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  1. #1
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    Measuring Light Efficiency

    0 Not allowed!
    Here is a bit about light measurement I found on the site. It is very good information about how plants use light.
    11 September 2011
    Lumens are for humans
    Posted in Technical papers


    Many lamp manufacturers still specify the output of their lamps (illuminance) in lumens, though this just specifies how we humans percieve the intensity of that light. Our eyes are most sensitive to green ligh of 555 nm, but plants are more sensitive to a much broader spectrum. So what is the right way to specify horticultural lamps and how can you calculate with that? What's in it for you? Enter the photons.
    PAR spectrum

    Plants primarily use the light ranging from 400-700 nm bandwidth (violet to far red). The light within this bandwidth is called Photosynthetic Active Radiation (PAR). So the bandwidth of the light that plants are sensitive to is much broader than what we see. Using lumens, which are measured according to what the eye is sensitive to, is therefore not a correct representation of the grow light properties of a lamp.


    Scientists proved that there is a relationship between the number of photons and the photosynthesis: It takes about 8 - 10 photons to bind one CO2 molecule. They also discovered that there is little difference in the effectiveness of blue or red light. So there is a direct relationship between the number of photons in the PAR spectrum and the photosynthetic potential of a plant (and ultimately the yield of a plant).

    For many years now professional researchers have used photon counts in the PAR spectrum as a standard and the greenhouse industry followed very quickly. Most European horticultural lamp manufacturers specify the output of their lamps in PAR photons per second. Because photons come in large numbers we uses a multiplier, in this case Avogadro's constant (6,0221415 × 1023) to get an expression in mol. 1 mol photons is 6.0221415 × 1023 photons. Now that's a lot of photons and to get that to levels that become easier to comprehend they are divided by 1 million, thus creating micro-moles (µmol). So 1 µmol is 6.0221415 × 1017 photons.

    To illustrate why µmol work a lot better for us: the PPF of a 600W HPS lamp is about 1100 µmol/second. If you would express that in moles it would be 0,0011 mol/s. Now that's a bit more difficult to calculate with.

    Photosynthetic Photon Flux (PPF)

    Photons are counted per second as we count a flow or flux of photons. If you count all the photons that a lamp emits in the PAR spectrum per second you get the Photosynthetic Photon Flux (PPF). The only way you can measure this accurately is in an integrating sphere, the Ulbricht sphere. So the PPF is measured in µmol/s and represents all the photons in the range of 400-700 nm per second. But how much ot that will reach your plant and at what distance?

    Photosynthetic Photon Flux Density (PPFD)

    Let's say we mount the lamp in a really good horticultural reflector, which has a total efficiency of 95%. That figure means that of the original 100% light of the lamp, 95% is totally emitted by direct light from the lamp or reflected light from the reflector. You could also say your reflector losses are 5%. Now if you spread your 1100-5% on a surface of 1 square meter, you would irradiate 1045 µmol/m2/s (1045 µmol m-2 s-1). This is called the Photosynthetic Photon Flux Density. If I would move closer to the source and would just light half a square meter the irradiance would be 2090 µmol m-2 s-1. And of course spread over 4 m3 you would get 261 µmol m-2 s-1. Double the surface means half the PPFD. Just divide the PPF by the lit surface in m2 to get close to the calculated PPFD. You will always have some stray light losses (much more with open reflectors!) and you have influence by the reflection of the walls, which causes a loss.

    PPFD you can easily measure with a quantum meter and a sensor that is specifically designed for the PAR spectrum. Unfortunately real quantum meters are expensive. The Li-Cor meters are used throughout the industry and are recommended. Most meters under $500 use lumens sensors and an internal table to approximate the PPFD in micromoles. We have found them to be inaccurate because they are still more sensitive to certain colors and do not take other colors within the PAR spectrum into equal account.

    And how about spectrum?

    PPF and PPFD only qualify the amount of photons, and not the quality of the spectrum. If spectrum was not important you would be able to grow any plant under just a single color red LED for example. Plants need different colors for different processes. The color of the light specifically influences the shape, build and development speed of the plant. In greenhouses the sunlight provides quality light. The HPS lamps are just used for extra photons, for quantity. So yes, spectrum is important, specifically when growing indoors where there is no sunlight. Plants have developed under sunlight for millions of years so you can expect them to be adapted for that spectrum and they use all of it as efficient as possible.

