Simple and easy. Turn on the HPS for the normal 12 hour cycle and monitor your temperature in the growspace at approximate canopy level. If you don't have temp spikes over say about 83, you should be okay with most strains. If the temp gradually climbs all day to a max of above 83 or so, you will probably want to vent the light outside. Exhausting it indoors around your growspace will still contribute to high temperatures. Must vent hot air outside. Hope this helps.