All About Lighting And Electrical


Sep 27, 2006
GrowFAQ Electrical Safety Hazard Warning, The Physical Effects of Electricity
The Physical Effects of Electricity :
Electrocution or electrical shock occurs when an electric current I passes through the body. The amount of current passing through the body is determined by Ohm's Law:
I = E/R I = Current Through the Body
E = Voltage across the body
R = Resistance of the Body
Body resistance is an important variable when considering electrocution. There is a wide variation in body resistance between people therefore the same voltage level may result in different effects. The typical human body has a hand to hand resistance (R) somewhere between 1,000 and 2,000 ohms. Babies, Children and some other people have less resistance.
The current is the controlling factor for Electrocution and Electrical Shock. The threshold for perception is about 100 microamps (0.0001 Amps). Also See Microshock Electrocution Hazards for currents less than 100 microamps. The National Electrical Code (NEC) considers 5 milliamps (0.005 Amps) to be a safe upper limit for children and adults hence the 5 milliamps GFI circuit breaker requirement for wet locations. The normal nervous system reaction to any perceptible electrical shock may cause a person to injure themselves or others, therefore the so-called safe limit does not assure freedom from injury.
The more serious electrocution and shock hazards occur above the let go limits. 99% of the female population have a let go limit above 6 milliamps, with an average of 10.5 milliamps. 99% of the male population have a let go limit above 9 milliamps, with an average of 15.5 milliamps. Prolonged exposure to 60 Hz. currents greater than 18 milliamps, across the chest causes the diaphragm to contract, which prevents breathing and causes the victim to suffocate. No data is available for females or children but suffocation is presumed to occur at a lower current level.
The frequency of the electrical current is as important as magnitude when evaluating electrocution and electrical shock injuries. Humans and animals are most susceptible to frequencies at 50 to 60 hertz. The internal frequency of the nerve signals controlling the heart is approximately 60 hertz. Ventricular fibrillation occurs when 60 hertz current from the electric shock interferes with the natural rhythm of the heart. The heart loses its ability to pump and death quickly follows. Ventricular fibrillation can occur at current levels as low as 30 milliamps for a two-year-old child and 60 milliamps for adults. Most adults will go into ventricular fibrillation at hand to hand currents below 100 milliamps (0.1 Amp).
Humans are able to withstand 10 times more current at DC and at 1000 hertz than at 50 or 60 Hz.. Electro-Surgical equipment operating above 100,000 Hertz pass high currents through the body with no effect on the heart or breathing of a patient. Do you think that Murphy's Law had anything to do with the American power line frequency being set at 60 Hertz and the frequency for the rest of the world being 50 hertz? All of the current limits referred to in the GrowFAQ articles are based on power line frequencies of 50 or 60 hertz.
Electrocution may or may not leave physical evidence of the injury. The occurrence of burns or other skin damage is dependent upon the current density at the point where the current enters or leaves the body. Electrocutions occurring at 110 VAC seldom cause skin damage unless the point of contact is small or the victim has delicate skin. When higher voltages are involved, high currents pass through the body and there is greater likelihood that skin damage will occur. At higher voltages there are often, but not always entrance and exit wounds.
The painful truth :
 This person lost the use of 3 fingers, which took over 7 months to heal. The thing that worries Overgrow / GrowFAQ is the fact that most people don't understand, or believe that most of the time this beast kill's and does so without warning.
 Most Overgrow members wouldn't want to be put into an electric chair, but will climb into one willingly while wiring a room, opening a ballast, building their own ballast’s or other devices, you name it.
 Electricity can and will kill you if you don't respect it!

