There are many different types of grow lights and grow light bulbs on the market. Different factors will affect which grow light bulb is best for you. The two main factors you should consider are wattage and spectrum.
Figuring out the wattage you need will depend on tent size, plant coverage, and light type. The last one is important to remember and not all light wattage is created equally. A 200W HID delivers lights much more efficiently than a 200W CFL.
As a general rule of thumb, you’ll want a minimum 23-30 watts of light per square foot. If you have a grow space that is 4’ by 4’ you’ll want at least 400 watts to fill the space. Since fluorescents are weaker you’ll times that by 5, so 115-150 watts per square foot.
Color temperature has a strong influence overs plants and different temperatures will affect plants in different ways. A blue or bright white found in the temperature range of 5000 K is recommended for plants in the vegetative stage as it keeps them short and bushy.
The temperature range around 3,000 K that produces a yellow or red light is strongly recommended for flowering plants. If you can only afford one temperature for the entire growing period, it’s recommended to stay in the lower range of 3,000- 4,500 K.