    Calculating with micromoles

    If you know how much light you require for optimal growth of your plants it is easy to calculate how much lamps you need. There is one complicating factor, and that is walls. Walls reflect only part of the light, as low as 40-50% depending on the reflective material. When using diffuse reflection materials not all of the light reflected will reach your crop. So there are serious losses at the edges of your grow room. The bigger the grow room, the less the wall effects. One way to solve the problem is to keep your final fixtures closer to the wall than half the distance between fixtures in the room to allow for some more direct light and reflection at the sides to even out the overlap. An adjustable reflector that sends the light down at the wall side can save you a lot of light.

    When you have a room with many lights you will have a great advantage when you overlap your light. Hanging your lamps higher from the crop will create a bigger spread and a lower PPFD per fixture, but you can add the overlap from the other lights so you will still have the same light on your crop but at a greater distance. This is much easier for climate control and a more uniform light coming from different directions, enabling a better penetration in your crop.

    Roughly these are a few examples of recommendations for a high light recipe of around 700 µmol m-2 s-1. Calculations made with 10% reflector / wall losses:

    400W a) - 1 x 1 m - 1 m2 at a ppfd of ~ 650 µmol m-2 s-1
    600W b) - 1,2 x 1,2 m - 1,44 m2 at a ppfd of ~ 690 µmol m-2 s-1
    1000W c) - 1,5 x 1,5 m - 2,25 m2 at a ppfd of ~800 µmol m-2 s-1

    In practice levels can be lower with different reflectors (open reflectors will have more stray light), older reflectors and a lot of wall influences. Other lamps may result in different densities.

    a) - Philips GreenPower 400W 230V - ppf 725 µmol
    b) - Philips GreenPower 600W 230V - ppf 1100 µmol
    c) - Philips GreenPower 1000W 400V Electronic - ppf 2000 µmol
    “Make the most of the Indian hemp seed, and sow it everywhere!” George Washington
    "The War on Drugs has no greater enemy than science" Jorge Cervantes

  2. #2
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    0 Not allowed!
    thanks for posting. nice information. - greetings

    btw if i got that right a 600w bulb binds 7485521884500 CO2 molecules/second
    2 months of flowering gives me 2538000 seconds of light (12/12) x 7485521884500 CO2 molecules
    that's 18 998 254 542 861 000 000 bound CO2 molecules or did i missed a factor ? i need some skunk now anyway


    Determine the number of moles of CO2 in 454 grams.


    First, look up the atomic masses for carbon and oxygen from the Periodic Table. The atomic mass of C is 12.01 and the atomic mass of O is 16.00. The formula mass of CO2 is:
    12.01 + 2(16.00) = 44.01
    Thus, one mole of CO2 weighs 44.01 grams. This relation provides a conversion factor to go from grams to moles. Using the factor 1 mol/44.01 g:
    moles CO2 = 454 g x 1 mol/44.01 g = 10.3 moles
    'the more you look into the living nature, the more wonderful you will recognize it'
    albert hofmann

  3. #3
    Marijuana Growing Member
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    Somewhere in the Aurora Borealisx Haze#5
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    0 Not allowed!
    I think this is pretty much what Jorge was saying, This was taken from the website of one my hydro shops that I had been too.

    7-colour LED’s – why they work

    Plants, like most land-based life forms, need the correct spectrum of light to allow the process of photosynthesis and uptake of CO2 (one of the basic building blocks for life). They also need good humidity (high humidity opens the stomata, which is the pore in the leaf through which the CO2 enters the plant and Oxygen exits), humidity is not to be confused with condensation which is generally bad for the plants and causes mold and other problems, the plant also requires water and nutrients.

    LUX is a measure of “brightness” in a given area and Lumens are a measure lux over a 1M2. Spectrum requirements differ by species, but most herbaceous plants require light in the blue and red area’s of the spectrum. Lux places different weighting to different spectrums as related to the human perception of light, It’s most heavily biased towards 555nm, which is green in appearance (the area of the spectrum in which humans see the best). Unlike humans, plants do not require green light, which is why it’s bounced back at your retina by the plant when you look at it.

    Watts are an equally bad way of measuring light as Lux and Lumens are. It’s just a simple measurement of expressing the energy consumption of a given lamp or device etc. It does not tell you how much of the energy is being converted to something useful, just that the amount of “load” it will place on a given circuit. The only way to realistically compare one light source with another is by looking at the yield per watt/per meter, but even this ignores all the other variables that relate to it, like ambient temperature and background CO2 and humidity levels. For this reason, the use of 3w LED’s or 1w LED’s is a bit of a red herring, the wattage will dictate the intensity at the point of generation, not at the leaf surface, where it matters. That said, 3w light arrays are cheaper to manufacture and for this reason, the market is moving towards them.