What are compact fluorescents and how can I use them for growing?
Compact fluorescents are close relatives of the 4ft tube fluorescents, commonly used in shops and schools for their white, soft light that does not cast any defined shadows. These lights are long tubes, usually 4ft long, filled with a gas that releases a photon of light when excited by electricity. The electricity is passed through the tube from the metal sections at either end, thus exciting the gas within and releasing photons of light. These lights must have a 'starter' which gets the light going initially, unlike incandescent which can just be turned on and off without one. Regular fluorescents usually emit 18w of light per tube, and cannot be plugged straight into a wall socket.
Compact fluorescents, on the other hand, are made for use in regular light sockets, and can easily be installed by anyone with basic handyman skills. Compact fluorescents are usually around 8inches long (not including the ballast, which usually adds about 3 inches to the total length) and emit minimal amounts of heat from the globe itself. Most of the heat emitted from a compact fluorescent comes from the ballast. These lights are usually between 8w and 27w, although some variation may occur between brands and uses.
The main reason people choose CF's over regular fluoro's is their compact ability! They are very 'movable' and can be positioned almost everywhere. They put out MUCH more light than their bigger cousins, while using only a fraction of the space.
If you're running a large grow setup, and you're concerned about the spike in electricity, replace your regular light bulbs with compact fluoro’s around the house! They give off the same light, using only a fraction of the electricity. If you're running a HID light, and the electricity increase could kill you financially, or you're just worried about LEO, it might be a good idea to replace incandescent with compact fluoro’s. As an example, a 100w incandescent uses most of its energy giving off heat. If you replace all these 100w incandescent bulbs with ~20w energy saving compact fluoro's, you can dramatically reduce your energy bill, and help the environment at the same time. In fact, I recommend changing all your lights to CF's regardless of your growing situation, as they will save you $$ in the long-term, and save the environment.
The advantage with these lights is that the conversion from incandescent isn't complicated! Simply un-screw the old bulb, and screw in a compact fluoro! Done! You're on your way to energy saving paradise!

Every grower has, or still uses these lights. Although they don’t even come close to the results from a HID light, they do however provide a cheap alternative for a newbie 'dabbling' in the fine art of growing. Instead of spending hundreds of dollars on a HID light, a newbie can purchase a compact fluorescent for a few bucks, and still have money for a coffee on the way home.
These lights are also excellent for starting seedlings and clones, as their cool light will not dry out the soil as fast as an HID. They have a low intensity, and are gentle on newly germinated seedlings, and are great for clones as they wont dry them out oP give them too much of an early blast.
Compact fluoro's are also great for stealth grows, as they can be kept about 1 inch from the plants, and do not require extensive heat ventilation due to their warm operating temperature.
Most lighting stores will sell them, but watch out, prices are very different depending on what type of shop you get them at! As lighting shops only sell lighting equipment, their prices can either be high or low, it really depends on the type of lighting shop it is. A designer lighting shop may end up being much more expensive, as they tend to be more directed towards the upper-class designer type customer, which extra $$ to spend. Hardware’s sell them, but their variety of lights is usually limited. Electricians, and assorted electrical shops will sell them, and this is most likely where you will get the best range and the best prices. My advice to you is, shop around! You won’t regret it when you can save around 30% per light.
For anyone growing cannabis, it is pointless to buy a weak light. Given the option of 8w, 15w and 27w, you would be stupid not to buy the 27watt, as they are more or less the same price. Compare the lumen output of each of the bulbs, different 27w bulbs may have different lumen outputs (depending on the manufacturer) and as with everything, the more lumens the better. You will also be given 2 options, the screw method of fitting, or the bayonet method (push and turn). My preference is the bayonet fitting. Make sure that you choose the right one for your socket! Also, do not choose a regular compact fluoro. Pick the one with the energy saving feature (will be explained why later on in the document). Now, for vegetative growth you should choose the 'cool white' light. This is also acceptable for flowering, but a 'warm white' light will be better as it is stronger in the red end of the light spectrum, which is more suitable for flowering.
Now, this is extremely easy. As these bulbs fit normal light fixtures, you can just dismantle and old lamp to get the cord, plug and bulb fixture. This is ready made, as all you have to do is plug the cord into a wall outlet and screw in a bulb (with the power turned off, of course). This requires no electrical knowledge at all, and is the easiest way to get a cord suitable for a compact fluoro. The cord is simply removed from the lamp, and you are ready. If you feel you are not up to this task, or you do not have an old lamp ready to be destroyed, you can easily make one of these cords with basic electrical knowledge. Hardware’s and electricians will sell you the cable (you'll need at least 1 meter) and the fittings for the wall socket and the light. Just tell them you're making a lamp for pottery and need a few cables to make up yourself. The parts are cheap, and you can save $$$ this way. If you have any queries, the electrical store will know exactly what type of cables you need etc, and will be more than happy to give you instructions on how to put it all together.
Please note that this is a guide for regular compact fluoro's. There are some outdoor varieties (which are rare) that need to be fitted specially. This FAQ is written for the regular compact fluoro’s, the ones that are most accessible to the general population. Other varieties of compact fluoro's are hard to find, but may or may not be better for growing. As I have little experience with these rare lights, I cannot comment on them. The reason I haven't seen them before, is because they are almost non-existent where I live.
To build this reflector you will need a regular soda can, any brand will do, which you will need to rinse thoroughly until no residue is left inside. You will also need a good pair or scissors and a robust kitchen knife to cut the metal accordingly. An alternate method to remove the lid, would be to use a can opener. The lip of the lid can be used, and it will cut it cleanly. These tools should be chosen carefully as they will determine over failure or success of this construction. A lack of caution and a sharp metal edge can be fatal to your fingertips so think twice if your tools are capable of doing the job.

