I’ve been trying to grow on a professional level for the last year and half. I grow outside in my greenhouse in very extreme conditions. It can be very challenging to grow this way when you don’t have complete control of the environment. The only upside for me, growing this way, is that it’s cost effective. But I’m ready to go indoors so I can have more control when it comes to my grow. My question to you is this: when growing indoors and using lights in veg and in flower, how close should I have my lights? Thank you for your help. — Alfie
Of course, the distance of lighting to plant tops varies depending on the choice of lighting you decide to use, the amount of heat generated by the lights and the amount of plants you grow underneath them. In general, with HID (High Intensity Discharge) lighting—including MH (Metal Halide) and HPS (High-Pressure Sodium)—individual 1000-watt lights should be kept 24 – 30 inches from the canopy; 600-watt lights should be 18 – 24 inches away; and 400-watt lights can be as close as 12 – 18 inches from plant tops. Keeping your room cooler and supplementing with CO2 gas can allow you to place lights a bit closer.
Raise lights if heat at your leaf surface is too high. Use a light meter if you have one, or if not, simply place your hand at the level of the plants under the light. If it seems too hot, raise the light or lower the plants. Bleaching buds, burning leaves or plants stressing out are usually a sure sign that the light is too close. Fluorescent and LED (Light Emitting Diode) lights generate far less heat while penetrating much less into the canopy, so they should be kept significantly closer to plant tops.
In industrial or commercial growing applications, lights can be higher because you are using more lighting and spreading it around. That’s why commercial lighting hoods are smaller, and the hoods you should purchase for growing under just one light need to be larger and direct the light downwardly into a tighter light footprint.
Also, always be sure to either lower the lights and raise them as the plants grow taller, or as an alternative, you can raise the plants towards the light early on and then lower them as they grow. One big mistake I see over and over is that growers install the light too high and then let the plant grow up towards it. This results in long and lanky plants that struggle to hold themselves up and need staking or trellising in order to keep from falling over. It’s a waste of space and time.
Don’t miss our previous Grow Q&A: My Pot Plants Are Hermaphrodites! Now What?