Grow Light Guide
Horticultural lighting systems allow you to extend the growing season by providing your cannabis plants with an indoor equivalent to sunlight. This is a great advantage for those of you who appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting is also a great way to jump-start spring by starting your seedlings months ahead of the last frost. There are three main types of horticultural lighting systems.
In summary, marijuana has a lust for light. HP sodium lamps produce 20% more light than super metal halides. Horizontal reflectors yield up to 40% more light than vertical reflectors. Hammer or pebble specular, anodized aluminum or white are the most reflective surfaces for hoods. Mirror finish is the absolute worst reflective surface for a hood. Hang 400 watt lamps at 18-24 above garden, 600 and 1000 watt lamps, 24-30 above garden. Use a light meter. Grow the strongest, healthiest cannabis plants that reach their maximum potential for resin production. Bright light brings big buds.
HID (High Intensity Discharge) Lighting
HID lighting is the most efficient way to convert electricity into light that is available to the consumer. There are two types of HID grow lights used for horticultural lighting:
HID Light Efficiency
Metal Halide – MH
Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes cannabis plant growth and is excellent for green leafy growth and keeping cannabis plants compact. It is the best type of light to be used as a primary light source (if no or little natural sunlight is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with fluorescent lights and 18 lumens per watt for standard incandescent bulbs.
High Pressure Sodium – HPS
High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in cannabis plants to increase flowering/budding in cannabis plants. They are the best lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.
Not only is this a great flowering light, it has two features that make it a more economical choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in the blue spectrum.
If a gardener were to start a young cannabis plant under a HPS bulb, she/he would see impressive vertical growth. In fact, probably too impressive. Most cannabis plants would grow up thin and lanky and in no time you will have to prune your cannabis plant back before it grows into the light fixture. The exception to this is using a HPS light in a greenhouse. Sunlight is high in the blue spectrum which would offset any stretching caused by HPS bulbs.
Common manufacturers of metal halide and high pressure (HP) sodium lights include Philips, General Electric, Iwasaki, Venture, and Osram/Sylvania. Many of the manufacturers buy and use the same components, often manufactured by competitors. Most often the bulbs have the exact same technical statistics.
Any part of the plant that is further away then 1-2 feet from the fluorescent grow lights is not getting an optimum amount of light, especially in the flowering stage when plants need a lot of light to produce buds.
The great thing about fluorescent grow lights is that they don't get very hot, and they can usually be kept 1-4 inches from the tops of the plants at all times without having to worry about burning your cannabis leaves or buds.
There are many different levels of fluorescent grow lights including the T5, the T8 and the T12. I strongly suggest sticking with the T5 style of fluorescent grow lights for cannabis because they give off the most amount of light for the size, and are specifically designed to be able to support taller plants up to 24 inches.
For flowering, choose bulbs that are "Warm White" or "Soft White" colored (usually labeled as "2500K" or "3000K").
However, you can use either type of lights during either stage and still get good results. People also use "Daylight" (5000K) bulbs with success.