The main advantages of modifying your compact fluorescent are:
 Reduced length of compact fluorescent
 Reduced heat build up (increased air-flow)
 No need for pre-made light sockets, saving you money
There is an even cheaper and more compact solution than to spend the extra cash on unnecessary light sockets and to end up with less usable space due to clumsy fixtures. All these problems can be avoided easily if one knows how to skips wiring a bulb socket and instead going straight to wiring the bulb itself. This requires some adjustments and modifications of the bulb casing but it can be done by simply following the steps provided.
For this example I will use a 23W Phillips fluoro bulb which is ideally used in confined spaces due to its compact size. The following pictures will illustrate the process of re-wiring this bulb and modifying it to meet the requirements of compact size and low cost.
It all depends on what light you are using, if it’s HID, standard fluoro or compact fluoro (I assume you're not using halogens!). For HID (HPS or MH) lighting, use roughly 30w per square foot, and for flowering use around 60w per square foot. This is merely a guide, your plant, light height; reflective surfaces etc make a huge difference on these numbers. For a small plant, below 1ft tall, I’d say you would need at least 25w of fluorescent light. I find that it isn't at all practical to use tube fluoro’s for the vegetative stage past 6 inches, as only the top of the plant is receiving enough light to carry out photosynthesis properly.
Using energy saving compact fluoro will help 'push' the light to the base of the plant, assisting photosynthesis. If the plant indicates it needs more light by growing slowly, and with small leaf petioles, you may need more light. Go with the basic rule of keeping the fluoro’s very close, and using roughly 20-30w per square foot for strong vegetative growth. If you can afford to over-light your grow room, why not? You won’t regret it when your plant is bushy and healthy. If you feel that you need to only purchase a minimum amount of lights, you probably shouldn’t be growing.
Growing takes effort and money, and if you can't support plants needs you might as well just forget growing until you can afford a proper setup. Skimping on lights is the biggest mistake a grower can make, because photosynthesis is so important to for a health plant.
When purchasing a compact fluorescent, you will notice that nearly all of them have a larger number on the box, than what it actually is. This number is the lights comparison to the brightness of a standard incandescent globe. Do not be fooled, this does not mean that the light is 100w! It is most likely around 18w.
Now, here is where the myth behind these lights is uncovered. Most people will say that you should totally discard the brightness rating. This is wrong! The brighter a light is, the more penetration it has. With a usual, run-of-the-mill compact fluorescent (say, 15w) it emits only 15w of light with poor penetration. Energy saving compact fluorescent with 15w of light, which is rated to 100w of light, will only emit 15w of light. The difference between the two is, the energy saving light has a much stronger light penetration of the normal one, while still only emitting 15w of light.
This is beneficial to growers because with a larger plant, a normal 15w compact fluoro will sufficiently light one part of the plant, and by the time the light has reached the other side of the plant, so much of the light has been lost that it is barely worth having. With the energy saving compact fluorescents, the light will travel to the other side of the plant, and still have enough intensity for reasonable results.
Keep these lights under a reflector all of the time to concentrate the light onto the plant. Hang them horizontally, as most of the light is given off by the middle of the tubes. Keep them close to the plants. As a general rule of thumb, 1 inch away from the top of the plant is perfect. Any more, and you're wasting your time, and less and you risk burning your plant (although these lights are very cool, it is possible to burn your plant if it touches the light or ballast for an extended period of time). If you're given the option, go for a few compact fluoro’s positioned around the plant, as opposed to 1 strong light at the top. Positioning lights around the plant help stop vertical stretching, and encourage the plant to bush out.
HID lighting is generally accepted as a better light for growing cannabis for a few reasons...
 It has much better light penetration
 It is much more powerful (higher lumen output)
 It is stronger in light spectrums suited for growing plants
What can we do to combat these problems to make the most out of our fluoro’s?
 Use a good reflector. Desk lamp reflectors are perfect, along with coke cans (cut in half from top to bottom).
 Purchase lights with high energy saving capabilities (e.g. high watt ratings)to increase light penetration
 Purchase lights with suitable spectrum strengths for each phase of growing (e.g. warm white, cool white etc.)
 Keep the lights close to maximize intensity
 For good results, these lights must be used with a good quality reflector. They give of 360 degrees of light (in a 2D cross-section) but you will only really need 90 degrees of light (maximum). Building a reflector will help concentrate all the light to the area needed, instead of wasting it lighting up the ceiling of your grow room!
 Although you can successfully grow and flower a cannabis plant under a fluorescent, your results will be poor and you will most likely be disappointed. Use these lights only for seedlings and clones, and perhaps the vegetative stage of the cycle. A HID light is recommended for flowering.

