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What do the terms lumens, PAR, kelvin etc mean? Do you have some basic background to lighting terms?
(Contributed By Sureshot)

SO WHAT'S UP WITH THE SUN THEN?

When setting up an indoor grow two of the most important elements are quality and quantity of useable light that the plants receive.

Plants have the rare ability to manufacture their own food, this process is called photosynthesis. The main substance in this production, chlorophyll, uses light energy to convert carbon dioxide from the air and water and nutrients 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, namely the intensity, colour and duration of the daily light the plant receives.

Plants mostly use the same light spectrum as we do in that they too primarily are affected by the VISIBLE spectrum of light (there are theories surrounding the part UV plays in growth but more on that later).

The Visible Spectrum of light can be seen below...measured in "nanometres". The next image shows the same spectrum but measured in Kelvin?s and marked with common light sources and the spectrum they produce. Although plants react in some way to all forms of visible lights certain parts of the spectrum have the most efficient and important roles.

As you can see from the above diagram, chlorophyll activity is at it's greatest in the blue and red parts of the spectrum (5,500 Kelvin to 6,500 Kelvin and around 2,500 Kelvin respectively).

Cool (blue) light is most pronounced during the summer months when the sun is highest in the sky. It is responsible for vegetative growth. Warm (red) light, such as when the sun is lower in the sky during the fall harvest months, is responsible for triggering reproduction in cannabis in the form of male or/and female flowers.

Bringing your grow indoors allows the grower to control these factors, these seasons if you like. Indoor gardeners must attempt to mimic these natural tones, summer and encroaching winter, blue and red, to maximise their gardens potential. This can be done in two ways, control of the plants lighting schedule AND the correct choice of light source.

Terminology

Watts - This is a measure of the POWER needed to produce the light and is NOT in anyway a measure of the actual light, obviously though it serves as a good rough guide.
Lumen - "The unit of luminous flux in the International System" {Source : OG Glossary}. This is a measure of the actual light produced by the lamp. This is also the measure (along with Watts) you will hear most in lighting issues, it is not technically a measure of the light useable by the plant to photosynthesise (PAR - see below), but as it is assumed that the grower is using a light with an appropriate spectrum PAR is not often useful on a general level.
Photosynthetically Active Radiation (PAR Watts) - A measure of the light energy available to the plant for photosynthesis (i.e. the amount of light in the correct spectrum) that the lamp produces.
Kelvin - A measure of the colour spectrum of the light.

What is a horticultural lighting system made up of? What is a contact relay?
(Contributed By Sureshot)

PUTTING THE SUN IN A WARDROBE

Light Innards

All the bulbs discussed above are made up of both a bulb (or tube) and a ballast. The ballast effectively steps up domestic power in order to power the demands of your lights without burning anything down, they basically consist of a transformer, capacitor and in some cases an ignitor (see the electrical issues section of the FAQ for more information regarding the internal make up of a ballast).

Horticultural ballasts tend to be "remote" from the lamp and encased in a vented case for safety. In Fluorescent tubes this ballast is usually found in the fixture (Compact Fluorescents are a different matter, as these are primarily used in domestic light sockets the ballasts have to be built into the bulb itself).

This is similar in many low W HPS and MH lights. It is however desirable to have the ability to separate bulb and ballast for heat reasons and this "remote" ballast layout is usually the preferred one for HID grow light setups :

This layout is used to enable the grower to remove the ballast from the direct growing space (or at least to a better position e.g. high or cooled) as it is another source of heat apart from the bulb.

Ballasts run HOT! Hot enough in some cases to give a nasty burn. DO NOT handle a ballast that is running (unless you got ya oven gloves on!!). When running high wattage HID lighting with a timer you will also need a contact relay, this has two plugs, one of which plugs in through the timer and the other straight to a socket, the timer therefore only has to turn on the contact relay (rather than a fucking great big ballast) which in turn starts up the ballast.

If you keep getting home to your lights on (or off) when they shouldn't be, buy one. This one cost less than £30 (or two decent timers, lol). You can also get timers with these relays built in for conveniance. Notice the different gauge of the wires going to timer and full draw.


How much light do I need?
(Contributed By Sureshot)

By Lumens

Indoors, 2000 lumens (about 20W) per sq. ft. is about as low as you can go indoors. Under this mark, plant growth will slow, and internode/stem length will increase as the plants s t r e t c h for the light. More adjusting, more work, grr.

