This website had a bunch of helpful information not only about LED lights, but on all lighting. Has a number of good charts and even information as to how plants absorb light at different NM levels.

http://www.littlegreenhouse.com/guide3.shtml

Seoul Semiconductor’s LED for Agricultural Lighting in Japan
Seoul Semiconductor Co., Ltd. has supplied LEDs emitting red and blue light to “A” company in Japan, and introduced their advanced technology and products at ‘LED Farming Demonstration Project’ organized by Minister of Economy, Trade & Industry of Japan.

LED light source for farming is getting popular for energy saving and improvement of product quality.
This ‘LED Farming Demonstration Project’ held at the lobby floor has been planned by the local economy & industry group of Minister of Economy, Trade & Industry of Japan in order to inform the possibility of LED as a new farming light source and the new LED-related technology to the public and the officials of that ministry.

Z-Power LED products of this company have been supplied to ‘A’ company which is a major participant in this project, in order to produce LED lighting fixture samples, and 300 thousand pieces will be shipped more. The products of Seoul Semiconductor used for this project emit red and blue lights, as the artificial light source helping the growth of plants.

A staff of ‘A’ company said, “This project focuses on the LED lighting fixtures for farming which have high brightness LED with high light quantum, and especially optical wavelength of red and blue light can hasten the growth of plants so that enables stable harvesting from vegetable farming.

By participating in this project, Seoul Semiconductor confirmed their competitive power in the Japanese market having advanced technologies, and the possibility to expand the LED market as a lighting source for farming. This is expected to be a starting point in developing new markets. With artificial light source, the quality and quantity of plants may increase through farming without agricultural chemicals and influence of weather, leading to higher income of farm families. In the past, incandescent lamps, fluorescent lamps and sodium lamps have been mainly used, but in the present time, eco-friendly LED of high efficiency and long lifespan without carbon discharge is being popular. Also Seoul Semiconductor has supplied LEDs for agricultural lighting in Canada.

According to the report of Rural Development Association of Korea, assuming that we cultivate crops with supplementary lighting in about 3,000 ha by using LED, we can get 70% energy saving effect compared to incandescent lamps, which amounts to $12M per year. Especially, farming with artificial lighting became possible even in a dessert or the Artic region. Therefore, it is expected to be helpful to remove food problems over the world.

About Seoul Semiconductor:
Seoul Semiconductor, a world leading LED manufacturer, has been named in Forbes and Business Week's lists as one of the most promising Asian companies. Its main offering, the Acriche™ LED, was also named "Product of the Year" by Elektronik in 2006, one of the most prestigious electronics publications in Europe. In 2008, this award was given again to Seoul Semiconductor's Flash LED product. Acriche, developed in 2006, is operated directly through AC current without any converters needed for DC LED operation, extending the LED's life span and making installation costs easier and less expensive. With these important benefits, Acriche LED technology is expected to pioneer the future of the lighting industry. With its cutting-edge technology, Acriche has been awarded in Newtech Korea 2008 and named as Korea Ten Best New Technologies of 2008. Seoul Semiconductor's primary business areas are LED packaging and custom module manufacturing. It provides a full range of LED products including AC-driven semiconductor light sources, Acriche brand products, High-Brightness-Power products, Side-View LEDs, Top LEDs, Chip LEDs, Lamp products, High-Flux LEDs, and custom-type modules. Applications for the company's LED products include general lighting, signage, back lighting for mobile phones, TVs, notebook computers, automotive lighting, home appliances, signals, etc. Seoul Semiconductor reported KRW 284b in sales in 2008. It filed and registered over 5,000. Seoul Semiconductor has 25 branches including 3 overseas corporate offices. Its products are also represented by more than 114 worldwide distributors.

if you really want to make your head hurt check out this website, http://www.led-professional.com/

http://autolumination.com/colors.htm

Notes on LEDs
LED Parts
LEDs come in all shapes and sizes, but the 3mm T-1 or 5mm T-1¾ are the most common.

The die is a small cube of semiconductor. The composition of the die determines the color of the light given off. The die sits in the top of the die cup, which is a reflector to reflect the light emitted by the die. The beam angle is determined by the shape of this relector. The epoxy body also is shaped to acts to effect the focus and appearance of the the light beam. The distance from the die cup to the domed end of the lens determines how tightly focused is the resulting beam of light. Some LEDs have flat, opaque, or even concave ends to help disperse the light into a wide beam.

