Light
let there be light!
Choosing your light is one of the most important factors in your cannabis grow and the amount of light provided is directly related to the amount of yield you can expect. This may also be your largest cost associated with growing so it is important to not over do it. Too much light will add unwanted heat to your grow room and can cause heat stress to the plants if not kept at a safe distance. The goal here is to determine the best wattage for your specific grow room.
DIFFERENT LIGHT TYPES
There are basically three different types of indoor grow lights. High Intensity Discharge or HID, LED and Fluorescent.
HIGH INTENSITY DISCHARGE (HID)
High Intensity Discharge or HID lights have two main kings. Metal Halide or MH and High Pressure Sodium or HPS. While either of these lights can be used for the entire grow cycle, the MH is best suited for Vegetative growing and the HPS is best suited for the flowering phase due to the different spectrum of light they put out.
HID lights are the most common and have been industry standard for years. The produce large yields consistently and and provide superior light intensity to other types of lights. The downside of HID is that they also produce a lot of heat which needs to be accounted for in your grow room environment. They are also the most expensive to run, so sizing them properly is very important.
HID grow lights come in several different wattages. 150W, 250W, 400W, 600W, and 100W are the most common. The wattage of the light will determine the maximum possible yield you can achieve. It will also determine the size of your canopy as larger lights will give a larger light area.
The larger the light the more heat they will put out and anything larger than 400W should be put inside air cooled hoods that can be connected to an exhaust fan to pull out the excess heat.
WATTAGE, COVERAGE AND YIELD
A 150W HID light can cover approx 2 x 2 area and are generally used for cloning and seedlings. These lights are too small for mature plants and will only provide minimal yield.
A 250W HID can cover approx 3 x 3 area and will produce between 4 - 6 ounces per light.
A 400W HID light can cover approx 4 x 4 area and will produce between 7 - 10 ounces per light.
A 600W HID light can cover approx 3 x 3 area and will produce between 10 - 16 ounces per light.
A 1000W HID light can cover approx 3 x 3 area and will produce between 17 - 26 ounces per light.
LED
LED lights are favored by a lot of growers due to their lower operating cost and the fact they produce very little heat. In the past, LED lights could not provide the same yield as HID lights but modern LED lights can and will produce equal if not better yields than HID. They are much less expensive to operate but you will pay significantly more up front for the light. When it comes to LED lights generally you get what you pay for so don't skimp.
LED lights come in a variety of sizes from small 13w to very large 2-3000W lights. LED lights do not produce the same yields by watts as HID lights so you will need to provide much larger watt lights to get similar yields. Most LED light manufacturers will provide a wattage conversion or a yield per watt specification so do your homework.
FLUORESCENT
Fluorescent lights come in several different sizes and are generally used for cloning and seedlings because they do not produce enough light intensity to provide full dense flowers. Some modern High Output (HO) fluorescent lights will provide higher light intensity but because of the small coverage area you will need multiple lights to achieve the same outcome as an HID light.
WHAT IS THE IDEAL AMOUNT OF LIGHT FOR CANNABIS
Cannabis plants need between 40 - 60 watts per square foot depending on type. Indicas do well in the lower range while Sativas do better in the upper range. Since most cultivars today are hybrids the genera rule of thumb is to shoot for approx 50 watts per square foot of canopy.
HOW MUCH LIGHT DO I NEED?
To determine how much light you need. simply multiply the square footage of your canopy (the actual area of the plants) by 50w per square foot. So a small 4 x 4 grow tent would have 16 square foot of canopy (4 x 4 = 16) and the ideal wattage would be 800 watts.
Since HID light do not come in 800W you choose between the 600W and the 1000W light keeping in mind that more light will produce more heat and will cost more to operate.
