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Lighting ~A Cultural Healing and Life Compilation and Writing. Emoticons are safe bonus links, most youtube, click them. Advanced Section I - Understanding light, photosynthesis and how to select grow lighting Advanced Section II - Lighting & Reflector Section Advanced Section III - Plant Growth and Light Advanced Section IIII - Understanding Light Measurements Advanced Section IV - Advanced Lighting Information and formulas. Indoor Garden Environment Advanced Section II Lighting Technology & Reflector Section Click emoticons This section discusses lighting, ballast, reflector and light cooling options. Think you know about light and growing? Take the test and see if you should read the following or not. The "Lighting Dunning-Krueger Test" : This section's information is a compilation of lighting information and my writings as to help explain light and how to use that information as to create truly professional grow environments or just to advance ones understanding of light. Since most growers are not agriculturally trained their is often misunderstandings and half truths taken for facts. In part, this aspect is what prevents skilled plant growers from achieving advanced level crops in regards to gardeners who do not optimize their lighting for their plants and are working for optimized conditions. This document is an attempt to answer that flaw within the home gardener community. Growing optimum requires lighting knowledge (spectrum and how to use it with plant development), environment (temperature, humidity, air flow, in alignment with plant development) and plant nutrition in alignment with plant development and conditions. When these factors align they unlock the potential of your plants to what is possible for professional indoor gardening from enclosed growing rooms to greenhouses adding additional lighting to daylight. Below is a compilation and writing on various lighting options and how to use them. In this section I will discuss lighting options in an ethical and honest presentation as I understand it. Garden Lighting Options Metal Halide Lighting Metal halide lamps are widely used in the horticultural industry and are well-suited to supporting plants: Often used as secondary lighting in agriculture operations and not as a main light. Agriculture operations often use the sun as main light source with other lights acting in secondary or boosting/management aspect. Used in early plant developmental stages by promoting stronger roots, better resistance against disease and more compact growth. The blue spectrum of light encourages compact, leafy growth and may be better suited to growing vegetative plants with lots of foliage. A metal halide bulb produces 60-125 lumens/watt, depending on the wattage of the bulb They are now being made for digital ballasts in a pulse start version, which have higher electrical efficiency (up to 110 lumens per watt) and faster warmup.[14] One common example of a pulse start metal halide is the ceramic metal halide (CMH). Pulse start metal halide bulbs can come in any desired spectrum from cool white (7000 K) to warm white (3000 K) and even ultraviolet-heavy (10,000 K) Combination MH and HPS ("Dual arc") Combination HPS/MH lights combine a metal halide and a high-pressure sodium in the same bulb, providing both red and blue spectrums in a single HID lamp. The combination of blue metal halide light and red high-pressure sodium light is an attempt to provide a very wide spectrum within a single lamp. This allows for a single bulb solution throughout the entire life cycle of the plant, from vegetative growth through flowering. There are potential trade-offs for the convenience of a single bulb in terms of yield. There are however some qualitative benefits that come for the wider light spectrum. Metal Halide and High Pressure Sodium (HPS) explanation Light Emitting Ceramic Metal Halide Lights https://www.growweedeasy.com/cannabis-grow-lights#CMH-Ceramic-Metal-Halide What is an LEC grow light? "LEC" stands for "Light Emitting Ceramic," and is a name for a type of metal halide known as a "ceramic metal halide" or "CMH." It operates a lot like a regular metal halide except instead of using quartz it uses a ceramic arc tube, very similar to what's used in HPS grow lights. This gives ceramic metal halides some distinct advantages. Compared to regular MH bulbs, LEC lights give off a more natural color, produce more light per watt, and last longer. It's more common to see these called CMH grow lights, but LEC is starting to become a lot more popular, probably because it's reminiscent of "LED" grow lights which have been hailed as the grow light of the future, until now! When it comes to growing cannabis, what advantages do LEC grow lights have over traditional grow lights? Although this has yet to be verified with scientific testing, their has been much claim of higher quality harvest with this light technology. They produce a natural spectrum of light that looks just like the sun, making it really nice to look at your plants since they're in full color. Having natural light makes it easier to diagnose problems compared to other types of grow lights which can produce purple (LED) or yellow (HPS) light that makes it hard to accurately see how healthy your plant is. Photography is better under this light spectrum. Many LEC grow light models come with a built-in ballast which makes them "plug-and-play" (you plug the light directly into the