Guide to lighting and bulb types.
Here is a guide to lighting and light bulbs and what they will do for your plants. (feel free to suggest any changes if you see an error ) I didn't write it all.....just compiled it and added a bunch.
Indoors, 2000 lumens per sq. ft. is about as low as you want to go indoors. If you get under this mark, plant growth will definately not go as fast as possible, and internode/stem length will increase. Also, light distance to plants will be much more critical. Daily adjustments to the lamps will be necessary, meaning you get no vacations. 2500 lumens psf should be a good target, and 3000 is optimal if your going to inject or enrich CO2 levels.
High Pressure Sodium - or HPS lamps emit a pink or amber light. They are used generally for lighting parking lots and other areas where the color of the light is not all that important. HPS lights are much more efficient than MH ones, producing more light and less 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. There is a relatively new type of HPS lamp that has become available. It is called the...
Son Agro lamp
Basically the designers of this special lamp took a 400w HPS lamp, and added another 30W element to it, However, this new element puts out blue light, to help fill in the parts of the spectrum that a standard HPS light is missing.
Metal Halide - Metal halide (MH) lamps can be used for vegging and flowering (but primarily vegging), but there are two problems that they have when compared with high-pressure sodium (HPS) lamps. The first is that they don't emit as much total light. HPS lamps emit more than 20% more light, so MH lamps are not as intense when covering the same area. Second, they do not emit as much orange and red light as HPS lamps. These spectrums seem to promote flowering.
However, MH lamps do have several advantages over HPS. First, they are less expensive to purchase. Second, the light does not have a really weird telltale spectrum. It looks white, not pink or amber/orange.
Third, the lamps emit more UVB light than HPS lamps, although still in very small amounts. The amount of UVB light plants receive is directly related to the quality of the harvested buds. The more UVB, the higher the quality.
Buds grown under MH light will not be as big as buds grown using HPS lighting. However their quality will be as good or better.
Compact Flourescent - Or CFL . This type of light is perfect for seedlings, cuttings, and clones. They can be used for vegging and flowering but are not as effective as high intensity discharge lights like the HPS. Fluorescent lights are low intensity and need to be placed quite close (2-3 inches) to be very effective. They are a poor light source for flowering and budding primarily because of their low lumen output.
One advantage of CFLs is that they produce very little heat enabeling them to be kept quite close to the plants. But even with cool bulbs, always remember a fan for circulation. CFLs come in both warm and cool spectrums. A mix of both is ideal but warm is generally for flowering and cool for vegging. They are excellent for side lighting and can be found relatively cheap and many grocery stores and the like.
Flourescent Tubes - Fluorescent tubes have been used to cultivate and flower marijuana. However, buds grown under these lights are usually fairly small and loose. The reason for this is that the intensity of the light, that is the amount of light that is produced by these lamps, is relatively low. In addition, the light is produced over a large area. The result is a lower amount of light spread out over a large area, so the amount reaching the plants is a small fraction of the amount the plants receive from a metal halide (MH) or high pressure sodium (HPS) lamp (and even Compact varieties)
Fluorescent tubes are more expensive than HPS lamps, too. The initial cost of a fluorescent is less than a HPS. However, when the cost of light is considered the cost picture changes. HPS lamps emit 2 1/2 to 3 times the amount of light per unit of energy consumed. The efficient HPS lamp is much cheaper over its life than a fluorescent tube.
Although you can grow marijuana using a fluorescent, you will produce a much higher yield of better grade grass cheaper and easier using an HPS lamp than a fluorescent.
Incandescents - Not generally used in Marijuana growing. The common incandescent light bulb emits some of the frequencies of light the plant can use, but it also emits a high percentage of far red and infra-red light which cause the plant to concentrate its growth on the stem. This results in the plant stretching toward the light bulb until it becomes so tall and spindly that it just weakly topples over.
There are several brands of bulb type. One is the incandescent plant spot light which emits higher amounts of red and blue light than the common house light bulb. It is an improvement, but has it's drawbacks. Tbe bulb is hot, for example, and cannot be placed close to the plants.
