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Thread: Lighting information guide

  1. #1
    Fallen Cannabis Warrior Medical Marijuana's Avatar
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    Lighting information guide


    One of the most important elements of indoor growing is the lighting with this guide im hoping to cover as much as I can basically for a quick guide for beginners.


    Plants have the unique ability to manufacture their own food. In the process known as photosynthesis, chlorophyll uses light energy to convert carbon dioxide from the air and water from the ground into food sugar.

    When these elements abound in a perfect environment, the production of food is limited only by factors that effect photosynthesis, being the intensity, color and duration of the daily light the plant receives.

    Cool (blue) and warm (orange) colors in the spectrum enhance chlorophyll activity and food production. Cool light is most pronounced during the summer months when the sun is highest in the sky. It is responsible for keeping plants growth compact and shapely. Warm light, such as when the sun is lower in the sky during the autumn harvest months, is responsible for triggering reproduction in plants in the form of flowers and fruits.

    Thus, if you plan to grow mostly leafy crops , your best bet is a MH lighting system. If you want to grow flowering plants, the HPS lamp is your best bet. As a matter of fact, there are conversion bulbs which allow you to buy one type of system and use both types of lamps.

    Conversion bulbs cost more but give you the added benefit of being able to start your plants with the MH bulb, ensuring tight, compact growth, and then switching over to the HPS lamp when the plants are ready to fruit and flower for higher yield.

    High Pressure Sodium lamps emit mainly in the red end of the spectrum and are used principally during the flowering phase however the newer brands are now dual spectrum and may be used for growing and blooming.

    Another great advantage of indoor horticultural lighting is your ability to control the length of daylight thus empowering you with the ability to force flower your favorite strain even when completely out of season. Remember, to grow perfect plants, the secret to the right light is Color, intensity and duration

    Sizes of grow lights

    MH and HPS grow lights come in the following Watt sizes; 50W, 100W, 150W, 175W, 250W, 400W, 600W,1000W and 1500W.(note the lowest hps I know of that you can get in aus is 250w I haven't seen any 1500 w hps either)

    A general rule of thumb for selecting the correct wattage grow light is to determine the size and shape of your garden area. Since grow lights emit a relatively square pattern of light, it is best to consider each light as covering a square of garden. Here is a list of the coverage each size grow light will provide.

    50W = 1.5' x 1.5' or 45cm x 45cm
    100W = 2' x 2' or 61cm x 61cm
    250W = 3' x 3' or 91cm x 91cm
    400W = 4' x 4' or 1.22m x 1.22m
    600W = 5' x 5' or1.52m x 1.52m
    1000W = 6' x 6' or 1.83m x 1.83m

    Light Distance - from leaf surface

    The further away from the lights your plants are, the less total light they will receive. For this reason it is important to keep your light as close to the plant tops as possible, without burning them.

    It is essential that you use good ventillation to circulate the air around your plants. This provides fresh CO2, moves stale, hot air and will help to cool your plants. If using an electric fan to circulate the air, the lights can be lowered closer to the plant tops.

    It is too difficult to suggest exact distances from the leaf surface however with appropriate caution you should experiment bringing your lamp as close to the surface of the leaves as possible without burning or scalding them. approx 300mm is ideal!

    Please note these are only suggestions and you must remain responsible for measuring the effictiveness of light distance. Too close and too quick will burn harshly, remember to acclimatise your plants to the light as you would seedlings to the sun.

    Photoperiod - the amount of time the light is turned 'on

    The beauty of indoor growing is that the natural seasons and life cycles of plants can be artificially manipulated and controlled by altering the photoperiod (the time your light is turned on).

    When your clones or seeds have sprouted, the light cycle should be set for 18 to 24 hours per day. This encourages vigorous growth and is called the vegetative cycle.

    After 4 to 5 weeks (or when the plants are 45cm to 60cm tall and as long as they have lateral branching ) the light cycle can be reduced to 11-12 hours per day.