wall) like an LED, as opposed to most HID grow lights which need a separate ballast LEC bulbs last longer and keep their brightness for longer than a standard Metal Halide What disadvantages do LEC grow lights have over traditional grow lights? Unfortunately, LEC grow lights generally get lower yields than HPS grow lights because they are less electrically efficient (produce less light for the same amount of electricity Hempyfan's input, LEC grow lights are ideally used the same as traditional metal halide lamps. This lamp may be a good consideration where you would also consider an LED light as a main light source and/or with consideration when adding additional lighting. Quick Reference for Grow Light Efficiency (how much light produced initially compared to electricity for the most common cannabis grow lights) CFLs - 50-70 lumens/watt Standard MH - 80-90 lumens/watt CMH / LEC - 90-105 lumens/watt HPS - 105-150 lumens/watt LED (unfortunately lumens aren't a good measure of LED brightness) Note: For most HID grow lights (MH, LEC, HPS), the most electrically efficient bulbs are around the 600W mark. Smaller and bigger bulbs are almost always less electrically efficient. For example, a 150W HPS bulb produces about 105 lumens/watt while a 600W HPS produces about 150 lumens/watt. Light Emitting Ceramic Metal Halide Lights, LEC metal Halide High Pressure Sodium Lights (HPS) HPS Lighting is the accepted standard for which most in the indoor hobbyist grower and cannabis industry will relate to. https://en.wikipedia.org/wiki/Sodium-vapor_lamp#High-pressure_sodium This is due the specific indoor requirements of cannabis growers to have the HPS light as the main light source of the grow. HPS Aspects: Established standard for main light indoor growing. Ballast Types - Click link below for a bigger write up. http://gardenculturemagazine.com/growing-environment/grow-lights/best-grow-light-ballasts-magnetic-vs-electronic Digital - https://en.wikipedia.org/wiki/Electrical_ballast Depending on company firmware, efficiency can be improved. Not generally compatible with metal halide bulbs but they do have bulbs for similar spectrum that can run on digital HPS ballast. Conversion bulbs. Dimmable Ballast Most ballast require you to use the rated type of bulb the ballast being used. For example, typically a 1000w dimmable electronic ballast will require a 1000k watt bulb regardless if set at 1000w, 600w, 400w, 200w depending on options. However, some electronic ballast can use the bulb for the wattage setting independent of the ballast rating but will not be able to increase beyond the light setting. Magnetic - ballast are considered older technology. Often used with metal halide and HPS bulbs. Heavy Generally are hotter and less efficient than digital ballast. Often require cooling. From air conditioning the grow area Air cooled hoods Combination of both. Can be set up for horizontal or vertical growing. Not all bulbs can be used for vertical growing Check bulb manufacturer before purchasing bulbs for vertical requirements. Bulbs can be obtained in various spectrum qualities. Bulbs have good (accepted indoor standard) penetration. Will vary from spec to spec/bulb to bulb. Bulb availability in a range of price ranges. Par is most useful measurement in my opinion. 800-1000 umol (par) is ideal range for indoor large plants. Bulbs are easy to obtain for standard sizes such as 400w, 600w, 1000w. Other bulb sizes may have local difficulty in obtaining and may require internet sales depending on your location. Bulbs deteriorate at a known rate. Some will change bulbs at 1/4 year, others at 1/2 year up to a year is most common. Budget people tend to go a year on average or more. Bottom of graph will give you the generic spectrum for various Deterioration % rates Adjustable ballast settings Review your bulb manufacture for specifics. General Bulb Deterioration rates Spectrum Ratings of Metal Halide (MH) and High Pressure Sodium (HPS) Click for information on selecting the correct bulb size for your grow. Below is a snippet of the article above. Video on light deteriation Union Break! Plasma Lighting High pressure sodium lamps are known as the most efficient lamps to produce photons for grow light. However, the quality of that light is not so good. Analysis of the HPS spectrum shows a start of the effective spectrum at about 560 nm (yellow to red). Below that wavelength there are a few small spikes, but not a balanced continuous availability and not enough in the blue spectrum. Research in greenhouses shows that you need at least 7% blue light (in a greenhouse from sunlight) for a healthy crop, as the blue light also maintains the photosynthetic system. It is important to know that in high intensity lighting there is not a lot of difference in efficiency between blue and red light. In climate rooms it is common to use Metal Halide (MH) lamps to add additional blue spectrum. MH lights however do not have a long lifetime, are generally not very color stable, have a spiky spectrum, are not as efficient as HPS and generate a lot of heat. Ceramic Metal Halides (CMH) are already better in stability and efficiency but still do not have the spectral quality of the plasma lamp nor the UV radiation. So how efficient is Plasma light compared to HPS? Is it an alternative? The plasma process of generating light is by itself very efficient: The conversion from energy into actual light is very efficient and generates a very low percentage of heat radiation in the light; the