Consequently, the plant has to stretch upwards again and is in danger of becoming too stretched and falling over. The red bands of light seem to encourage stem growth which is not desirable in growing marijuana. The idea is to encourage foliage growth for obvious reasons.
Mercury Vapor - Not generally used for marijuana growing. Mercury Vapor lamps are less efficient than the fluorescent (FL), and can not be positioned as close to the plants, so the plants will not be able to use as much of the MV light. The light distribution is not as good either. MV lamps simply are not suitable for indoor marijuana gardening. Use flourecent, MH, or HPS lamps only.
Halogen - Not generally used for marijuana growing. High pressure sodium (HPS) lamps emit at least seven times more light than halogen lamps. A garden growing under a 1000-watt HPS lamp is expected to yield one pound or more than one under a 1000-watt Halogen.
The initial cost of the halogen bulb is much cheaper than an HPS lamp. However, when the cost of generating light is considered, HPS lamps are much cheaper. For every dollar you spend on electricity for lighting using a halogen bulb, you pay only 14 cents or less using an HPS lamp.
In addition to the cost of electricity, consider the space being used and most importantly your time. You expend essentially the same effort to produce 100 grams rather than 400-500 grams. That alone makes a small harvest considerably more expensive than a large one.
Last edited by Cannagirl; 07-01-2007 at 01:22 PM.
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Lighting update so generously penned by SirStynkalot
Lighting update so generously penned by SirStynkalot. Much thanks SirStynk It's through member contribution that GK knowledge grows.
If any members have additions of their own send them to Admin PM and we'll get them inserted.
1. The best way to assess light available to plants per square foot is by taking a PAR reading, which requires specialized equipment. Cannabis plants absorb light on a bimodal curve with very steep peaks in in specific nanometer ranges - I believe around 430 nm and around 670-680 nm. Official PAR measurements cover a range rather than the peaks, meaning that even PAR readings are inaccurate when measuring light efficiency.
I mention this because a lot of LED companies are capitalizing in this area, but their results vary significantly and there is no way to accurately assess their performance at any given luminosity. This is largely due to technology limits. There are huge difficulties involved in breaking down and stabilizing electrical currents at the low, low levels necessary to operate LED diodes. How the LED company designs the transformer has as much impact on plant uptake efficiency as diode selection does, but a background in electrical engineering is required to accurately assess different brands. I don't have such a background.
My best advice when considering LEDs in this market flooded with snake oil is to go by what your eyes tell you. Grow long enough to establish a baseline of your performance and understand what the upper ends of the craft can achieve, then observe another grower who's using LEDs, estimate where he/she is on the grower experience continuum relative to you, and judge their results to decide if you think you could make the same product with the same equipment and be happy with it. Best advice I can give.
2. Regarding HPS and Metal Halides:
There have been a few significant changes in the last five years.
There is a new HPS model on the market (currently only produced by Gavitas to my knowledge) that is a completely different style of light designed specifically for horticulture. The bulb has two sockets and emits an arc across the length of the bulb instead of in the middle, as far as I understand it. It comes with its own open reflector that is meant to be hung slightly higher and cast the light in a narrower footprint. So far, grower reports are that they're seeing increases over standard styles. The theory is based on reducing lumens lost by being cast outside the canopy and using slightly higher output technology.
Metal halides have evolved as well. Currently there are a number of differently colored Metal halides available. Many growers claim increased potency and faster flowering times (but lower yield) from warmer spectrum metal halides - generally in the 4000 Kelvin range. My knowledge in this area is sketchy, but the theory is that the warmer color spectrum is close enough to the required nanometer range for PS-I and PS-II pathway photosynthesis to work, and the increased output in blue, yellow, and UV ranges over HPS lights increase production of THC and some terpenoids.
It is worth noting here that ALL HID lights, and Metal Halides in particular are dangerous. Metal Halides should NEVER be used in an open fixture. Seriously. If you are working in the room and the bulb blows, you're blind for life. The risks common to both models are well documented in other locations. READ before you buy.
There are two types of flourescents most suitable for marijuana horticulture: T5HO fixtures (thin bulbed high output) and CFLs. Both have very specific proper uses.