Jackerspackle's Lighting Coverage Primer

A very general rule of thumb is that your garden needs 50 watts of HID lighting per square foot of illuminated area. This rule ignores the shape of your garden, so the following is really a better guide:
A 250 watt HID will illuminate a 2' x 2' garden.
A 400 watt HID will illuminate a 3' x 3' garden.
A 600 watt HID will illuminate a 3.5' x 3.5' garden.
A 1000 watt HID will illuminate a 4' x 4' garden.
From Jackerspackle, here's a different take on watts-per-square-foot/meter (WPSF).
WPSF assumes that the bulb's intensity is equal over the entire grow area.. in other words each square foot/meter receives the same number of lumens. But in reality light diminishes rapidly the farther you go from the bulb (1/4 the intensity for each doubling of the distance). So each bulb has a limited range, beyond which you do not have good growth.
For example, a growspace that's 2 x 10 feet would require 1000 watts if you go by the 50 WPSF guideline that's commonly mentioned.. But a 1000 watt bulb only covers an area about 5 feet across - meaning the edges of your garden will be dark.. A better choice in this case would be three 400s or two 600s.
Another problem with WPSF is it assumes all bulbs have the same intensity. But 1000 watts of HPS is not the same as 1000 watts of fluorescents or (yuk) incandescents. Fluorescents have their lumens spread out over a long tube and are therefore dim.. incandescents have the wrong color spectrum and are also dim.
Nor is a 1000 HPS the same as four 250 HPSs.. 250s don't have anywhere near the intensity needed to penetrate thick canopy or tall, bushy plants. (Don't even think about growing meter-tall plants with a 250.)
I could go on, but here's a basic guideline for lighting a growspace for good growth using common HIDs:
1000 watt - 4 to 5 feet across (1.3 to 1.5 meters)
600 watt - 3.5 feet (1 meter)
400 watt - 2.5 possibly 3 feet (.8 to .9 m)
250 watt - 2 feet (.6-.7 m)
175 watt - small, less than 2 feet
These numbers assume you have a good reflector around your bulb and also reflective wall coverings. You can increase the figures a bit if using multiple bulbs, due to their overlapping effect. You can also increase coverage using a light mover