light itself is very “cool”. In the process of getting the energy to the small plasma cell you still lose a lot of energy, which is dissipated into convection heat from the fixture’s driver, power supply and emitter. That heat will never reach the plant though as it rises up and is extracted. For temperature controlled climate rooms there are air cooled LEP fixtures available as well. LEP is more efficient than high temperature MH lamps and much more stable. The lifetime is as much as 30,000-50,000 hours compared to the 2,000 to 4,000 of a MH. It has a better light quality and is more efficient than MH, but is it more efficient than HPS? No, it is not. Actually HPS is 1,5-2 times more efficient in generating photons than plasma light. But the HPS light quality is really bad. That sounds like a catch 22. Either you have good light and bad efficiency or good efficiency and bad light! FOR A SOLUTION WE GO BACK TO THE GREENHOUSES If you understand that you need a minimal amount of additional quality spectrum to guarantee a healthy crop (just like in the greenhouses) you would like to bring in some additional spectrum, at least to complement the blue light up to 7%. Also you want to introduce all the colors that HPS is lacking, basically all under 560 nm. A 300W LEP can provide just that in combination with up to 1,200 W HPS light. This does not re-create the full solar spectrum and still has more red light in it, but it is sufficient for a healthy crop. It all makes sense. In greenhouses you need a percentage of quality sunlight to guarantee a healthy crop when using HPS lighting, in climate rooms you create that sunlight by adding LEP to an appropriate level. LEP extras are the UVA and UVB in the spectrum you normally don’t get in a greenhouse because of the glass roof which shields UV in most cases. (Greenhouses) Supplemental spectrum (41.01) – specifically developed to add quality spectrum in combination with HPS light, adding the spectrum that the HPS lacks. Gavita Holland, a horticultural lighting company, introduced a LEP (Light Emitting Plasma) fixture which produces less red spectrum and more green and yellow for use in combination with HPS. (Garden Rooms, no sunlight) Grow spectrum (41.02 emitter). The STA 41.02 emitter provides high quality sunlight with a full continuous spectrum, and is most suitable for climate rooms and sun simulation. Unlike the HPS lamp the plasma lamp emits very little infra red radiation. High CRI full spectrum lighting for stand-alone use The original LEP with 02 emitter is also still available from Gavita and other LEP fixture manufacturers, and produces the best spectrum for a pure vegetative cycle or for artificial sunlight, for example for a dedicated vegetative climate room. It is still a good choice to use it with HPS, though the 01 green emitter has the advantage there. There is something to choose now when it comes to plasma lighting. The philosophy behind that is very simple: HPS is the most efficient technology to produce red light, so why would you want your LEP to produce this red spectrum when used in combination with HPS? The original LEP with 02 emitter is also still available from Gavita and other LEP fixture manufacturers, and produces the best spectrum for a pure vegetative cycle or for artificial sunlight, for example for a dedicated vegetative climate room. It is still a good choice to use it with HPS, though the 01 green emitter has the advantage there. There is something to choose now when it comes to plasma lighting. Gavita Light Emitter Model difference, used to illustrate main source light and supplemental light aspects with plasma lighting. Gavita is at this time the only lighting company to the time of this writing that I have seen use this aspect ethically with respects to marketing and in how to use and manage the light technology. I acknowledge that aspect due to its rarity in the industry. Sunlight Excerpts taken from discussion between Iunu, a light company and Gavita an agriculture lighting company at Garden Culture, a media company. Both companies sell plasma lights. These are excerpts from that discussion. Suggesting that plasma lighting saves you electricity is misleading. They do not replace a 1000W, or even a 500W HPS fixture. Plasma is a great source of supplemental light to add quality to your crop, but it is not the most efficient technology and people should understand that. Seed breeders, universities and research centers use our full spectrum plasma light in large installations for sunlight simulation, not for efficient grow lighting. This information is largely taken from an article republished from Garden Culture Magazine, Issue 1 under the title, “Light Emitting Plasma in Climate Rooms”. Theo Tekstra is the Marketing Manager for Gavita Holland BV. Hempyfans view on Plasma and LEC Metal Halide Lighting. As any light I see it as a tool in the gardener tool box. However, getting an understanding of this light and LEC Metal Halide lights is far more difficult than is believed. This is due to most of the information regarding these lights in the gardener community comes from lighting manufacturers who are generally as believable as a television commercial. They want your money, not to educate you so that you will make an informed and truly competent decision as you might then go a different way. The "facts" stated by marketing of lights are often created similar to how "political facts" are justified and often the use of misdirection aspects are