    A hormone that is present in the plant, senses this change and triggers flowering. Flowering usually takes approx 3 weeks to initiate,and marijuana will usually double its original size from after the light cycle has been changed. It is essential that total darkness covers the room during flowering.

    Using timers

    Regular electrically controlled time switches are essential to ensure photoperiods and adequate air replacement. Electric timers should be used to control the lights and fans.

    IMPORTANT. Unless you have a commercially rated timer DO NOT use more than one light on each timer. Two lights will blow a regular household timer faster than you can blink.

    Manual switching will certainly cause problems when the switch on times begin to vary so don't even think about doing this!.
    For a lot of lights think about setting up relay system(one that can handle larger surges)

    Light Types

    There are five main types of lights that are used to grow indoor plants.


    The HPS lamp produces the best intensity per watt and it also produces an orange like glow that is sometimes compared to the harvest sun. The colour spectrum for the HPs lamp promotes flower production and stem elongation.

    These sodium type lights tend to produce light at the red/yellow end of the light spectrum and some plants can "stretch" and become "stalky" when these lights are used exclusively for growing plants indoors.

    For best results, a combination of both MH lamps and HP sodium lamps will give the most balanced spectrum for vegetative and flowering growth, but either light can be used as the sole light source if you wish.

    Caution: MH bulbs should only be used with MH ballast, and HP sodium bulbs should only be used with the HP sodium ballast


    The MH lamp is one of the most efficient sources of artificial light available to indoor growers. The MH lamps produce the brightest white light available, at a high intensity and at the right spectrum to encourage plant growth. The MH lamps come in either clear or phosphor coated.

    The difference between the two is the clear bulbs have a higher intensity than the phosphor coated bulbs which makes them better for vegetative growth. The phosphor coated bulbs are preferred as an "all-rounder" bulb. The phosphor coated bulbs give off a spectrum of higher yellow, orange and red, which makes them useful for improving flowering and increasing vegetative growth.


    The mercury vapour lamp is the oldest and best-known member of the high intensity discharge (HID) lamps. The mercury vapour lamps are not recommended for horticultural application because they produce most colour in areas that are not useful for plant growth. Also the mercury vapour lamp is the least efficient HID lamp, and consequently expensive to operate.


    Until the development of high intensity discharge lamps, fluorescent light was the most efficient and widely used. Some fluorescent lamps produce a spectrum almost identical to that of the sun, but have the problem that they don't have the intensity to grow high light plants efficiently.

    Light Intensity is important as well as colour spectrum. You can't stare at the sun without damaging your eyes, so you can imagine the brightness that plants require to grow to maturity. The more the total leaf area, the greater the light required to keep the plant healthy.

    Therefore, the low light intensity of fluorescents work best for cuttings, and seedlings, or for supplemental light, where indoor type plants are not getting enough sunlight. By using Fluorescent tubes, to achieve mature growth, plants must be grown as close to the tube as possible, without touching the tube, as this may cause burning of plant tissues.

    The closeness of the tubes is required as each tube only outputs the minimum light required for plant growth (about 1000 footcandles) and if further away from the tube, the output of the light diminishes.

    Always use a Horticultural reflector. Because a fluorescent tube is round, light is traveling in all directions from the tube, and any light traveling upward, or sideways will miss the plants below.

    Reflectors redirect this light in a favorable manner and generally increase the light to the plants by 50% to 95% with any standard lamp..
    The benefits of Fluorescents are smaller internodal lengths, smaller leaves and smaller flowers but more numerous. Plant growth may be slower than expected.


    There are many types of incandescent lamps. Most of these types of incandescent lamps have a spectrum in the far red. They are also expensive to operate and only produce a few lumens (intensity) per watt; therefore they are not really worth using. as the incandescent light does not encourage vegetative growth.