LED Color
Visible LEDs

Wavelength
nm Color
Name Color
Sample
over 1100 Infrared
770-1100 Longwave NIR
770-700 Shortwave NIR
700-640 Red
640-625 Orange-Red
625-615 Orange
615-600 Amber
600-585 Yellow
585-555 Yellow-Green
555-520 Green
520-480 Blue-Green
480-450 Blue
450-430 Indigo
430-395 Violet
395-320 UV-A
320-280 UV-B
280-100 UV-C
LED colors are often specified in "nm", or nanometers, which is the wavelength of the light. The wavelength given is the wavelength at peak output. LEDs are not perfectly monochromatic, but rather produce a range of wavelengths over a small region of the spectrum. The graph on the left shows color vs. intensity for a typical green LED. Notice the peak is at about 565 nm, but it is actually emitting light over a range of about 520 nm to 610 nm. Spectral line half-width is the width of this curve at 50% intensity (0.5 on the Y-axis). For this LED, it is about 30 nm. Spectral line half-width is a measure of how "pure" (monochromatic) the color is.



Notice the temperature (Ta) given in the upper right corner of the graph. LEDs emit slightly different colors at different temperatures. They also emit different colors at different currents, especially white LEDs which depend on phosphors to change the colored light of the die to white light.

This is why white leds (in particular) will never match perfectly in color.

Infrared LEDs
The infrared band can be divided into Near Infrared (NIR) and Far Infrared (IR). Far infrared is the thermal infrared used to detect hot objects or see heat leaks in buildings, and is way beyond the range of LEDs. (NIR can be further divided into two bands, longwave and shortwave NIR, based on how film and CCD cameras react.

Infrared LEDs are sometimes called IREDs (Infra Red Emitting Diodes).

Ultraviolet LEDs
Ultraviolet light is divided into three bands: UV-A, which is fairly innocuous; UV-B, which causes sunburns; and UV-C, which kills things. Most UV-B and all UV-C from the sun is filtered out by the ozone layer, so we get very little of it naturally. LEDs emit UV-A.

400 nm is a pretty common wavelength for UV LEDs. This is right on the border between the violet and ultraviolet, so a significant portion of the light emitted is visible. For this reason 400 nm UV LEDs are sometimes rated in millicandela, even though as much as half of their energy is invisible. LEDs with lower wavelengths, such as 380nm, are usually not rated in millicandela, but in milliwatts.

YOU SHOULD NOT STARE INTO ANY LED DUE TO ITS BRIGHTNESS. MOST LEDS WILL INVOKE PAIN TO THE EYE TO WARN YOU TO LOOK AWAY. ULTRAVIOLET LEDS ARE PARTICULARLY DANGEROUS, BECAUSE A LARGE PORTION OF THE RADIATION EMITTED IS IN THE VISIBLE RANGE. THE RESULT IS THAT YOUR EYES WILL NOT INVOKE PAIN TO WARN YOU THAT THEY ARE HARMING YOUR EYES.

White light is a mixture of all the colors. Color "Temperature" is a misnomer and is not understood by most people. This is not helped by all the false advertising and hype that is used by marketers to sell their products. Color "Temperature" is a measure of the relative amounts of red or blue light being emitted. It is not a measure of temperature at all.

Higher color temperatures have more blue. A higher color temperature, is not necessarily an indication of a higher quality, or more expensive light. It is not a brighter light. If you want super high color temperature, just buy a blue light. It is has infinite color temperature which is higher than any "super or hyper" white light.

Kelvin Color Scale



Color
Temperature Common Example
2000° Gaslight
2470° 15 watt incandescent bulb
2565° 60 watt incandescent bulb
2665° 100 watt incandescent bulb
2755° 500 watt incandescent bulb
2900° 500 watt Krypton bulb
3100° Projector type filament bulb
3250° Photo Flood
3400° Halogen
3900° Carbon arc
4200° Moonlight
4700° Industrial smog
5100° Hazy weather
5500° Sun 30° above horizon
6100° Sun 50° above horizon
6700° Electronic Flash
7400° Overcast sky
8300° Foggy weather
30,000° Blue sky



Remember that this is a measure of color, not brightness, so don't freak out because moonlight is "hotter" than a carbon arc! It just means that the color is bluer, that's all.

White and blue LEDs have a color temperature, but leds not in the white-blue spectrum do not.