employed to guide the potential buyer for the sales purposes. As a result the basic view point to understanding of the reality of lighting is often incorrect to some degree by many in the home to hobbyist gardener communities. This compilation and writing is designed to help light the subject so that we can better understand to a degree of appreciation of this technology and how to understand and use the varied spectrum from manufacturer to manufacturer. Generically, I prefer the professional agriculture industry to the grow shop specialist. Optimum use I see plasma lighting the way Gavita claims it to be best used. Used in supplemental lighting situations and/or in conjunction with HPS for higher quality plants. Value of your plants may determine how feasible this addition is for your crop. Better for small to middle plant sizes due to lack of strong light penetration of plasma lighting. This may become less an issue as technology matures and develops further. Secondary considerations Main Light plasma lighting could be an option for low/short to middle size plants due to low light penetration. Check for acceptable par ratings at distance for specific lamp capabilities. Lower heat than HPS. Potential better use if summer crops are a problem heat wise. Plasma still creates heat but less than HPS and can be air cooled or passively cooled. Other options to consider when evaluating plasma light use are LEC Metal Halide and LED full spectrum lighting. LED Lighting Technology LED lighting is a lighting option in growing that many growers have strong have opinions on, for and against. Many of these viewpoints both have merit in certain situations, for and against. Additionally, LED lighting when it entered the growing light marketplace was heavily hyped and what was a delivered at its initial best was a weak vegative light claiming to be a superior product and/or the equal of metal halide and hps lighting. As a result of this technology exaggerated capabilities and marketing tactics those who entertained this new technology was in essence harmed or worsened for the experienced. It is with this understanding and that I speak further, as what I say now is to directly discuss the light technology for what it is capable of in its current state of the year 2016. I personally stand by what I write now about LED at this time. As time goes on I cannot say how the opinion will alter on the state of the technology as the industry continues to evolve. ~Hempyfan, 2016 We will not pay any attention to comparison to other lighting options as this is a false way to understand the light as this is a marketing trick. However, due to the merchant industry tendency to make comparisons for marketing tactics so that people (consumers) can relate I do not look overly ill on this aspect as it is more a result of the nature of business rather than a concerted effort of the technology to gain acceptance by automatically claiming a quality status without achieving the status via merited experienced achieved by the technology being successfully used to the point it obtained ethical acceptance. Today I believe their are LED companies who have achieved this level of quality. However, to remain ethical as to the remarks I have made I will not name LED brands or companies that I personally like but I do give you the understanding as to how to select them. Please under the LED photos are for illustrative purposes and not an endorsement or a slick way of showing favor. Understanding LED technology is to understand what it can and cannot do. Low Heat compared to many other lighting options. Beneficial In hot environments or hard to control temperature grow areas. Consideration when other lights require additional cooling. LED can still require cooling depending on situation. Some models have very good penetration of lights Higher wattage Pay attention to the style and/or if any vegetable grows are quality documented as a reference. Some models have very good par ratings and spectrum ratings Some perform as a Main light Total Cost + Heat Management (temperature effects and actual cost) + Spectrum + Penetration + specific role of light divided by your unique limitations (budget etc) = Best Practice Main Light and the area for which you selected. So you have up to 2 light selections, Best practice (few can achieve but you can see what it will take to achieve and work towards that over time) Generally high cost in lighting and infrastructure. Generally high operating cost. Requires advanced knowledge to maintain. Some people will pay for a professional garden but they do not understand it and marketing eventually convinces a majority of these people to go into those directions and/or without knowing how to best manage the infrastructure they can alter the garden environment from best practice to some other measurement. Your informed decision on the light for your range of realistic options for you You understand the spectrum, the penetration and know what to expect from the light. You also know how to work towards "best practice" over a time. By better answering the limitations in the formula that prevented you from achieving initial best practice you inherently better yourself towards that goal. This is an additional benefit of actually making these plans before hand. Few appreciate this benefit and they are often wowed about how I can explain with precision how to better "dial in" their garden areas. ~Hempyfan. Consider heat aspects of all lighting options. Consider