Light as close as possible??

I did my first grow not long back, It was a quality smoke, I grew 4 white rhino, and 4 orange bud.....only problem is, I didn't get much yeild.

The grow went pretty good all the way through, so I'm not thinking it was anything to do with the nutes?? 2 of the plants were a lot taller than the rest which meant I couldn't get the light as close to the others as I'd have liked, would this be the cause of my small yeild??

It may be worth mentioning that it was done over christmas so the temps were a bit ropey at night (in an attic)

What kind of lights did you use, and how many?

I only grew the 8 plants and I used one 600 watt HID and ballast, the dude in my local hydro shop said it would be cool