LED Brightness
The total power consumed by a light is measured in watts. How bright the object appears, however, will depend on two additional factors:

how much radiant flux is emitted toward the observer; and
how sensitive the observer is to the wavelength(s) of the light.
To quantify the first, the steradian, a solid (3-D) sphere is used.

If the radiant flux of a source is radiated uniformly in all directions, the radiant intensity will be simply the total radiant flux divided by 12.57 (4π) steradians, the solid angle of a complete sphere. In the case of LEDs, the radiant flux is usually concentrated into a beam, however, so the radiant intensity will be the radiant flux divided by the solid angle of the beam. Beam angles are usually expressed in degrees, while radiant intensity is usually expressed in mW/sr, making a conversion from beam angle to steradians necessary:

sr = 2 π (1 - cos(θ/2))

where sr is the solid angle in steradians, and θ is the beam angle.



Beam Angle °
Beam Angle sr

Luminous flux and luminous intensity are measurements like radiant power and radiant intensity, only adjusted for the sensitivity of the human eye. Radiant power of a wavelength of 555 nm is multiplied by a factor of 1, but light of higher and lower wavelengths are multiplied by lower factors, until infrared and ultraviolet wavelengths are reached, when the radiant power is multiplied by zero.

Luminous flux is measured in lumen, while luminous intensity is measured in lumen per steradian, also called a candela.

The relationship between luminous flux, luminous intensity, and beam angle means is that focusing a given LED into a tighter beam (decreasing the beam angle) will increase its luminous intensity (brightness) without actually increasing the luminous flux (amount of light) it puts out. Keep this in mind when buying LEDs for illuminating purposes - a 2000 mcd 30° LED puts out just as much light as am 8000 mcd LED with a 15° viewing angle. (The angle is half in both width and height, so the beam is four times as bright.) This is one of the reasons that ultra-bright LEDs are often "water clear", to keep the light going in one direction and not diffuse it all over the place.



Beam Angle °
Luminous Intensity mcd
Luminous Flux lumen

The brightness of LEDs is measured in millicandela (mcd), or thousandths of a candela. Indicator LEDs are typically in the 50 mcd range; "ultra-bright" LEDs can reach 15,000 mcd, or higher (the 617 nm Luxeon Star (part number LXHL-NH94) can reach 825,000 mcd), but the cost is these leds makes them not yet practical for common use.

By way of comparison, a typical 100 watt incandescent bulb puts out around 1700 lumen - if that light is radiated equally in all directions, it will have a brightness of around 135,000 mcd. Focused into a 20° beam, it will have a brightness of around 18,000,000 mcd.



38-11 Illumination

I ntensity of light and other electromagnetic radiation as power per unit area, measured in watts per square meter. Similarly, the total rate of radiation of energy from any of the sources of light discussed in Sec. 38-2 is called the radiant power or radiant flux, measured in watts. These quantities are not adequate to measure the visual sensation of brightness, however, for two reasons: First, not all the radiation from a source lies in the visible spectrum; and ordinary incandescent light bulb radiates more energy in the infrared than in the visible spectrum. Second, the eye is not equally sensitive to all wavelengths; a bulb emitting 1 watt of yellow light appears brighter than one emitting one watt of blue light.

The quantity analogous to radiant power, but compensated to include the above effects, is called luminous flux denoted by F. The unit of luminous flux is the lumen, abbreviated lm, defined as that quantity of light emitted by 1/60 cm² surface area of pure platinum at its melting temperature (about 1770°C), within a solid angle of 1 steradian (1 sr). As an example, the total light output (luminous flux) of a 40-watt incandescent light bulb is about 500 lm, while that of a 40-watt fluorescent tube is about 2300 lm.

When luminous flux strikes a surface, the surface is said to be illuminated. The intensity of illumination, analogous to the intensity of electromagnetic radiation (which is power per unit area) is the luminous flux per unit area, called the illuminance, denoted by E. The unit of illuminance is the lumen per square meter, also called the lux:

1 lux = 1 lm/m²

An older unit, the lumen per square foot, or foot-candle, has become obsolete. If luminous flux F falls at a normal incidence on an area A, the illuminance E is given by

E = F ÷ A

Most light sources do not radiate equally in all directions; it is useful to have a quantity that describes the intensity of a source in a specific direction, without using any specific distance from the source. We place the source at the center of an imaginary sphere of radius R. A small area A of the sphere subtends a solid angle [omega] given by [omega]=A÷R². If the luminous flux passing through this area is F, we define the luminous intensity I in the direction of the area as

I = F ÷ [omega]

The unit of luminous intensity is one lumen per steradian, also called one candela, abbreviated cd:

1 cd = 1 lm/sr

The term "luminous intensity" is somewhat misleading. The usual usage of intensity connotes power per unit area, and the intensity of radiation from a point source decreases as the square of distance. Luminous intensity, however, is flux per unit solid angle, not per unit area, and the luminous intensity of a source in a particular direction does not decrease with increasing distance.