all cost associated with all lighting options. Consider light spectrum for what is acceptable Some perform as Main Vegetative or Main Blooming lights Full spectrum lighting White light more sun like Spectrum ranged (veg or bloom but not both) but not specifically designed for a short period development purpose. multi colored led lights or pink light for example. Designed Spectrum (purpose lighting, blue, red, transitional lighting, seedling lighting, mother plant lighting etc.) This type of LED perform as specialized additional lighting Assist in growth stage in achieving "best practice" in maximizing and achieving quality spectrum levels. An advanced aspect of some specialty and connoisseur gardeners and is not necessary for most garden vegetables. Assist in spot lighting for additional lighting of weaker light areas (traditionally corners and edges of light footprint) in the garden area. Rare situation, better assist improved light spectrum for unique or difficult plants that others within the grow area do not. May assist with hard to clone plants. Idea is light spectrum + environment + nutrition that matches ideal conditions to create the total environment that particular plant wants best for the purpose of which you are trying to achieve with that plant. Such as to root consistently when otherwise it was more difficult to successfully accomplish. Other lighting options are available to achieve this same effect. Consider heat aspects of all light options. Consider "all" cost aspects of all light options, initial and ongoing (electricity and bulb cost if applicable) LED Summary I have seen good and bad with LED lighting. I believe that LED technology is beginning to take its place within the industry. But like anything else. It is a tool and their are situations where LED lighting is not a wise option and at times it is. I have worked to try to give the technology a realistic writing as I see it. I invite you to use the above information in your judgement and see if it makes sense for you or not. I am not advocating for the purchase or to dissuade a purchase in LED products. I am advocating for understanding the technology and applying that understanding when you are evaluating lighting aspects and/or making lighting decisions. I do believe the technology, quality dependent and/or in situational use, has earned its place at the table for discussion. Like all specialty tools in a the tool chest, it is a tool option available to the indoor garden ranging from the simple to the complex. How much so, depends on you. Grow Calculators should only be used for a general range in figuring. Consider it a good general estimate. Click for LED calculator Union Break Never, argue with the Union! Well, when it comes to the Union Breaks you dont! The Florescent Family Standard florescent lights (shop lights) CFL - Compact Florescent Family/ HO - T5 High Output florescent lights VHO - Very high florescent lights Standard florescent lights (shop lights) I do not recommend standard T5 light fixtures (shop lights). Can be used for seed starting and clone rooting where low level light is required. Best Practice would be to use a full spectrum light or a vegetative adjusted spectrum light instead. HO - T5 High Output florescent lights & CFL Compact Florescent Lights T5 HO florescent lights have been a mainstay for many gardens. From starting seeds and cutting, to vegetative use to flowering their is much information available on how to successfully use these lights I will not spend overly to much time discussing it. With the availability of other lighting options that fit this category with different spectrum aspects I consider this a lower option in terms of quality of light. For financial constraints, this lighting technology may still be an attractive choice. It is a great tool in the light tool box and understanding it will enable you to use these to the best of their potential and serve you well as they classically have others for many years. This is a proven light. Common uses are in vegetative stages before moved on to stronger lights. Good for small to mid size plant gardens and low ceilings. Low light penetration Keep close to canopy/top of your plants 6 to 12 inches, plant and phenotype can vary. Good for additional supplemental lighting. Assist with dark spots in grow area assisting main light source for light distribution aspects. Developmental lighting addition to main light for spectrum to enhance a specific growth period of the plant. Such as adding more blue light or red light depending on plant stage. Vegetative and Flowering spectrum bulbs. Bulb quality and length of life varies from manufacturer to manufacturer. Variety of Florescent information. Practical Use Good side lighting illustration in use of CFL and other CFL uses. Induction Grow Lighting Induction Grow Lighting are the biggest option for Indoor Gardening in the florescent family range. This lighting category has a bad wrap for making the claims that 400w induction is same or better than a 1000w HPS. I have not been able to find spectrum and par information for Induction technology at this time but will update as I do. As any tool in the lighting tool box it is all about understanding this light and how best to utilize it. Low Heat compared to HPS (often this light is considered when looking at HPS options) 4x4 foot print. Light is straight down compared to HPS that is angled. In multiple HPS light setups or similar where you have light overlap at the