Here are 3 pics of my golden nugget mandarin tree.

Its under a growlight in my basement where the temperature during the day is 75-85 (depending on how long the light has been on for), and at night the temperature goes down to 50-60 (depending on how wide I open the window that day).

Over the last couple of days, the leaves, especially the new leaves have started to curl. I figured it was either getting too hot for the plant right under the grow light or the plant needed water (even though the moisture gage indicated that the soil was sufficiently moist).

So I have moved the plant from directly under the grow light and watered the plant. In the 24 hours since I have done this, I dont think the curling has gotten worse but I am not sure it has gotten better.

Your thoughts on the cause and the cure for the curling please.

Looks like wind damage.
Young leaves has not the ability to close their stomata that much as fully developed leaves, so will have a higher water evaporation, and by wind this could lead to excessive water loss and thus imperfect leaf development and growth.

But, if, than the symptomes are less severe and only light, Severe symptomes the leaves are curled more and show very typical deformations at the leaf margin...