EXAMPLE: A certain 100-watt bulb emits a total luminous flux of 1200 lm, distributed uniformly over a hemisphere. Find the illuminance and the luminous intensity at a distance of 1 m, and at 5 m.

SOLUTION: The area of a half-sphere of radius 1 m is

(2[pi])(1 m)² = 6.28 m²

The illuminance at 1 m is

E = 1200 lm ÷ 6.28 m² = 191 lm/m² = 191 lux

Similarly the illuminance at 5 m is

E = 1200 lm ÷ 157 m² = 7.64 lm/m² = 7.64 lux

This is smaller by a factor of 5² than the illuminance at 1 m, and illustrates the inverse-square law for illuminance from a point source.

The solid angle subtended by a hemisphere is 2[pi] sr. The luminous intensity is

I = 1200 lm ÷ 2[pi] sr = 191 lm/sr = 191 cd.

The luminous intensity does not depend on distance.



LED Brightness - IR and UV LEDs
Question: How bright is an IR LED?
Answer: 0 mcd.

Since candela and lumen are units that are adjusted to compensate for the varying sensitivity of the human eye to different wavelengths, and IR and UV are totally invisible (by definition) to the human eye, all IR and UV LEDs are automatically zero lumens and zero mcd. These units of measure, used for visible-light LEDs, can't be used for UV and IR LEDs (despite the "3000 mcd IR LED" currently on eBay).

IR and UV LEDs are measured in watts for radiant flux and watts/steradian for radiant intensity. A fairly typical "bright" IR LED will put out about 27 mW/sr, though they go up to 250 mW/sr or so. Signaling LEDs, like for TV remotes, are considerably less powerful.

HOWEVER - keep in mind that LEDs are not perfectly monochromatic. If their peak output is close to the visible spectrum, then their bandwidth may overlap the visible spectrum enough to be visible as a dim cherry-red light. Furthermore, some people can see further into the red region than can others, seeing as deep-red colors that to others are invisible infrared. While it would be possible to give such an LED a rating in millicandella, it would be misleading.

This dim red glow, by the way, is often claimed - wrongly - to differentiate good illumination IR LEDs from much dimmer IR LEDs. Which LED is better for such a purpose is totally dependant on the wavelength at which the receiver is most sensitive.

Using LEDs
As a rule of thumb, different color LEDs require different forward voltages to operate - red LEDs take the least, and as the color moves up the color spectrum toward blue, the voltage requirement increases. Typically, a red LED requires about 2 volts, while blue LEDs require around 4 volts. Typical LEDs, however, require 20 to 30 mA of current, regardless of their voltage requirements. The table on the left shows how much current a typical red LED will draw at various voltages.

Notice that this LED draws no current under 1.7 volts; the LED is "off". Between 1.7 volts and about 1.95 volts, the "dynamic resistance", the ratio of voltage to current, decreases to 4 ohms. Above 1.95 volts, the LED is fully "on", and dynamic resistance remains constant. Dynamic resistance differs from resistance in that the curve isn't linear. Just remember that this non-linear relationship between voltage and current means that Ohm's Law doesn't work for LEDs.

Notice how steep the slope is - almost vertical. LEDs have a much more vertical slope than do normal diodes (but not as bad as laser diodes).This means that a tiny increase in voltage can produce a large increase current, and lots of smoke. In the above-mentioned LED, 2 volts is required to drive the LED properly, but as little as 2.04 volts could destroy it. To keep the current down to a reasonable level, a series resistor must be included in the circuit.

The formula for calculating the value of the series resistor is:

Rseries = (V - Vf) / If

where Rseries is the resistor value in ohms, V is the supply voltage, Vf is the voltage drop across the LED, and If is the current the LED should see.