edges, This address the angled light aspect of HPS lights. Induction companies misdirect this information. long life of bulb Expensive bulbs and requires vegetative and bloom bulbs for a whole crop. Can take into consideration the cost of other bulb replacements and life of bulb. This information is likely figured in to bulb pricing. Hempyfan's Induction Light Opinion It s my view that induction lighting generally attractive due to a variety of reason. However, understanding the light and how to use it will enable you to make the decision for yourself as your situation might benefit. Good for vegetative growth of 4x4 area. A good staging light for rooted plants in vegetative growth before going into flowering. Smaller heat footprint but in summer months can require some cooling. Due to cost of bulbs, I cannot easily recommend this light for vegetative and bloom stage. Due to other full spectrum light options at low price points I cannot recommend. Spectrum and par ratings are hard to find for induction lights. This is an indication of potential marketing hype and misdirection. Assembly aspects of an induction light. Gives some good information regarding induction. Growing Calculators Grow Calculators should only be used for a general range in figuring. Consider it a good general estimate. Click to visit Calculate at Maximum Grow Gardening Site. What's in The Calculator Wattage Calculator: Use this to determine the light wattage you will need for your size grow room. Parts Per Million Calculator: Use this calculator to determine accurate solution mixes. Carbon Dioxide(CO2) Calculator: Calculate how much CO2 will be needed to fill a grow room to the optimum level. Temperature Converter: Use this to easily convert between degrees Celsius and Fahrenheit. Air Exchange Calculator: Enter your grow room dimensions, and this will tell you how powerful of a fan you will need for optimum air flow. Estimated Cost Calculator: Predicts how much the cost for electricity will be monthly. What's that light cost you? Click to visit the calculator located at Dark Sky Society You can calculate results for up to four types of lights. http://www.darkskysociety.org/lightcost/index.php Select the type of lamp (i.e. Incandescent, Fluorescent, etc.) Select the lamp wattage (lamp lumens) Enter the number of lights in use Select how long the lamps are in use (or click to enter your own; enter hours on per year). Finally, click submit on the calculator at the site and find your answer. BTU Calculator, click Eye Hortilux to visit their calculator. (the recommendations in heat was based on this calculator.) A BTU, also known as a British Thermal Unit, is a measurement of the energy needed to cool a substance. Grow lamps generate a lot of heat. By converting your wattage into BTU per hour, you’ll have the information you need to keep your plants cooled so that they don’t burn up from the heat of the grow lamps. Reflector/Hood Types Horizontal Reflectors are the most popular option as its the most traditional style of growing. Selecting the type of reflector will largely depend on your environmental temperature and how you are planning to control the heat generated from the light. Select reflector that best matches your grow style and methods. Such as a wider light spread vegetative growth Such as a parabolic reflector Such as a winged reflector Flowering growth. Commonly air cooled/enclosed hoods Not necessarily best practice Open hood without glass Likely this requires air conditioning of some type or method. winged reflector Standard and basic reflector type. parabolic reflector High spread of light or focuses depending on height from canopy. https://en.wikipedia.org/wiki/Parabolic_aluminized_reflector_light Internal Ballast For growing areas 2x2 feet and smaller, it may be more suitable to have a reflector with the ballast mounted inside the reflector (internal ballast). This is beneficial with little space in small tents and a areas. This is usually how the 250 watt systems are sold. Not directly light related but is relevant to subject. Air-Cooled/Enclosed Hoods If a grow room is too hot than air cooled may be an option. Commonly used with 400 to 1000 watt HPS and 400watt metal halide light in a tent/closet or many lights in a room this maybe a consideration. An Air-cooled light has duct holes in the reflector to connect duct tubing and an inline fan for venting out the heat. These are available from the 4, 6 and 8inch duct sizes. Hood Sizes and type The hood for a HPS light will largely depend on your environmental temperature and how you are planning to control the heat generated from the light. Air cooling is not best practice but is trade-off for better cooling in some situations. required inline fans and/or ducting fans are used and also generate some heat in their operation adding to ambiant room temperatures. Insulated ducting could assist with heat management in certain situations. Insulated hoods or water jackets can also be helpful in certain situations. It is generally better to go with a lower wattage light and manage a better grow environment than add more light and subject the plants to an uncomfortable grow environment. A hoods glass cover diminishes the effectiveness of the bulb output. You earned for finishing Section II Click for - Advanced Section III - Lighting & Reflector Section http://culturalhealingandlife.com.www413.your-server.de/index.php?/topic/8-section-iii-plant-growth-and-light/ ~ Hempyfan, A proud HD writing & compilation.