What do all of those lighting terms mean?
This glossary will help you understand terms commonly used in the world of lighting.
AVERAGE LIFE - The life expectancy of a lamp, based on laboratory tests.
AMPERE (AMP) - The unit used to measure the strength of an electric current.
ARC - The luminous discharge of electricity between two electrodes in HID lighting.
ARC DISCHARGE - A transfer of electricity across two electrodes (anode and cathode), characterized by high electrode current densities and a low voltage drop at the electrode.
ARC TUBE - The enclosure which contains the luminous gases and also houses the arc.
BALLAST - An auxiliary piece of equipment designed to start and to properly control the flow of power to gas discharge light sources such as fluorescent and high intensity discharge lamps. In metal halide systems, it is composed of the transformer, capacitor and connecting wiring; sodium systems require an ignitor in addition to the transformer and capacitor.
BASE - The end of the lamp that inserts into the lamp socket.
BU - An industry code indicating that the bulb is to be operated only in a base up position.
BULB - The glass outer envelope component of an HID lamp which protects the arc tube.
BURNING POSITION - The position in which a lamp is designed to be operated.
CAPACITOR - An electronic device that can store electrical charge. The capacitor is one of the main components of a HID lighting ballast. Because they can store a very strong electrical charge, capacitors can be very dangerous to someone who is unaware of this fact and opens a ballast in order to examine or repair it. If one does not know how to safely discharge the stored electricity, one should allow a trained technician to do any ballast repairs.
COLD START TIME - The length of time required to bring an HID lamp to 90% light output from a cold condition.
COLOUR TEMPERATURE or KELVIN TEMPERATURE - The unit of measurement to express the color (spectrum) of light emitted by a lamp.
CONVERSION BULB - A bulb of a certain spectrum type (e.g. sodium) specially designed to operate while used in the fixture/ballast of a different type (e.g. metal halide). The most popular conversion bulbs by far are sodium conversion bulbs, which allow one to have the sodium spectrum while still using a metal halide system.
DOME - The portion of a HID outer bulb located opposite base (the neck and threads).
DOME SUPPORT - The spring-like brackets, which mount the arc tube within the outer envelope (bulb).
DISCHARGE LAMP - A lamp that produces light by discharging an electric arc through a mixture of gases and gaseous metals.
ELECTRODES - Filaments located at either end of a discharge lamp that maintain an electrical arc between them.
FIXTURE - The electrical fitting used to contain the electric components of a lighting system.
FLUORESCENT LAMP - A discharge lamp in which a phosphor coating transforms ultraviolet energy into visible light. Fluorescent lamps are good for starting seedlings and rooting cuttings, but do not have enough intensity to sustain aggressive growth in plants in the later stages of life, and are not efficient enough in their conversion of electrical power to light output.
FREQUENCY - The number of waves or cycles of electromagnetic radiation per second, usually measured in Hertz (Hz).
HALOGEN LAMP - A short name for the tungsten-halogen lamp. Halogen lamps are high-pressure incandescent lamps containing halogen gases such as iodine or bromine, which allow the filaments to be operated at higher temperatures and higher efficacious. While excellent for home lighting and similar applications, halogen lamps are not effective or efficient as grow lights due to their very poor spectrum (extreme far red) and high operating temperatures.
(HID) HIGH-INTENSITY DISCHARGE LAMP - A general term for mercury, metal halide and high-pressure sodium lamps. HID lamps contain compact arc tubes, which enclose various gases and metal salts operating at relatively high pressures and temperatures.
(HPS) HIGH-PRESSURE SODIUM LAMP - High-pressure sodium lamps operate by igniting sodium, mercury and xenon gases within a sealed ceramic arc tube. Sodium lamps emit light energy in the yellow/red/orange regions of the spectrum; the red spectrum stimulates flowering and fruit production. Many indoor gardeners switch to sodium lamps when it is time to induce flowering or fruiting of their plants.
HOOD - The reflective cover used in conjunction with a HID lamp. The more reflectivity a hood can provide, the more effective it is.
HOR - An industry code indicating that the bulb is to be operated in a horizontal position.
HOT SPOT (in this case relative to bulb and not reflective material) - The area immediately under an HID lamp where the light intensity is strongest, hot spots cause uneven growth, but can be remedied by using light movers or air-cooling the encased hood.
HOT START TIME - The length of time required to bring an HID lamp to 90% light output after a short power interruption.
IGNITOR - A component of the ballast necessary for the starting of the bulb in sodium systems.