For example, the above LED would run very nicely off 12 volts with a 500 ohm series resistor. Since 500 ohms is an odd value, you could do almost as well with a 470 ohm resistor, which would let the LED draw 21 mA.

You can use a single resistor to control the current to a series of LEDs, in which case Vf is the total voltage drop across all the LEDs. You can sometimes get away with using a single resistor to control the current to a group of LEDs in parallel, but it's not generally a good idea - if there is any variation in the LEDs, they won't each draw the same current, resulting in differences in brightness - or in smoke.

Driving LEDs with AC
There are several factors to consider. One is that the LED will only conduct during that portion of the positive half of the cycle during which the voltage is above the threshold voltage of the LED. This means that the LED is conducting less than half the time, which will effect brightness.

Second, even when the LED is conducting, the average voltage will be far less than the peak voltage. The average voltage of the positive half of a sine wave is only 64% of the peak voltage. (Think "area under the curve.") Brightness is therefore further reduced.

This is what I mean. The X axis is time, the Y axis is voltage. The blue line is the supply voltage; the red line is the LED threshold. In this case, the peak voltage is 5 volts, and the threshold is 1.2 volts (typical for a red LED). The "effective voltage" (my term), is the voltage that is above the threshold voltage, the voltage that actually lights the LED; the rest of the voltage does nothing, either because it is under the threshold, or it's of the wrong polarity. Effective voltage is shown in the graph by the gray areas. The light gray area is the average effective voltage for an AC supply voltage; here, 1.04 volts. The dark gray area is the average effective voltage for a DC supply, 3.8 volts, that the AC supply voltage misses. The light gray area is a mere 27% of the area of both gray areas combined. If the LED had a threshold voltage of zero (wouldn't that be nice?) the effective AC voltage would still be only 32% of the effective DC voltage. As threshold voltage rises, the "duty cycle" goes down from there.

The effective voltage is the (V-Vt) term from the formula given above, and can replace it for calculating the value of the desired resistor.

You could increase the effective AC voltage toward the theoretical maximum of 32% of the effective DC voltage by increasing the supply voltage - this makes the threshold voltage a smaller portion of the peak voltage, so the LED turns on sooner in the cycle and stays on longer. But you have to avoid using a peak voltage greater than the reverse voltage that the LED can tolerate - typically only 5 volts. Remember that when the LED isn't conducting, all the voltage drop will be across the LED. You can sidestep this problem by including a separate diode - silicon diodes can withstand far more reverse voltage than LEDs can, although an additional diode will impose a second threshold voltage. Incorporating a full-wave bridge rectifier would let you drive the LED with both halves of the cycle, increasing the maximum possible effective voltage to 64% of that of DC, at the price of two additional threshold voltages.

Some white LEDs require forward voltages (typically 3.5 or 4 volts) very close to their maximum reverse voltage (typically 5 volts), so the LED will only be on for a very small fraction of the cycle, making it very dim. For example, an LED requiring 3.5 volts driven on 5 volts AC would only an effective AC voltage of only 0.25 volts, only 17% of the effective DC voltage of 1.5 volts.

To compensate for the low average effective voltage, we'd want to drive the LED pretty hard to get the average current up to 20 mA. If the effective voltage is only 0.25 volts, then the resistor should be 13 ohms, and the peak current will be 120 mA. Can the LED stand a peak of 120 mA? Probably not.

One possible solution is two LEDs in reverse-parallel, that is, one polarized to light during the positive half of the cycle, and the other polarized to light during the negative half. Right off the bat, this doubles the light output, since we're now using both halves"" alt align="right" width="234" height="207">f the cycle. Furthermore, since the only reverse voltage each LED will see is the forward voltage drop of the other LED, you can drive them with just about any voltage you want, so the "duty cycle" can approach 64% pretty closely. Using square-wave AC instead of sine-wave AC would let you reach almost 100%, either by using two reverse-parallel LEDs, or using one LED driven at twice the normal current for half the cycle.

Ok thats all that I can recall that could be useful information off the top of my head.

Questions, comments?


http://flowerforcerled.blogspot.com/200 ... light.html

The significance of green LED light to growing plants indoors
10:43 PM Edit This Green LED light is safe to use around plants at night. The significance of green light to indoor growing operations is not entirely understood. Many people believe that green light is unnecessary to the growth of plants. You will have to decide for yourself, but here's a few quotes and links to get you started.

