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Grow Lights


New Member
Don't use regular incandescent bulbs ("grow bulbs") or halogens to grow cannabis, this type of light generates huge internode spacing, poor vegetative growth, skimpy yields, and could set your grow room on fire due to the dangerous amounts of heat these lights produce. Spend your money wisely, invest in Fluorescent lighting (good), or High Intensity Discharge lamps (HID-- recommended). HID lighting such as Metal Halide (MH) or High-Pressure Sodium (HPS) supply the high-intensity light that cannabis needs for good growth and large buds.

Added technical information why halogen lighting is a poor choice for plant cultivation by wannabee2004:

Q: Do halogen bulbs have a good spectral output for plant growth?
A: No, the spectral plot output of various halogen bulb types is by far the worst.

Q: Are they efficient at generating useful light for plant growth?
A: No, the best floro/hps/mh lighting each being approx 5X more efficient at plant growth than halogen.

A good way to measure plant growth efficiency of different types of lighting is PAReff. PAR stands for Photosynthetic Active Radiation: the wavelength range of light between 400 and 700 nm that can be absorbed by leafs for plant photosynthesis. PAReff is the PAR/Watt efficiency ratio over a certain area.

Some examples:

Philips Advantage Fluorescent, 5000K: 1.44 PAReff

Philips High Pressure Sodium deluxe: 1.38 PAReff

Philips Dense-Line Emitter Metal Halide, 4100K: 1.38 PAReff

Philips Spot Halogen Masterline, 2950K: 0.263 PAReff

People usually choose halogen for the "low startup" costs of a halogen light. The real costs of halogens result from its low efficiency. 500 Watt halogen lighting produces about 0.08 Watt/s/nm in the green-yellow spectral region which is about the same as 80 watts of cfl's. A 500w halogen grow will cost approx $63 for electricity, whereas a more efficient light source generates the same par value for around $10 (depending on your local prices).

Source, 420 magazine


New Member
I found this great guide for MJ lights that you might want to check out:

Marijuana Lights or grow lights enable the grower to extend their growing season to the whole year. Marijuana lighting also give growers a large amount of flexibility in the growing process. Because the marijuana grow cycle is dependent on the hours of light the plants receive, artificial lights enable the indoor grower to begin the flowering process whenever they want. There are naturally disadvantages to using grow lights to grow marijuana. They often cost quite a bit especially the good ones. Also there is the cost of the electricity. Growers usually use either MH (Metal Halides), HPS (high pressure sodium lamps) and Fluoros. As a rule of thumb, MH work best in the vegetative period and HPS work better in the flowering phase. A combination is often used. Fluoros do work, however they are usually in commercial marijuana lighting.

Read below for a more detailed knowledge.

The amount of light that marijuana receives determines the quantity and quality of the plant and buds. The photo period is the number of light hours verses dark hours in 1 day.Marijuana usually needs 12 hours of dark each day to begin flowering.

Under continuous light Marijuana will grow but will not flower and produce buds. Darkness makes the plants produce flowering hormones and regular undisturbed darkness will make them stop growing and start flowering.

Outdoors the seasons control the photoperiod. As the summer comes to an end and the nights become longer cannabis flowers ready to produce seed. Indoors you control the photoperiod so you can start flowering whenever you wish.

Sunshine is more intense than any artificial light and is free. However some places on earth just don't get enough. Greenhouse growers can supplement sunshine on dull days with electric lights hung in the greenhouse.

The most efficient types of marijuana lighting are sodium or metal halide high intensity discharge (HID) lamps. Metal halides are strong in the blue spectrum of light and are good for growth. Sodium lights are strong in the red spectrum of light and are good for flowering.

High intensity lights also come with different shades. All combinations work OK but its best to use sodium bulbs in horizontal shades for flowering. Plan on giving 30 to 60 watts of light for each square foot of growing space.

Lights get hot and can burn plants that get too near. However the closer the light to the plants the more intense light they receive. In general keep 400 w lights 30 to 45 cm above plants and 1000 w lights 45 to 75 cm above plants.

Fluorescent light is fine for the growing stage but flowering plants really need more intense HID light. If fluorescents are your only choice choose alternate rows of "Cool White" and "Warm White" bulbs and place them only a few cm's away from your plants.