INCANDESCENT LAMP - A light source which generates light utilizing a thin filament wire (usually of tungsten) heated to white heat by an electric current passing through it. Incandescent lamps are the most familiar type of light source, with countless application in homes, stores and other commercial settings. Light is produced by passing electric current through a thin wire filament, usually a tungsten. Incandescent lamps are totally ineffective as grow lights; they have very limited spectrum, are very inefficient in their conversion of electrical power to light output they also put off far too much heat per watt to use in horticulture, even if the above-mentioned problems did not exist.
INTENSITY - A term referring to the magnitude of light energy per unit; light intensity diminishes evenly as you get further from the source.
KELVIN TEMPERATURE (K) - The unit of measurement to express the colour (spectrum) of light emitted by a lamp; the absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source. A standard clear metal halide HID lamp has an average Kelvin temperature rating of 4,000K.
KILOWATT (kW) - A unit of electric power usage equal to 1,000 watts.
KILOWATT HOUR (kWh) - A measurement of electric energy. A kilowatt hour is equal to 1,000 watts of power used over a period of one hour.
LAMP - An electrically energized source of light, commonly called a bulb or tube.
LAMP LIFE - A measure of lamp performance, as measured in median hours of burning time under ANSI test conditions.
LAMP DEPRECIATION (LD) - The decrease over time of lamp output, caused by bulb wall blackening, phosphor exhaustion, filament depreciation, and other factors.
LAMP STARTING - Generic term used to describe a discharge lamp's starting characteristics in terms of time to come to full output, flicker, etc.
LIGHT MOVER - A motorized device which moves an HID lamp back and forth across the ceiling of a grow room to provide more even distribution of the light and reduce hotspots.
LUMEN - A measurement of light output; relative to human perception which refers to the amount of light emitted by one candle that falls on one square foot of surface located at a distance of one foot from the candle.
LUMINA IRE - A complete lighting unit, consisting of a lamp or lamps together with the components required to distribute the light, position the lamps, and connect the lamps to a power supply. Often referred to as a "fixture."
(MH) METAL HALIDE LAMP - A high-intensity-discharge lamp in which the light is produced by arcing electricity through a mixture of metal halides. The light produced by metal halide lamps is in the white-blue spectrum, which encourages vegetative growth and "bushiness" while discouraging upward growth. This is the bulb to use in the first, vegetative phase of plant growth.
(MV) MERCURY VAPOUR LAMPS - The oldest member of the HID family, mercury vapour lamps work by arcing electricity through mercury vapour. While more efficient than incandescent, halogen and fluorescent lamps, mercury vapour lamps are the least effective of the entire HID family. This, combined with an improper colour spectrum for horticultural applications, makes mercury vapour lamps a poor choice for a grow light.
MOG - Mogul base.
MOL - Maximum overall length of a lamp, from the tip of the base to the top of the bulb.
NECK - The narrow, tubular end of the HID bulb, attached to the threads.
PARABOLIC REFLECTOR - A lighting distribution control device that is designed to redirect the light from an HID lamp in a specific direction. In most applications, the parabolic device directs light down and away from the direct glare zone.
PHOTOPERIOD - The relative periods of light and dark periods within a 24-period. Also referred to as day length.
PHOTOSYNTHESIS - The growth process by which plants build chemical compounds (carbohydrates) from light energy, water and CO2 (carbon dioxide).
PHOTOTROPISM - The gravitation of a plant part toward a light source.
REFLECTOR - The term sometimes used to refer to the reflective hood of an HID lamp.
REFLECTIVITY - The measure of the reflective quality of a surface; the relative ability of a given surface to reflect light away from it without absorbing, diffusing or otherwise compromising the light’s quality, intensity and spectrum.
SOCKET - The threaded, wired receptacle that an HID bulb screws into.
SON-AGRO - A sodium bulb which, according to the manufacturer, produces 30% more blue light than standard sodium bulbs. The 430-watt SON AGRO also emits 6% more light than the standard 400-watt sodium lamp.
SPECULA REFLECTION - The redirection of incident light without diffusion at an angle that is equal to and in the same plane as the angle of incidence. The secular inserts included in Hydrofarm’s HID lighting systems work on this principle.
TRANSFORMER - The component in the ballast that transforms electric current from one voltage to another.
U (for UNIVERSAL) - An industry code indicating that the bulb can be operated in any position: horizontal, vertical (base up) or any other.
ULTRAVIOLET (UV) LIGHT - Light with very short wavelengths, out of the visible spectrum.
WATT (W) - A unit used to measure electric power. One watt equals one joule/second.

