http://www.cree.com/led-components-and-modules/products/xlamp/discrete-directional/xlamp-xml2

And 

http://www.meanwell.com/search/hlg-120h/default.htm

Hi,

My friends father has a small supermarket and he has a Cold room he like to light up with as many lumen per watt as possible so the heat will be minimal.

I like to make this for him and like to connect 16 PCS of cree XM-l2 in each lamp fixture then hook it up with a suitable driver.

I am not good at this but i like to learn much more. Can i just put the LED in serial and get the 48V driver?

Remember that my friends father like as little heat and as much lm/w as possible from this fixture, he needs 4 fixtures and i am keen on doing a perfect job for him.