You’ve got quite a few options when it comes to lighting your growing crop. A basic mantra here is that you’re starting off the growth with low intensity and then transitioning to HID (High Intensity Discharge) bulbs at the right stage.
With recent advancements in LED light technology, many growers are getting wonderful results from using LED as opposed to HID. This is an option to strongly consider given the many advantages such as electrical power savings and heat savings. In examining all of the pros and cons, we could get into a rather technically detailed analysis here going into quite some depth. To sum it up, go with HPS, as HPS is much more powerful and the cost effectiveness of LED’s right now do not make sense.
For the early growth phase while you are waiting for your roots to reach to the bottom of the growing medium (soil cup or rock wool cube), we recommend using a combination of warm and cool white fluorescent lighting. You are looking at about a week’s time for this phase, and this type of lighting helps to insure gentle light that doesn’t over-bombard your seedlings. Be sure to maintain about an inch or so between the lights and the top of the plantings. Once you’ve reached the stage where your roots have grown appropriately – it’s time to upgrade grow medium containers to a larger size pot (Gallon size recommended for this phase.)
Now that the seedlings have grown up, we’re ready to bring out either HID lights or LED lights for the longer term growth. We already touched on the LED option above, so let’s look more closely at the two different types of HID lights that have been effective for growers.
METAL HALIDE LIGHTS – The low blue spectrum light afforded by this type is great for leaf, stem and root growth. Various Wattages for this type of bulb exist (175, 250, 400, 600, 1000), so you will need to choose the appropriate amount you need based on the size of your garden/how many plants you are trying to illuminate. The main rule of thumb is that your going to want to gauge that the light reaches evenly to all areas of your garden for best results. Metal Halide Lights are also used primarily in Veg Stage and keep the plants from stretching as much as HPS lights do.
HPS (High Pressure Sodium) LIGHTS - These are slightly more expensive and brighter than the MHS lights and put out more red spectrum light which is great for the plants when flowering. If you are able to afford them, great, because brighter is better.
These two types of HID lights put out a good deal of heat, so it’s best that you make sure you’ve got proper A/C and ventilation to avoid overheating. A good thing to employ is to use vented hoods for covering your lights. This is great for bleeding off that super hot air that comes right off of the top of the bulb itself and avoids a heat pocket forming.
Since these lights are putting out a lot of heat, you’ve got to be careful to not burn up your precious crop, so maintain a 14 -24 inch safety buffer distance between the tops of your plants and the lights. You can decrease this a bit if you are going to employ automated light movers (either back and forth on simple tracking or a more sophisticated “sun circle” system that rotates around your garden –thereby mimicking the natural movements of the sun. Depending on how much you can afford, you have the potential to get pretty fancy here. A good rule of thumb of follow in maintaining safety for your plant’s health as regards these HID lights, is that if you put you had at plant top level and the lights are too hot upon your hand, then it’s too hot for your plants as well…increase the buffer distance.