im using a 200w fluro grow light. the ballast gives off shit loads of heat, so im using 3 inch computer fans running off 12volts. i bought 2 fans at £3.99 each. The 12 volt adapters cost £5 each

one fan will get placed directly above the ballast to expell the heat, the other fan will be inside to circulate air. I'm using passive air intake

anyway, to get the PC fans to run off mains electric....this is what u do.....like anything...its easy when u know what ur doing