    However Colour corrected bulbs are available such as CROMPTON, and these output around 5000 footcandles, and are suitable for plant growth, they are more suitable for supplemental lighting, where plants already receive some light from the sun, e.g. most indoor plants, and seeds and cuttings can benefit from the small amount of heat they produce.

    Lighting Costs

    One of the biggest questions people are asked is what will it cost me to run my lights.The answer is it will vary from person to person
    To make things a little easier ill give a quick demo.
    hese rates are from Energy Australia who happen to be my energy supplier my kilo watt hour (kwh) rate is 9.71 cents so to make things easier I rounded it up to 10 cents
    1 400 watt light:
    24 hrs left on $28.80 per month
    18Hrs left on $21.60 per month

    1 600 watt light:
    18hrs on is $32.40
    24hrs on is $43.20

    1 1000 watt light:
    24hrs on $72
    18hrs on $54

    Those figures are based on a 400/600 or 1000w light running at 18hrs a day or at 24hrs a day just double triple what ever for more lights

    Lighting Accessories

    Light Rails move lights over the plants slowly to improve growth. These cost around the price of a lamp, but are very effective in making plants bushy, without growing straight up toward the light source.

    A light mover helps you get the most out of your lighting system by evenly distributing the light across your growing area Reflective plastic (white and Black) is excellent for doing the same thing.

    You hang this plastic like a curtain to reflect the light back into the plant growth. NEVER use aluminium foil, or insulation foils, as these are designed to reflect heat, not light. These foils tend to affect the spectrum, and reflect less visible light, and keep your growroom too hot.

    Some mirror films and Mylar are okay, but only purchase it as is recommended by a Hydroponic Store

    What about the heat generated from an HID Light System?

    Higher wattage systems will generate heat and may need to be ventilated with an exhaust blower or air vent. A reflector cooling kit is available to help you customize a heat exhaust setup for your light system.

    During the winter months, you can use the heat generated from your system to heat your grow room. Temps over 30 Centigrade and under 15 Centigrade are stressful to your plants.

    Extremes of temperature will almost certainly cause damage and stress and growth rates will slow down and production will be poor. DO NOT SKIMP ON VENTILATION or you will pay for it by poor production at the end of your crop.

    General Warnings

    High pressure sodium (HPS) and metal halide (MH) lighting systems are high performance units and because of the control mechanisms when switched on they draw an inductive current which can cause problems with normal domestic timers and electrical circuits.

    Before buying or using any type of indoor lighting get professional electrical advice to make sure that what you plan to use is safe for your particular situation. REMEMBER THAT ELECTRICITY WATER AND HUMANS CONNECTED TOGETHER IS A FATAL COMBINATION. (The other consideration is that in the event of an insurance claim if the lights or their installation or operation was not disclosed to your insurance company then any claims on your insurance policy may be denied - before setting up growing lights indoors check your insurance policy)

    Also remember that you don't look directly into the sun so don't look directly into your lights when there on.

    I hope that has covered most of it below are some charts that will help you in choosing the brand of hps/metal halide light you wish to use.

  2. #2
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    Re: Lighting information guide

    I have been using cfls and have recently switched to led but I have heard good and bad things about both can I use both types in flowering my plants........

  3. #3
    420 Member AKgramma's Avatar
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    Re: Lighting information guide

    Quote Originally Posted by Loren View Post
    I have been using cfls and have recently switched to led but I have heard good and bad things about both can I use both types in flowering my plants........
    Yes, you can. Auxiliary CFLs are great to light the sides of your plants to eliminate shadows.

  4. #4
    420 Member zacmac's Avatar
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    Re: Lighting information guide

    That was some great info for the memory bank. I have a question, I am allowed to grow 12 plants in my state. I have 11 females sprouting as i type. I had 12 but the damn cat took one out. I have regular "known" genetics from herbies but I dont wanna risk putting a male in the mix. I had a box of these I bought at a second hand store for $6.00. Along with the some fun along the way im interested if I could get away with growing 3 plants under two long enough to find out? thanks for any info/help