I tend to think that an optimum level is about 3,500 - 5,000 lumens per square foot of grow space. This means that a 400W HPS pitching out 50,000 lumens will cover about 10 foot square optimally (@ 5,000 lumen per square foot). This is the equivalent of around 40 Watts per square foot.

You often hear 30 - 50 w per square foot touted as a rough rule of thumb, I think it's most however efficient to be at the lower end of this and could point to grower after grower who get great results from this amount of light, though could equally point to those who would go to the upper end of this as their optimum. Not all is simple already you'll note!

For note though, I run my flowering at 35w per square foot unless it's a particularly high demand Sativa. As a further note, there is a general tendency amongst growers that there is "no such thing as too much light". This is bullshit. Go over the top and regardless of whether you have your heat under control you will bleach your plants.

By Growing Space

As lighting intensity drops as you move further from the bulb any lamp has a limited maximum distance from the plant. After this distance growth will be below optimum. An approximate guide would be:

• 250 watt - 2' x 2'
• 400 watt - 3' x 3'
• 600 watt - 3.5' x 3.5'
• 1000 watt - 4' x 4'

This of course assumes a square shaped grow space. If you are working with different shaped rooms, say for example a rectangle, it may be worth working with a combination of lamps. For example a 2 foot by 4.5 foot room may be better lit by 2 x 250w rather than a single 400w.

What light should I use?
(Contributed By Sureshot)

LET THERE BE LIGHT

There are basically three commonly accepted types of lights that can be used to grow marijuana (beyond the sun of course but then i did say INDOOR growing).

1. Fluorescent Tubes & Compact Fluorescents (CF) (commonly known as energy saving bulbs);
2. Metal Halide (MH) - High Intensity Discharge (HID) lamp;
3. High Pressure Sodium (HPS) - High Intensity Discharge (HID) lamp.

Before discussing the advantages and disadvantages of these lights it's worth examining the genmeral terminology of lighting. Check the Lighting Basics question for this.

Fluorescents

Fluorescent tubes and CF bulbs are incredibly useful and cheap lights that can be used to good effect both in the seedling stage and vegetative stage of plant growth. They work by passing an electric current through a mixture of gases in order to make them glow, this glow is the light. Be sure to select a tube with a useful K (Kelvin) rating (see above) and these lights can be used very effectively; there are however some fairly straightforward drawbacks to the light they produce.

1. The lumens per watt rating of a fluorescent light is rarely a touch on the equivalent MH/HPS. 40w of flo light is around 3000 lumens, or 30,000 lumens per 400W, now your average MH 400W will produce 36,000 lumens and an HPS 45,000 lumens.
2. The lights intensity is substantially less than MH/HPS and penetrates less distance into the canopy. For this reason Fluoro's are best kept as close to the growing tips of your plants as possible, this has its own problem... more adjusting! There are though arguments FOR the use of flo's in certain situations.

Fluorescent tubes and CF's (which are a little hotter but not much) run comparatively cool against MH/HPS meaning that they can be utilised in situations where space is tight and/or ventilation is poor. The disadvantages must still be kept in mind and plants grown under fluoro's should be kept low (to make up for low light intensity) unless there is substantial side lighting as an addition to the main top lighting. The ability to side light is indeed a further advantage to fluoro use.

Flo's are also extremely useful for cloning and seedlings. MH/HPS can be too intense for these early stages of growth as the plants cannot absorb water fast enough (developing root system) to equalise the amount being lost through transpiration through the plants foliage (or at least that's my way - if you do use MH/HPS for your seeders/clones keep the lights a decent decent away particularly for clones).

Most people however seem to argue for using flo's on a cost basis, these people, in my humble opinion are misinformed and/or short sighted....

So yeah, flo's... Passable but limited. Available everywhere and locally, cheap up front, good for clones and seeders and available in a wide range of spectrums.

Your vegetative growth will be fine unless the flo's are too far away (or of too little intensity) in which case the plant will stretch but during flowering buds tend to be a little airy. The initial stretch phase of flowering can be a real pig as you will be moving the lights so often to match the pace of the s t r e t c h.

High Intensity Discharge (HID) Lamps

The most commonly (and best) used lamps in this category are MH and HPS lamps, these individual lamps have best use purposes but HID lights in general have several advantages (and indeed disadvantages) over fluorescent lamps and tubes.

