As far as heat goes I can hold the back of my hand to my clip on light which is a 65 watt 6100k flood light on a 6.5" clip on fixture from lowe's for hours and it wouldn't burn me or even get close to hot. I have a digital thermometer in my sump and when the light is off it is a constant 74.5 in my sump. When the light is on which it is set on a timer to run for 20 hours a day 4 hours off once my main DT lights come on after sunrise it only goes up to 75 degrees farenheit. I have calupera and chaeto in my sump. I have the calupera in a seperate rubbermaid bin inside my sump with LR rubble in the bottom and I break it up/turn it once a day. The chaeto I have just floating around on one side and it gets tumbled very slowly this way which is best for chaeto to tumble so all sides get light. If this isn't feasable or possible for you then just make sure to turn the chaeto over also every day and trim dying parts off that don't receive light.
Edit/added: My fuge light was 8 bucks for the clip on shop light and another 7 bucks for the bulb as others said 15$ max. Make sure to get a light that is in the 5000k-6500k spectrum. These have been proven to grow macro algae the best, Sanjay says the 6100k's do the best which is what I use. He found the 5k's to be really yellow and lacking in certain wavelength energy where as the 6100k's seem to be a better cool white and have the most useful PAR.
Another reason I keep the calupera seperate is for the reason fatdaddy stated its highly invasive but grows like a weed, a lot faster than chaeto. If left together the calupera will choke out the chaeto and it won't receive enough light.