Marijuana grow lights

The purpose of this FAQ is to help limit the spread of misinformation regarding effective artificial lighting systems, and help those who choose to grow marijuana plants under artificial lighting make an informed decision before buying a grow lamp.

Most of the information comes from printed sources, and some from electronically distributed files. Though information also comes from a network of experienced growers who have tried various types of marijuana lighting.

This FAQ is not going to tell you how to use your lamp, that information can be found in most grower's guides.


There are three major types of lighting systems available right now for growing marijuana:incandescent, fluorescent, and high intensity discharge. Incandescent lights are horribly inefficient (especially the screw-in "grow bulb" type) and really not an acceptable option for marijuana plant growth. Although they are inexpensive to purchase, their cost of operation makes them the costliest source of light. Therefore avoid at all costs.


Until the early 1980's most indoor marijuana growers used fluorescent lights to illuminate their garden. These tubes have tremendous advantages over incandescents. They emit about 3 times as much light as an incandescent (given the same wattage), and the light spectrum is one that plants con use more effectively.

However, they do certainly have their limitations. Light is emitted over a large area, so it is not concentrated. Because of this, the lights have to be hung very close to the plants, and constantly moved to accommodate plant growth. This makes garden maintenance rather difficult. Marijuana plants can often grow very quickly increasing the times the lamps need raising. To add to this, in the flowering period, fluorescsent lights are not effective making them a poor choice for lighting marijuana plants.

Fluorescents are, however, very useful in cloning, and starting seedlings. Because in these stages, a plant is not growing vertically very quickly, the disadvantages of moving the lights are reduced. They also put out a more gentle light than the HID lamps, and release less heat.

If you choose to use fluorescents, it is best to purchase the 'cool white' variety or a mix. The ones that are sold as grow lamps (including grow-lux, vitalite, etc.) are much less efficient than a standard fluorescent, and just do not put out enough light to be useful. The slightly different spectrum produced by these lamps does nothing for most plants.

High Intensity Discharge Lamps (HID's)

You will find pictures of marijuana lights here.

High intensity discharge lamps are easier to use, and more efficient. Low wattage HIDs are sometimes sold for household outdoor use. Large Wattage lamps are used for lighting streets, parking lots, stadiums and other large areas. They come in two basic flavors:

Metal Halides or MH lamps emit a white light that looks slightly bluish. They are used to light stadiums, convention centers, gymnasiums, and other large areas where a natural looking light is desired.

High Pressure Sodium or HPS lamps emit a pink or amber light. They are used for lighting parking lots and other areas where the color of the light is not important. HPS units are much more efficient than MH ones, producing more light and less heat per watt of energy consumed. They are often used alone with no detrimental effect on the plants, and will promote faster plant growth than MH lamps during both vegetative growth and flowering. Combinations of
bulbs are NOT required, as the HPS lamp does produce all of the light spectrums necessary for healthy growth.

MH lamps are available in 175,200, 400 and 1000 watt sizes. HPS lamps come in 50, 75, 150, 400 and 1000 watt sizes. Each lamp requires its own ballast, which comes with the fixtures that are designed to use these lamps, and are also available separately.

The following chart shows how much light each lamp emits, and the area that it covers adequately:

Timers for the garden

The lighting system needs to be switched on and off automatically so the marijuana plants receive 18 hours of light per day during vegetative growth and 12 hours per day when flowering. most hard ware stores and other electronic shops sell timers. they are usually very cheap . It may be advisable however to purchase a more robust timer if your serious like a pool timer.

Lamp # of Lumens Sq. Ft

4'FL (CoolWhite-40W) 2,960 1-2
8'FL (CoolWhite-75W) 5,800 2-4
MH 175W 14,000 5-10
MH 400W 40,000 12-20
HPS 70W 7,600 3-6
HPS 150W 16,000 6-11
HPS 400W 50,000 15-30

Marijuana grow rooms should receive 1000-3000 lumens per square foot. Successful gardens usually are lit at around 2,000 lumens per square foot. During the vegetative stage, plants stretch out when they receive low levels of light. During flowering, the flowers are looser and sparse.

When choosing which marijuana lights to use in your garden, we suggest a combination of MH and HPS with flouros used in cloning and early seedlings. It is also important to chose the right shade. Some will reflect light much better than others. Any good supplier should be able to recommend the best for your requirements.
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