If the HID (?) lights are the only source of light then this is completely practical. I often do it in my propagator so it stays warmer at night.

a) Are you in every minute of the day? I guess some people are, but the lights still stay on when you go shopping, pick up the kids, or whatever, right? And I'm guessing you are home at night? You could add a smoke detector in that room for added piece of mind but these lights are pretty safe if you keep combustible materials away from them. Remember to replace the bulbs on a timetable so that they are unlikely to fail on you.

b) You might want to stagger the night shift so that you can see the plants at a convenient time, perhaps in the evening.

c) The plants will only get confused if you let them have natural light during the day and artifical light at night. I don't grow orchids but many plants will not be happy without a clearly defined day and night.

Thanks shrubs and bulbs. Yes, I'm home a lot, almost enslaved by the Orchids and Bromeliads.;)

Yesterday I took a min/max reading of the thermometer, with a low of 16C and hgh of 34 C, so I think we'll keep it where it is for now. I know we could open the door at night, but somehow, growing those pretty orchids (all vandaeceous types) in the light at night sounds wierd, and I have a gut feeling they won't be happy if this plan was put into action. A lot of them are in bud/spike now, and very vulnerable to any abrupt change.

Carol