Hi,

You might also get some good answers from the folks in the Citrus forum but I'll do my best. Meyer lemons are notorious for dropping leaves when brought inside. They are very picky about changes in light levels. Next year when you bring it out you should first leave it in full shade for at least 2 weeks, then partial shade for 2 more before going to full sun. Do the reverse in the fall.

I wouldn't give up hope yet. A citrus can rebound from a total leaf drop if you take care of it. If you don't have it in a sunny south facing window, supplemental light would be helpful.

I don't have any experience growing under LEDs, but I get the impression that you need to spend good money to get a worthwhile setup. Unless heat generation or electricity use is a problem HID lamps are usually the most cost effective for primary light sources. Another economical option is usually sunlight + several CFLs. If you don't mind paying up, LEDs seem promising. I just have no info on specific LED setups.

Keep in mind, I've overwintered a lemon(unknown variety) with no supplemental light for a couple years so a grow light isn't necessary. My tree does go mostly dormant without extra light.