At least 6 inches above the canopy. You could also get some stand up arm lamps at Walmart and face then towards the center and side of your trees. They will be very happy. I use 'LED' because they cost less in the long run and run cool. 100 watt daylight ones.

The ones I got I got at Ikea....

https://www.google.com/search?q=floor+lamps+in+ikea&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjknIi5_urcAhVkwYMKHS5DBoEQ_AUICygC&biw=1344&bih=650#imgrc=wWRYyyC4qTwRKM:&spf=1534196275274

The bulbs I use are these.

https://www.amazon.com/AmazonBasics-Equivalent-Daylight-Non-Dimmable-6-Pack/dp/B01MSMKBG3/ref=sr_1_3_acs_sk_pb_2_sl_1?ie=UTF8&qid=1534196394&sr=8-3-acs&keywords=100+watt+daylight+led+bulbs

MIke

I am going to try Steve's method for my small citrus trees.

Mike, I like those bulbs, I had them over my cuttings last winter.

Thanks for the great ideas! I ended up ordering the larger Aspect growlight. I really wanted something that didn’t look like a grow op in my kitchen bay window... I’ll take a pic once it arrives and is all set up.

Now those are very nice looking lights! One should be good for the top of the canopy of hanging at least 6 inches close. Can't wait to see the set up)