HID lighting is generally accepted as a better light for growing cannabis for a several reasons:

• Deeper penetration (oo err ladies);
• Higher lumen rating per watt;
• Better suited light spectrums.

It does however pose problems, namely a higher temperature and hence the requirement for MUCH more substantial ventilation.

Metal Halide (MH)


MH lamps are largely recognized for their performance during vegetative growth, they produce a light in the blue spectrum which is known to be influential in stem and leaf growth. They work by passing an electrical current into a tube inside of them which is made of quartz and further enclosed in a glass layer, inside the quartz tube is a mixture of mercury, argon, and various (guess what) metal halides (for example sodium iodide). The charge passed through this induces both a visible light and an invisible (UV) one.

(Useable) Lamps come in ranges from 100 to 1,000W and produce between 9,000 to over 120,000 lumens of light. This light is largely around the 4,000 Kelvin mark but if you shop around you can buy bulbs with a more efficient rating around 5,000K.

Because of this "blue" light range MH lamps are best used during vegetative growth, they can however be effective in flowering too though not as effective as HPS. HOWEVER, due to the added invisible light from the UV produced resin production MAY be greater under an MH lamp, this is UNPROVEN however. More on MH Vs HPS below.

High Pressure Sodium (HPS)


The HPS lamp is often regarded as the best all round lamp to have. Not as effective as the MH in vegetative growth, more effective in flowering and generally a higher par and lumen output per W than MH. HPS lamps work in a similar way to MH lamps except the inner tube is ceramic rather than quartz (withstands higher temperature) and this tube is filled with Sodium, Mercury and sealed with Xenon gas.

HPS lamps come in ranges from 70 to 1,000W and produce upto 145,000 lumens. They produce light in a redder spectrum (2,200K) that is very efficient for flowering. These lamps do not emit any UV light.

Some newer HPS (son Agro) have an extra coil to produce a small amount of blue light these bulbs are available in 250, 400 and 100W and, for example, the 400W bulb would be 430W, these bulbs can be used in a standard HPS lamp holder and ballast. This allows HPS users to reap the benefits of MH (tighter internodal space, stronger stems etc.) without giving up the benefits of HPS.

HPS Vs MH

The HPS Vs MH argument continually rages. It is clear that MH has added benefits in vegetative growth and HPS has added benefits in flowering, what is unclear however is how these benefits weigh up in choosing an overall lamp, I would say that given the option to exclusively use one lamp for the entire cycle I would go for the HPS and use HPS son agro bulbs mostly due to them being generally more efficient lumen wise than MH.

Note : You must remember that HPS and MH bulbs use different ballasts, you cannot plug an HPS into MH ballast or vice versa, or at least not without spectacular effects!

DO NOT USE......

• Incandescent (normal household) bulbs - they produce too little useable light and emit too much heat in doing so.
• Halogen bulbs - Again, too little useable light, too much heat.
• Mercury Vapour bulbs - Now MV bulbs have a larger amount of useable light but like incandescent and Halogen they emit far too much heat for each lumen of useable light.
• Candles - *laughs*
• Blacklights - Wrong spectrum, no power, everything you heard at the pub IS WRONG. *chuckles*

Heat and ventilation

HID lighting rigs (lamp AND ballast) produce quite a lot of heat whilst running. If you touch a warmed up HID lamp with your bare hands you will burn immediately, even remote ballasts are difficult to handle with bare hands when they have a load going through them.

The heat from the lamps can be combated using a variety of cooled hoods which can be bought or made (search OG for ghetto heat dispersal).

Ghetto Hood:

• Ghetto Hood
• Ghetto Hood 2
• REALLY Ghetto Hood
• Build Your Own Cool Tube
• Some examples (bottom of page) of some More Ghetto Hoods

It is advisable to have thought about ventilation (intake, exhaust and circulation) before planning your grow and buying your light. There is no point having a flash 1000W lamp that burns all your plants.

Hanging Your Lights

Your lights are going to need adjustment fairly often as the plants grow. Most people use a simple chain system but I find it to be a pain and very messy and so invested in a set of the below, they work fantastically well. Working much like seat belt rollers they allow you to set a height, tighten a wingnut and from then on your lights will only travel up, just push them up and the cable is all stored on the roller, fucking great, no more struggling with chains ever again.

