I'm assuming that the lighting you are looking for are grow lights, in that case you won't get any noticeable amount of heat for your greenhouse as most lights are either fluorescent or LED, which are both very energy efficient.
A good place to look for grow lights is on eBay. There are many different types there but the cheapest would be the single LED lights that you would solder yourself into an LED light string. If you go this route, remember that photosynthesis primarily occurs at two specific frequencies (about 660nm for red and about 440nm for blue). You will also need more red than blue, the usual ratio varies between 4:1 to 7:1,
http://bioenergy.asu.edu/photosyn/education/photointro.html Also if you make up your own light strings you will need to add resisters in the circuits to insure that the bulbs don't blow prematurely. There are you tube videos showing how some people make up their lights but a lot of them don't bother with the resisters which can be a real gamble.
Here is an LED calculator that can help you determine exactly what is required.
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