers lights... The 550 is 550w and matches a 1000w HPS, that's your heat almost halved right there...
Edit, I notice your asking someone about mars lights. That's exactly the kind of light you want to stay away from, no point switching to LED unless its more efficient than your current set up.