Safety

Safety is everything, don't let your grow kill ya! Fire and smoke alarms should be installed near the entrance to your grow and all care should be taken with all the water used in your garden. Mount ballasts off the floor. Run your room for a few days/weeks supervised before leaving it for too long.

Safety Readme

Lamp Ratings

So glad I didn't have to compile this:

Lamp Rating Information

Can I grow with blacklights?
(Contributed By MacGyver(BB))

Black lights are just a fluoro tube with a coating on them. The coating filters out all but UV light. Basicly you'd be better off using a normal fluoro, so you get the whole spectrum, instead of just a small part of it.

There are actual UV bulbs, but they are meant more for air purification. Some speculation has also been done as to the usefulness in UV in the stimulation of trichome development.

Should I add side lighting?
(Contributed By flyboyscott68)

Adding fluorescent side lighting is definately useful in your grow. This side lighting, though low intensity, will allow lower budsites to develop. The low intensity and low heat also allows the grower to get this side lighting right in amongst the foliage.

What is a flip flop relay?
(Contributed By MacGyver)

Well I've posted about this before, but I thought i'd bring it up again seeing that this forum has exploded in popularity since SS became a mod (good show man).

Flip flop works on the principle that in flowering, your lamps are on a 12/12 cycle. It's a good money saving idea, and reduces th number of independant circuits needed by half. This also reduces the possibility of blowing breakers when lamps come on.

A flip flop timer can be purchased as an assembled unit (which is what I use) or as a component that attatches to a standard timer. It is like the contact relay that SS mentioned in the Light FAQ, only it is called a double-throw relay or timer. This means instead of turning the power on or off, poweris diverted from one bulb to another every 12 hours. This relay goes between the ballast and the bulbs, instead of between the outlet and the ballast. The ballast itself runs 24 hours a day.

This means two lamps can be run off one ballast and one timer, the only disadvantage is youll need two seperate light-tight bud chambers.


How can I make best use of my light? What is a good reflector for the walls of my grow room?

• What is Mylar and how can I use it?
  Mylar® is a biaxially oriented, thermoplastic film made from ethylene glycol and dimethyl terephthalate (DMT). OK now that I have your attention. Mylar is a trademarked name owned by DuPont and covers a LOT of territory. The Mylar we are interested in is Metallized Polyester film. First, a safety note - Mylar is flammable, it reacts quickly to direct heat!
  
  The reflectivity of Mylar is 97% - 99% (according to the manufacturer) which is excellent. It also reflects much of the infrared spectrum. Mylar comes in a multitude of sizes from small squares to fairly large rolls, so it shouldn't be too hard to fill your reflectivity needs. There are different material thickness also, with the main ones being 1 and 2 mil (.001? and .002?) at most hydro shops..
  
  The extra money for the thicker Mylar will be offset by the extra durability and installing ease. Two-sided tape makes installing Mylar a lot easier. An alternative is to use squares of duct tape stuck to the Mylar, and staple through both to the wall behind.
  
  Mylar polyester sheet and film is inert to water and acts as a moisture barrier as well as being unaffected by oils, greases and most aromatics. It can be cleaned with Windex, alcohol or any other mild household cleaner
  .
• Can I use Aluminium Foil?
  Aluminum foil is no more than 55% reflective. If used, make sure that the dull side is the one that is used to reflect the light. When it becomes creased its reflectivity is even lower (around 35%.) It is also very dangerous to use because it is electrically conductive, and is a fire hazard when it is in close contact with HID lighting.
  
  Aluminum foil creates hotspots easily, and attaching this to walls is a pain and usually using aluminum tape or glue is the best way. This should only be used as a last resort, and even then its usefulness is questionable.
  
• Can I use mirrors for reflectivity?
  A mirror dosen't reflect light, just image. A mirror is basically reflective backed glass and the glass will absorb light (and also refract it), since the light travels through the glass 2 times it makes it even worse.

Can I make my own light reflector?

• CF Reflector - Homebuilt CF reflector
• $15 Reflector - Tick bends a cheap reflector
• Mailbox Reflector - Make your hood from a standard mailbox
• Octagonal Hood Plans - The Dutch swear by them
• Wood Built Hood - Covered obviously

Should I use a dimpled or polished reflector?
Dimpled V Polished - Self explanatory