PAR or temperature?

If you don't add CO2, that's a bit warm. Not sure on break-even with the extra light... depends on if you are near cap already for DLI -- see DLI chart in my profile comments. convert your lights umol/s per your area^2 to umol/s per m^2 and that's "ppfd" portion of table. DLI is found by hours you use the light per day. But, if already near the cap sans CO2, no reason to add the heat. if not... What about on for 30mins, off for 30 mins? or 15m intervails.. in ratio to get any amount of extra hours worthwhile to get without damaging the plant.