T5HOs should only be used for vegetative growth. Only use bulbs with a 6500k color temperature (marketed as "daylight spectrum"). They must be kept roughly 2-8" above the plant canopy to avoid burning based on environmental factors, and they emit light in levels useful for P-I photosynthesis only about 18" under the bulb. That means they're useful for vegging plants until they're about 18" tall or maintaining mothers that aren't heavily cloned (as in, chopped in half twice a month).
100w replacement CFLs (26 actual watts) can be used to veg clones or very small plants. They burn at two inches and don't emit enough light for fast growth past about six. Larger wattage CFLs have better penetration and generate more heat, but I don't have much experience with them. 6500k spectrum bulbs should be used for veg, and 3000k bulbs (they might be 2800k, can't remember - marketed as "warm white") should be used for flowering. CFLs tend to add at least 10 days to the flowering cycle and develop lower weight watt-per-watt, but the quality is very high due to the much higher UV output. There is a lot of potential application for micro-growing, but if you have a space over about a 2'x2' cabinet it's probably more worthwhile to use HID lights of appropriate wattage for flowering.
Flourescents encourage tighter node spacing, smaller leaves, and slower overall growth and maturation relative to Metal Halides. They also cost significantly less, which is a large factor in choosing lights for an "unproductive" stage of plant growth. You make the call.
lighting guide topic 1
Submitted by Skunky. Pay attention folks, these guys know their shit.
To expand upon the PAR readings discussed in 1. True it is being abused. But let me expand.
PAR is essentially 400nm to 700nm. PAR readings take into account anything within that range. While it is known that Chlorophyll a and b predominately absorb and utilize light in a bi-modal fashion mainly around the 430 and 630nm range. That had been shown over the years to be a generalization to some extent. While those may be the predominately favored wavelengths it is not the end all be all.
There a papers that show how green light goes against the current dogma that green light is all reflected. Well not all of it evidently. In the presence of ample blue and red green provides deeper penetration. Though it's still all debatable at this point. Though there is some compelling evidence. However when choosing a Light for purchase and referring to par pay attention to the spectrum. If using LEDs pay attention to not only the spectrum but types of diodes. Not only by manufacturer but also by type. Even when it comes to top LED manufacturers certain LED types are more efficient than others.
Blue are the most efficient, followed by reds then the whites are gaining in the aspect. It's also a main topic of using most efficient blue leds with white phosphors to attempt to further improve white lighting. As an example with my RW-150. I can take PAR readings with the whites only and the reds only, even with spectral variation reducing LED by 10% if using quality driven properly it will be equivalent at around 45-60% the wattage in LED compared to that it would take for conventional HID such as MH and HPS.
However, CMH is a little different and from my experience with all 3 would be more like 60-75% of the same wattage required from LED. Even HID guys who are reluctant to try something like induction or LED will say CMH is a great light source with cooler temps than conventional HID. Regardless in reagards to quantification, photons are photons. If I have an HPS producing mostly in the orange range vs a LED with some cool whites that contain a little of everything, importantly the blues and greens, then extra reds to add the extra flower kick and the PAR reading for HPS is lower than the LED the LED no doubt has more flowering power per watt. I can measure with a quantum sensor using cool whites versus reds. They are about equal. That equates to saying that given the scenario above an LED that appears to have close to double the par output could have equal or slightly more than the HPS just solely in the spectrum range that encourages flowering, then you can add in the rest accounting for the blues and greens and everything in between.
Any one who believes HID is an efficient or the best light source hasn't looked at the data nor tested the waters for themselves. HID while they are tried and true and you can't go wrong, they are highly inefficient hence all the heat we've all battled over the years. More heat doesn't mean more power. Just like in engines it means more loss of power since it wasn't actually put to work it just radiated into the environment with no other benefits other than raising transpiration rates. In that sense that is now one of the greater benefits of HID. They are decent light sources and even better heaters. Heat helps regulate metabolism and growth, within a certain range. HID and LED make a great combo, though they are both more than capable on their own. As long as you don't buy junk that won't last you can't go wrong either way.
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