I'm not so worried about your light. Tell us about your table.

If it's a flood and drain with large rockwool cubes it should not be running all the time. Sounds to me like your rockwool is staying too wet. A drip system is the only system that can run 24/7 but eveb then you can have problems. Should be running for 15 minute ever 2, 4 or 6 hours or however long it takes to fill the tables.

Getting the heat down will help too.