Metal halide lighting

 

We do not recommend metal halide lighting for indoor growing for several reasons:

• They very warm. Warm enough to damage plants and people.
• If misused, metal halide lighting cause serious safety issues.
• The heat they produce also makes them inefficient compared to other home lighting options. Be prepared to pay a slightly higher power bill. A 600W light kit used for most of the year uses approximately 1,400 kwH’s. Multiply this by the current cost of power to find out the increase in your school’s annual power bill. You can usually expect an increase of around $150/year.
• Though they're likely more expensive to buy upfront, on a cost per use basis LED lighting provides more value.

If you do use metal halide lights, be sure to read the manufacturers instructions carefully. Though it will vary by manufacturer, general tips for metal halide lighting include:

• You must install the lights several away from any combustible surfaces.
• Once turned on, the bulb will take a few minutes to reach its full output.
• If you turn off your light for any reason, give it 30 minutes to cool off completely before re-lighting, as it may not turn on immediately.
• In the event of a power outage, your light bulb will turn off and will go back on when it has cooled enough for the bimetal switch to move up and down according to temperature. It will not physically start if it is too hot.
• Your bulb is likely rated for 12,000 hours and should work great for 3 growing cycles unless it is damaged. If there are any cracks or scratches on your bulb from the manufacturer or a great deal of broken glass on the inside of the bulb, you should replace it immediately.
• If you need to change the bulb, make sure it has cooled down before touching it. Alternately, you can wear gloves to protect your hands.
• Do not use the light bulb if the outer or inner glass looks cracked in any place. There are tiny pieces of minerals inside the inner arc tube. These are necessary and should ideally be face down when the light bulb is screwed in.
• If the glass bulb cracks or breaks when the light is on, unplug the light immediately. The arc tube inside the glass bulb produces ultraviolet (UV) radiation and over an extended period, causes skin burn and eye inflammation without the protective glass bulb.
• Keep the box that the light bulb came in and use it to store the light bulb if you have to remove it from the cool tube for any reason (ex. if it burns out). This will ensure the glass doesn’t break while being handled.
• Your set up should include an integrated fan. A fan helps to cool the light bulb by blowing cool air across it. This is the function of the fan. This will help the cool tube remain even cooler, to prevent injury if the light bulb is touched for an extended period.

Thanks to Little Green Thumbs for providing the information and images on this page.