Thanks for the link to the article, Hallyx, but I'm still not sure how long to leave the tank light on for. Drago, my fish, seems to be a lot more stressed when it is on, so I have considered doing an experiment and leaving it off for the day, just letting natural light be his light source. So far... he seems a heck of a lot happier than he seems to be when the tank light is on.
Frazzle - Thanks for the advice! 8-10 hours of light was what I was doing before, but it really seemed to stress him when the tank light was on, so... maybe it's in my fish's best interest not to have the light on? I wonder if this is because he is new and still adjusting?
I'd love to hear more opinions on this! :)