    Unlike LUX and Lumens (which have a direct relationship to the human perception of brightness), UMOL/M2/s is a unit for PPFD, PPFD is an abbreviation of Photosynthetic Photon Flux Density. This measure looks at the spectrum from the perspective of the plant and measures the volume of the light provided by the light source, over a given space and instant in time.

    PPFD is a measure of light quantum (photon quantity) of photo-synthetically active radiation, light energy of an appropriate spectrum, which reaches, in a given time and over a given area, the surface of the plant. Plants speed of photosynthesis depends on the light quantum (photon quantity) absorbed by the plants. You can think of the stomata as the plants mouth for the consumption of CO2, which is stimulated to open by the light landing on the leaf surface and the roots are the plants mouth for nutrients. PPFD is a measure of the availability of the correct food (light spectrum) in a moment in time and over a fixed area of the plants foliage.

    If the light (of the correct spectrum) was water contained in a watering can, you can pour it out of the spout very quickly into a small area if you do not use a rose on the end. However, if you attach a rose to the spout, you can pour the same amount of fluid out of the can in the same time, but over a greater given area. Light is measured in this way using PPFD, as it looks at the speed and quantity of the delivery of the light, whilst considering the spectrum and the area covered.

    When the optical radiation intensity (PPFD umol/M2/s) reaches the highest point (also called the light saturation point), plants have the quickest carbon dioxide exchange speed (carbon dioxide absorption and oxygen release). Carbon Dioxide (CO2) is a material required for photosynthesis as the plant uses it to build cells, be they leaf, flower, root or stem cells. They all require CO2 to make them happen. For example, the light saturation point for many common herbal plants is 1512 umol/M2/s). When it reaches 1512umol/M2/s, it’s at its maximum carbon dioxide exchange rate. This means the plants grow bigger, faster.

    LED’s have always been good at getting the right spectrum out, but they were really bad (until now!) at getting the light they produced to the plant, they couldn’t penetrate the space in front of them and get to the plants leaf surface to make a real difference. Now the latest generation of LED’s contain lamps that will penetrate up to 2M and produce a 7-colour spectrum that is perfect for your plants to thrive in. Pink or purple in appearance, these lights do not waste energy producing spectrum your plants can’t use (like green).

    In order to get the best results from the new generation of LED lights they have to be used correctly. The umol/M 2/s of the AREA 51 234w (78x3w) 7-colour lights is 756umol/M2/s each, so if you use two of these lights in 1M2 tent, you will be producing enough of the correct light to produce 100% of the plants maximum possible yield in a M2 (all things being equal, like temperature and other environmental variables).

    The use of 1 of these LED lights is likely to produce less than might be expected from a single Sodium based HPS lamp of around 400w, but that is for the reasons outlined above. However, the use of a single 234w AREA 51 7-colour LED in an 80x80x200cm tent (36% of the area of a 100x100x200cm tent), you can expect to exceed the HPS method significantly. Not least because the 400w HPS is likely to cause significant issues as a result of heat and the resulting transpiration rate (sweating) of the plants, leading to nutrient burn and shock.

    The 90w AREA 51 light produces 291umol/M2/s per lamp and this area of foliage (80x80cm) could take up to 544umol/M2/s, so 2 x 90w would produce slightly more (7%) than required for this space. A single 234w AREA 51 would produce 39% more than can be absorbed, wasting energy and money over the long term

    The umol/M 2/s of the LED’s is also complemented by the reduced stress the plants feel, the lack of fan noise (from the fans going at full tilt, trying to get the heat of the HPS out the room), the reduced nutrient and water requirements of the plants. More easily controlled CO2 systems and humidity controls. You can also expect 20-80% energy saving (depending on the amount of lamps and what they are compared against (HPS or CFL etc.)).

    LED’s have had some rightly deserved bad press in the past, but that was because the lamps were not at a stage of development that would deliver on the high expectations the market had. This is no longer the case as repeated tests have demonstrated, it’s a case of changing what you do and how you do it, this way the technology delivers, rather than disappoints! The future of the LED is assured, growers will feel and see the benefits and the plants will yield the results we all want.

    If you want the link, I will be happy to post that too.
    Last edited by watcha; 02-12-2013 at 01:36 PM.

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