Plant Development vs. Spectrum by Hurley Shepherd, Agricultural Research, USDA Southern Regional Center

Light is very important to plants since that is the source of their energy. Therefore, they must maximize their use of this valuable resource. The chlorophylls are the energy trapping molecules and use light in the blue and red regions of the spectrum (the green is reflected which is why plants usually appear green).

How does a plant get the most out of the red and blue light that is available? Plants have two other pigment systems, one (called "phytochrome")which detects the amount of red light and one (called "cryptochrome")which detects the amount of blue light.

Phytochrome means "plant pigment" and was discovered based on its effects on plant development due to red light. A plant grown in the dark will be tall and spindly, cotyledons not expanded much, and no green color. In the light, it will be shorter, with bigger, green leaves. Red light controls these and other major developmental changes in plants. Some other changes under phytochrome/red light control are germination of seeds and flowering.

Green-light supplementation for enhanced lettuce growth under red- and blue-light-emitting diodes by Kim, H. H., Goins, G. D., Wheeler, R. M., Sager, J. C. of NASA Biological Sciences

The addition of 24% green light (500 to 600 nm) to red and blue LEDs (RGB treatment) enhanced plant (lettuce cv. Waldmann's Green) growth. The RGB plants produced more biomass than the plants grown under the cool-white fluorescent lamps (CWF treatment), a commonly tested light source used as a broad-spectrum control.

Growing Plants with LEDs by Mihaela Lica

Researchers found out that blue and red light is essential for plant growth and, in general, a percentage of 8% blue LEDs and 92% red LEDs, both with the same frequency and relative intensity per LED, are enough for a harmonious evolution. Blue has a smaller influence than red however a percentage between 1% and 20% of blue light can be selected, depending on the plants and their growth requirements. The NASA scientists have tried to create the most cost and energy efficient light sources possible, and this is why they have eliminated from the fixtures other colours normally found in white light. "What we've found basically is that we are able to limit the amount of colour we give to the plants and still have them grow as well as with white light." said the research scientist Greg Goins of Dynamac Corp

AfganBerry wrote:4. Minimal Heat

You cannot burn yourself on LED lighting. This also means that you will not scorch young or tender plants like MH and HPS lighting can. Reduced heat also means less evaporation and less watering.

Unless you're using the smallest possible LED, yes, you can burn yourself. Not from the LED itself but from the electronics that drives the diodes. While at a recent growing expo I was able to feel how much heat these lights put out for myself. You'll see for yourself once you actually fire your LED lights up. I think this is a common myth but it's certainly a myth. I haven't had time to review the whole thread yet but this jumped out at me and I had to comment.

Hi SME, that quote was from a copy that I was posting from other sources. I can not speak 100% for what they were meaning by the choice of words that they used, however I can make a reasonable guess.

As anyone who has ever seen a LED light in action knows, there are heat sinks and cooling fans already built into current LED lights on the market. You can turn on a LED light and go back 15 minutes later with constant use and stick your hand directly under the lights and not be burnt by the actual lighting.

If you were to however place your hand over the cooling fans for an extended period of time I am sure you will not only burn your hand to some degree, but you also run the risk of doing damage to your LED lighting system. As we all know, heat rises. Since the cooling fans built into LED's are never in the direction of the plants, I assume that the OP was refering strictly to the actual side of of the LED lighting which actually emits the light.

I also believe that the OP was refering to scorching of the plants, not as in nuet burn, but as in actual burning of the plants from being too close to the light source. Everyone who has used HID lighting knows that if you have your plants too close to the light (HID lights, HPS and MH) you run the risk of scorching your plants. When using LED's you do not have this same concern as even though LED's do emit heat it is not in the direction of the plants with normal useage.

Even in consealed spaces, there are ways to allow the heat to escape from your growing area. The heating caused by LED is IMHO far less compared to HID lighting (without any addition cooling method, what I mean is running a LED light with built in cooling compared to a HID ballast and HPS bulb). Yes you can get additional cooling for HID lighting, you have many options to choose from such as air cooling or water for example, however these are not built in methods of the light source, rather they are additions to it.

The whole reason why these types of soultions have been created was because there was a need for it due to the very real problem with that choice and style of lighting system.

I believe that is the point that the OP was trying to express.

I have been around many types of LED lights in action, I have personally seen the amounts of heat that the fans give off. Many local grow stores have atleast one LED light in action and are growing some type of plant to show how well the light can work.

