Natural sunlight is free and provides the full spectrum of light wavelengths that plants need, so if you have a sunny window or a sunny spot on your patio, put your plants there. If you are growing inside, you may even want to remove any window screens to allow the maximum amount of sunlight into the room. For most plants, the sunlight needs to be direct, so in the northern hemisphere, a north-facing window will not be adequate. If you are growing outside, consider that direct sunlight may be too strong for certain plants. For instance, lettuce may do better under a 30-50% shade cloth during the hot summer months.
If you don’t have access to a sunny spot, you will need to use artificial lighting. There are 2 types of bulbs: low-intensity (fluorescent and LED) and high-intensity (metal halide, high pressure sodium). High intensity lighting uses a lot of electricity and gets very hot, requiring significant ventilation. For the casual home grower, I recommend using either fluorescent or LED lighting.
Fluorescent light fixtures are cheap and readily available. Most older fluorescent fixtures will fit T12 or T8 bulbs, but for growing plants, you should consider the T5 fixtures and bulbs which have a higher output. Note that T5 bulbs will not fit in the older T12/T8 fixtures. You can use 4100K ‘cool white’ bulbs or 6500K ‘daylight’ bulbs. These bulbs do not produce much heat, so they can be placed within 6-12 inches of your plants for maximum plant growth. It is best if your fixture has a reflector, so that the maximum amount of light is directed down to your plants. If you are only growing a few plants and want a smaller light, consider a Compact Fluorescent Light (CFL) bulb.
LED grow lights are another good option. These lights incorporate LEDs of different wavelengths into the same fixture, to ensure that your plants are getting the full light spectrum. I have had great success using a 200W LED light fixture. Be careful if you are using this type of light inside your home where people will be, since this light emits an intense purple color that can be tough on the eyes.
In deciding the amount of lighting to provide, consider the ongoing costs of electricity to run the light. A 4-foot, 4-bulb T5 fluorescent fixture will use 216W, and the LED fixture mentioned above uses 200W. Where I live, electricity costs about 17 cents/kW-hr. This means that it costs me 3.4 cents every hour I run the LED light. This doesn’t sound like much, but it adds up quickly. If I run the light for 16 hours a day, 30 days a month, this will cost 16 x 30 x 0.034 = $16.32 per month.
To save on operating costs, I have positioned my plants in a sunny window, but I have also placed an LED grow light above the plants for supplemental lighting. The plants get direct sunlight for about 3 hours every morning, and then I turn on the grow light for 5 hours in the afternoon. This combination gives me decent growth with lower expenses.
How many hours of light do the plants need? 12-16 hours a day is ideal, simulating those long summer days when the plants naturally grow like crazy. You can certainly get away with less hours of light, but the plants will grow more slowly. I recommend NOT running your lights continuously for 24 hours a day. Plants have evolutionarily adapted to a daily cycle of light and dark, and it is detrimental to their health to never let them have a dark “resting” period.
If you are installing lights in your room, there are several ways to hang them. The first method is to drill hooks into your ceiling. Make sure that the hooks are drilled into the wood studs, not just into the drywall. This method works well if you are sure that you won’t need to move the lights to a different location. You can then hang the lights using a chain or a rope. It is useful to be able to raise and lower the height of the light, depending on the size of the plants you are growing. Keep fluorescent lights as close as possible to the plants; LED lights can be kept a bit further from the plants.
The second method involves making a movable support structure. PVC tubing is a popular material to use, since it is cheap and light, but it will bow if used in lengths of greater than a few feet. It is better to use stiffer electrical metallic tubing (EMT) conduit if you are making a large structure. In my grow room, I constructed a light support using both 3/4-inch PVC and 1/2-inch EMT. The long vertical and horizontal sections are made of EMT, and PVC is used for the corner pieces and the footings. This entire structure can be moved or disassembled easily. If you are interested in making a much smaller structure made entirely out of PVC, here is a useful YouTube video showing such a structure.
Once the lights are installed, many growers like to cover their walls with highly reflective material, so that any stray light is redirected back to the plants. The easiest option is to paint your walls with flat white paint, which results in about 85-95% light reflectivity. Make sure the paint is flat, because glossy paint does not work as well. Another option is to hang Mylar sheeting, which has reflectivity of 90-95%. One of the worst options is to hang aluminum foil, which only has 55-60% reflectivity.
If you are going to use LED lighting, keep in mind that the intense purple light may be easily visible to your neighbors, especially at night. Unfortunately, indoor hydroponics is often associated with growing marijuana, so while you may be completely law-abiding, your neighbors may think you are doing something illegal and notify the authorities. If you would prefer to keep your growing activities private, you can: 1) grow in a room without windows, 2) grow in a room where you have completely covered all the windows, 3) only run your LED lights during the day, or 4) avoid LED lights altogether, and only use fluorescent lights which attract less attention.