What type of reflector?

My main issue is keeping room temp constant in a 16 square feet room…
Which reflector in a HPS 600watt or might help keep temp more constant?A sealed or unsealed?

Sealed will keep the temps down when the lights are on, open will allow the heat from the light to fill the room, potentially causing a great difference between “night” and “day” temps. Sealed units usually have fresh air coming into them from outside the room and then push the hot air through ducting to outside the room so very little heat can build up in the room. A 16 sq. ft. room (4’x 4’) with only one 600 watt HPS is a good fit, but it can get hot if the room isn’t well ventilated.