I know you were just quoting a source and I can't say exactly what they meant either but it did say "you can't burn yourself on LED lighting" which is not true. Touch the metal housing/hood and you can and/or will burn yourself. Even the glass, below, on higher powered LED lights gets pretty hot but I don't think people suggest lowering lights that low anyway.

After going over the rest of the thread there's really only a few things I take issue with. The heat myth, energy savings and the overstated grow areas that many "sources" claim. It's sad that so many people will believe anything they read. It's sometimes hard to know what's accurate and what isn't.

The "littlegreenhouse" link, for example, grow area claims are NOT for growing medical crops but might be fine for store lighting or something other crop. We've discussed other manufacturers' claims that are also overstated.

As for claimed energy savings, that assumes that a smaller LED light will cover the same area and/or produce the same or better results, in a smaller area, as compared to a HID and I'm not convinced of that either. I see the prosource claim that they're the "only company that can back up its claims for large-scale production." and I find that claim hard to believe too.

Of course there is also the price of LED which we've been discussing in the other thread.


Other than those things, I'd agree that there in some useful information there. Especially the "coverage" section of one post that backs up my concerns regarding the claims by the people who make LEDs and from the post where they talk about canopy penetration. "When talking about high-quality diodes, it is a difference of up to 4 to 1 in penetration. In other words, if an LED light using a 1w diode can penetrate 4 inches of canopy, then a 3w should be able to penetrate at least 16 inches into the canopy." A big HID can go much deeper.

Yeah I know exactly what you mean. I find it frustrating when companies use misleading and boarderline lying tactics in order to sell their products, rather then being honest and truthful about their products. There are too many companies out there that do this sort of thing. Like HydroGrowLED for example.

With regards to the normal hight useage for LED's I have found that most companies suggest that 12-18 inches above blooming, 18-24 inches above veg plants, and 24-36 above seedlings and clones.

I have placed my hand under led lights that were running for hours at a time and had no issue of burning myself. The cooling fans were rather warm but nothing alarming there either. Lets put it this way, I would much rather stick my hand under a LED light for extended period of time compared to a HPS bulb and ballest.

The heat is not a myth it is just a fact.

The coverage issue all depends on your set up and growing style. What the important factors really are when considering light intensity are the total output of the light source and how it is dispersed over the area. When it comes to LED's, one thing that has a huge impact on coverage is the angle of the LED lenses.

When you have a LED light which is using a 120 degree lens compared to a 90 degree lens, that is upwards of 2x less intensity then the 90 degree lens trying to cover the same area. The further away from the light source the less intense it becomes.

Let me know specifically which questions you have SME with regards to coverage and lighting and I will do my best to answer them for you.

I agree, much-too-much marketing hype and far too little real world reality.

Yes, and I have to dispute the height suggestions as much as I doubt the area coverage claims. I keep my 1000w HPS lights closer than 12"-18" from the top of the canopy, while flowering, and that's without water cooling. Water cooled HPS can be just an inch or two from the tops. LED should be able to get much closer but that would reduce the area covered according to their "claims" too.

The "hand test" is a common way to determine how close you can get a HID light from the plants. You put your hand under the light, at canopy level, and if it's too hot to leave there you move the light up. Again, I think the suggested LED light distance is often overstated to make the area coverage larger.

The myth that LEDs produce "no heat" or that you can't "burn yourself" is a myth. Sure they clearly produce "less heat than uncooled HID" but I'm not sure they produce less heat than a properly cooled HID and it's not that hard nor very expensive to air cool a HID. Water cooling can be expensive, depending on a number of factors, but it's not always needed either. I think air-cooling is enough.

Indeed there are factors to consider but, with HID, the general rule is 50w/sqf or more for quality results. If you stick to that rule it really doesn't effect coverage much. One of the admins here, who has more LED experience than I do, said that he prefers 40w/sqf for LED. If 40w/sqf LED can keep up with 50w/sqf HID, then eventually you could see a ROI but that's where "other factors" come in, not in coverage but in grow style. One example is trees vs SOG. LED on SOG may be fine but for trees you'd want the HID due to penetration differences.

I don't have any coverage questions, I just doubt the claims by most LED manufacturers. There is no way a 600w LED is going to cover the same area as a 1000w HPS and get the same results. In fact, I doubt that a 1000w LED could keep up with a 1000w HPS, in area and results but only an equal test would tell for sure.