Kinds of Grow Lights
There are several kinds of lights, but below are the four most prevalent ones you'll find in a grow space. There are several variations within each of these four kinds as well, and new lights and technology come out all the time.
Lights have components and bulbs, and some require a ballast. Depending on the type and model, the bulbs or the fixtures can be more expensive. There are a lot of abbreviations, but do not be alarmed.
HID (high-intensity discharge) is an umbrella term under which MH and HPS bulbs fall, which we'll discuss more below. These kinds of lamps have a hood that reflects light and bulbs that are enclosed capsules containing a gas, as opposed to bulbs you 'd see in your house, which have a filament that heats up.
For HIDs, light occurs as an arc between two nodes inside the bulb. The gas contained in these bulbs is what makes MHs and HPSs different. HID bulbs are typically more expensive than the reflective hoods that hold them.
HIDs have been the standard in indoor weed cultivating for decades, however LEDs are quickly catching up to them. Both types of HIDs are usually affordable to buy but will eat up electricity. HIDs throw off a lot of light and heat, which the plants need to grow and get potent. But, they run hot, contain heavy metals, and ballasts can fail.
Nevertheless, because of their low cost, if you're new to indoor growing and not sure how often you'll do it, you might want to invest in an affordable HID light in the beginning to test the water.
MH (Metal halide)
These bulbs contain mercury and metal halides, generate a bluish light, and are commonly used for vegetative growth. They need a ballast to regulate the current. In the past, ballasts have been big and bulky, but digital ones are now available.
HPS (High-pressure sodium)
These HID bulbs typically contain sodium, mercury, and xenon, and generate a yellow/orange light, and are generally used for flowering plants. Some growers will start off plants under MH bulbs and change them to HPSs when plants enter the flowering stage, using the same hood. These lights also require a ballast.
CFLs (compact fluorescent lamps) are fluorescent lights similar to what you would see in a school or office building, but smaller. For growing weed, they are typically called "T5s"-- the "T" stands for "tubular" and the "5" represents its diameter, "⅝".
There are daylight bulbs and warm white bulbs; the former better for vegetative growth, and the latter for flowering.
These fluorescent lights are cheap and efficient and good for vegetative growth. They're particularly good for helping along germinating seeds and small seedlings since they do not put off much heat and will not burn the delicate seeds. They will not increase your electricity costs too much.
The disadvantage to CFLs is they aren't great for flowering plants, and cultivators will usually use another kind of light to finish plants. CFLs just don't generate enough intense light for plants to pile on weight.
Components are available in all shapes and sizes and can usually accommodate 4-12 long fluorescent bulbs; a standard size is 8 bulbs. Fixtures normally have a reflective material to bounce light in one direction, down on your plants.
LEDs (light emitting diodes) are relatively new to the marijuana growing world, compared to HPSs, MHs, and CFLs, however they are quickly proving to be the way of the future. LEDs may be more expensive to purchase initially, yet they are much more efficient and kinder to the environment and your electricity bill. Some cities even give tax breaks to commercial cultivators who use or change to LEDs because they're better for the environment.
LEDs also typically run a lot cooler than HIDs, so you may not require additional equipment to cool down your grow area, and one LED can usually be used for both vegetative and flowering growth. Some high-end LEDs allow you to change the spectrum for each growth stage.
New LED grow lights come out regularly, but knockoffs abound. There are a lot of inexpensive LEDs that don't generate the best spectrum of light for plants.