What are light cycles and how do I use them?

The amount of time your garden should be exposed to lighting depends on what 'cycle' your garden is in:
The 'Vegetative Cycle' of your garden starts with the sprout of the seedlings and can be continued indefinitely. In the veg cycle your garden will require a minimum of 16-18 hours of light and 6-8 hours of darkness daily. Since a given amount of light can only do so much, equal production can be realized in a smaller space with less plants, where the light is concentrated and the plants can grow more efficiently. Using more light helps additional co2 uptake.
Since a plant can be kept in the 'Veg cycle' indefinately, many growers cultivate 'Mother' plants. This plant is used for clone starts and never produces buds, only new growth.
The 'Flower Cycle' or 'Bud cycle' is typically equal amounts of light and dark, 12 hours on, 12 hours off or 12/12. This produces a change in the plants metabolism simulating Fall, shorter days....less light.
This is the cycle that the plants will show their sex. Usually, you'll be able to determine the sex within the first 2 weeks of 12/12. By the 3rd week most plants have developed healthy bud sites or pollen sacks. The plants will continue on the 12/12 cycle until harvest.
When someone 'Re-vegges' a plant that has been in the flower cycle, they're switching the light cycle back to 18/6 to stimulate new vegetative growth.

PAR for plants

While the lumens measurement is based on the sensitivity of the human eye to light, PAR Watts objectively measure the total watts of Photosynthetically Active Radiation (PAR) emitted by the lamp. It accounts for the nutritional value and is a direct measure of light energy available for all-important plant photosynthesis.

Should I use a light mover?
Light movers are mechanical devices that, as the name implies, move an HID in a fixed pattern over a garden. A light mover can increase the coverage of a light by 140%. The real advantage is MUCH more light is available to the plants when the light is in motion. With a stationary light all that is shaded will remain in the shade, but with a mover the light will hit from different angles giving better coverage.
Light movers are found in 2 configurations: spinning arms (kind of like a ceiling fan) and along a rail that moves back and forth. The rail version seems to be much more popular with Overgrowers, probably because it will accommodate an air cooled fixture.
Light rails come in a variety of lengths, but most can be cut to fit any application. Most growers prefer a "smart rail", that is, one that pauses at each end of the rail for a period.
The biggest problem with air cooling a light on a mover seems to be dealing with air duct slack. Apparently, if the light is close to the tops of the plants, the duct may be dragged through the plants, thereby damaging them. Overgrow poster Ferret devised a solution: Use a curtain track, not a rod but the track that has all the little hangers inside that slides very easily. I screwed this to the ceiling of room and used light weight string to attach the air pipe to the little hangers in the track. As the light moved the track hangers moved along with the air pipe stopping the air ducting from dragging over your plant tops doing damage.
The track cost about $15-$20 at any hardware or store. Simple to set up and it works .

Can blacklights be used for growing?
They can not.
Blacklights do not produce the correct spectrum of light to grow plants.
The only lights that currently produce the required color spectrum of light to grow plants are the following;
Suitable for Growing:

 Flourescent (Tube shaped)
 Compact Fluorescent (a flourescent tube with ballast included that screws into regular light fixture)
 Metal Halide (MH) Best for Vegetative growth, but it doesn't contain all of the spectrum needed later during flowering for truly outstanding buds. the light shines a blueish/white color
 High Pressure Sodium (HPS) Best for Flowering. Ok for Vegetative. shines a yellow/orange color. All can be purchased at your local home/lumber store.
Not suitable for growing:

 Blacklight type flourescent lights.
 ANY incandescent lamp
(if it screws into a regular lamp, it won't produce worthwhile buds). Exception, compact flouro mentioned above)
 Halogen
 Mercury Vapor

How do I manipulate the photoperiod for larger yields?

[DISCLAIMER]: This information is provided as experimental data and not fact.

The only photoperiod manipulation from years of experiments that offered discernible improvements was the following photoperiod adjustment made for 1 or 2 calendar weeks at the point of maximum flowering rate: Daylength of 21 hours, 36 minutes with a dark period of 12 hours. To accomplish this, you need a 7 day, 24 hour digital timer. During a 7 day calendar week on Earth, the "sun" only cycles 5 times. This permits easily switching back to the regular 12/12 at your discretion. You may want to only alter during peak flower production to stimulate the plant's metabolism. Using this photoperiod throughout the flowering cycle will cause this:
A variety that takes 49 days of 12/12 to mature, won't see 49 - 12 hour dark periods under 21:36/12 until almost 10 calendar weeks have passed.
The total increase in light energy is almost 80%, which will produce larger yields, if all of your other enviromental conditions are kept optimal.
The total increase in flowering period is only 40%, half the potential room for improvement. This means you don't have to be perfect to win out.
Selective application of the 21:36/12 photperiod for only 1 or 2 weeks extends the wait only 2 to 4 Earth days, which makes up the missing 2 complete day and night cycles each week on Planet Ito. This permits the additional light energy to be provided without purchasing additional equipment or overloading existing circuits, which maximizes the existing system's capabilities. The main advantage is that matched with co2 and optimal nutrition, the plants metabolism will increase dramatically. I have only successfully tested this photoperiod for two weeks. The potential for a net increase of 40% over the entire cycle (80% increase in light energy vs. 40% longer wait) is worthwhile. Don't be afraid!
Day 1 - Sunday, 6:00am til Monday, 3:36am
Day 2 - Monday, 3:36pm til Tuesday, 1:12pm
Day 3 - Wednesday, 1:12am til Wednesday, 10:48pm
Day 4 - Thursday, 10:48am til Friday 8:24am
Day 5 - Friday, 8:24pm til Saturday 6:00pm

Metal Halide safety and fixture recommendations.

HPS (High Pressure Sodium) lamps can burn in any orientation.
MH (Metal Halide) lamps come in three basic types:
 Base up (BU), which must be operated in the base up position.
 Horizontal (HOR), must be operated in the horizontal position.
 Universal (U), which may be operated in any position.
Orienting metal halide lamps in burning positions other than those specified can result in severe reductions in performance and potential nonpassive failure. Lamp life,light output and color can be affected by the burningposition. Some burning positions may need enclosed fixtures for safety reasons.
When replacing ANY HID (High intensity Discharge) lamp, never touch the bulb with bare hands. HID lighting gets exceptionally hot and any oils from your skin left on the bulb will burn and can cause the lamp to burst.
Always use soft, clean gloves when handling the lamps.
Observe extreme caution while foliar feeding any plants around exposed lamps. I suggest turning off any fans and ventilation while spraying the plants, any water blown onto an exposed, burning lamp can cause it to explode in your face. Be safe.

How to read light level with an SLR camera?

How to read light level with an SLR camera?
Using your SLR camera in manual mode, you can measure light level:
 Set camera ASA speed to 200.

 Set camera shutter speed to 1/125.

 Hold a large, white card (or sheet of paper) in the proposed plant location so that it gets max illumination.
 Be sure that nothing but the white card is showing in the viewfinder.

 Adjust f-stop on camera (or lens) until camera meter reads "correct exposure"

f4 = 64 foot-candles
f5.6 = 125 foot-candles
f8 = 250 foot-candles
f11 = 500
f16 = 1000
f22 = 2000
f32 = 4000

I use this technique to:
 Determine "hot" spots in the room - I put my youngest plants there.
 Determine "weak" spots - install reflectors as needed to bring up light levels.
 Determine when bulbs are getting weak - instead of "it looks dimmer than before".

What distance should my light be from my plants?
For (artificial) light, there is a law that always applies known as the Inverse Square Law. It states that light diminishes exponentially in energy as the distance is increased from the source.
A good example is that you might be getting 1000 PAR Watts at 4" from your light source, but that would change to 250 PAR Watts at double the distance (8"). This law makes it EXTREMELY important for indoor plant growers to get their light source as close as possible to their plants. The amount of light your plant receives is directly related to it's yield/flower density.
The problem: Indoor lamps used for plant cultivation (HID - High Intensity Discharge) give off large amounts of heat, to such a degree that they could cause damage to the plant if put too close.
Indoors, there is an optimum distance/height between the plants and the light source. This distance fully illuminates the whole canopy with direct light from the source, but is as close as possible to the plants for maximum lumen intensity. This will be called the OLH, for Optimum Lamp Height.
Ultimately, to get the best light efficiency from your lamp, you want it at the OLH at all costs. But how can you get it there without causing harm to your plants with the abundant heat?
First, try moving your light to the OLH and see what it does to your plants. If they have no problem, then you're fine. If you have a high output HID, this probably won't be enough.
Next, try actively exhausting your light hood by hooking up a direct exhaust system to the hood, and then move your lamp to the OLH and see if the plants are O.K. If the plants still seemed affected by the heat, then you must add glass to your actively exhausted lamp hood. Glass will absorb/reflect/filter some of the light energy being emitted by the lamp.

Nov 28, 2007
And the cardinal rule of grow rooms and electricity... IF YOU AREN'T 110% COMFORTABLE DOING THE JOB YOURSELF HIRE AN ELECTRICIAN!!! Especially in CA. Not worth it.