Facts & Theory

Subject:	Root development
	Here you can see the huge influence of the different Led colors on plant development, including the roots. FL is fluorecent tube, R = Red, B = Blue and Fr is FarRed. This picture is about Chrysanteums, but I think the reponse of Marijuana will be similair.

Subject:

Evaluating thermal design of a Led panel

One of the most important qualities of Led panels is their thermal design, the junction temperature of the Leds determines the relative efficiency. The lower the temperature, the better it is. There is a very simple and effective way to determine if your Led panel is thermally ok; take a simple light meter and measure the amount of light at the first moment after switching the panel on. Now wait and see what happens while the panel heats up, you'll notice the amount of light drops quite a bit. About 10% drop in light output is unavoidable and ok. However, if the heateffects cause the light output to drop by 20% or more, it's time rethink the thermal circumstances. Maybe adding a tiny high efficient fan is a good idea, but make sure you check it's power consumption first.

Subject:

Popular LedMyths

LEDs are more efficient than HPS. Is not true! LEDs are currently less efficient than HPS, especially the blue ones and they are many times more expensive. A typical HPS gives about 140 Lumen/Watt, where the best LEDs still are at 100 Lumen/Watt. The often-heard statement that LEDs produce less heat than normal assimilation lighting is a misconception. Because the energy conversion is worse than in HPS, the heat per watt still higher than that of HPS. It begins to approach each other but just for the red LEDs and white LEDs. The heat is better to handle because it does not come out the front as radiation, but is concentrated on the back of the chip and can be lead to proper heatsinks. LEDs are more efficient because more light at the most efficient parts of the spectrum is used. Is not true! All photons in the visible light are used at almost the same efficiency. There is a slight decrease for the green photons, but it is no way as bad as Led-panel salesmen would like you to believe. (For fun you can compare this official graph with the ones found on Led-panel sites) Here is the light-output of a typical HPS bulb: As you can see it matches the optimal spectrum quite nicely, using LEDs will not improve this very much. HPS's are really very good lights. LEDs are succesfully used in special horticultural applications but not (yet) to replace horticultural lamps, it will probably take 5-10 years until they do. LEDs have to be placed within a few cm of the plants. Is not true! Light does not lose noticable strengh while travelling, but you have to make sure it is focused properly. Most LEDs have an angle of 120 degrees, you can use lenses or reflectors to make a more narrow beam. Lenses create lightlosses of at least 15%, reflectors only effect the light that is send to the sides and are therefore better. Some people think LED-light has less "penetrating power", which would be another reason to put the LEDs as closely as possible to the plants. Light = light, the penetrating power of a Red photon produced by HPS will be the same as that produced by a LED.

Subject:

Led Facts

The light efficiency produced by a LED depends highly on the working temparature, keep the temperature as low as possible by using adequate heatsinks. Recommended is a temperature lower than 30 degrees Celsius, 86 F. The light efficiency produced by a LED depends highly on the current, using the LEDs at maximum current can reduce the efficiency dramatically, this depends highly on the model of the LED, the small Rebel Leds I'm using have a whopping 40% better efficiency at 350 mA than at 700 mA. For the K2's this difference is about 14%. Led specifications are usually presented to look great. Tricks like measuring the amount of Lumen at a given current and temperature, during only a fraction of a second ( = no heat effects) are widely used. LEDs have an exceptionally long life (40,000 hours) and they are very resistant to bumps and vibrations. Both life and light output are negatively affected by higher temperature. LEDs are available with different emission spectra, which make it possible for processes to send light of different wavelengths. You can control the shape of the plants by using different mixtures of Red/Far-Red and Blue, for both the vegetative and flowering stage. See the document about Light Color below. With LEDs it is easy to control the light and get it where you want it. You can get all kinds of lenses, just remember you lose at least 15% light because it passes a plastic or glass object. LEDs are safe since they contain no glass and operate at a low voltage. The intensity of LEDs can easily be controlled with dimmers. LEDs are small and manageable, this enables them to be placed in rows at the bottom or sides of the plants, or to create 2 rooms on top of each other. LEDs radiate almost no heat to the front, therefore the distance from the plants may be very short. The impact to the environment outside the greenhouse can be significantly reduced, which is an important environmental aspect.

Subject:

Checking out the UFO

Got the UFO today, I bought it at www.ledlightsorient.com, including shipping it cost me 180,- Euro, about 250 U$. It is a 90 watt LGL0505, it looks like a well developed product, on the inside it is build reasonably rigid. The packaging is ok, and the email response from the supplier is very good. Lets have a look at the claims that are made by the supplier: Benefits of our LED grow lights are as follow: 95% energy of LEDs can be absorbed by plants, but only 10% by HPS or MHS. This is a damn lie. It saves 70% to 90% in energy consumption compared to fluorescent tubes, HPS or MHS. This is another damn lie. Totally 90 pieces of 1 Watt Led produce 3800 Lumen. Hmm, I do not think so, I measured the amount of Lux coming out of the 90 Watt UFO and it is definitely less than the present 60 Watt system I'm using for Set-up 6, which puts out about 2100 Lumen while in flowering position. (18 * 85 + 12 * 38 = 1986 Lumen for vegging) Low heat generation. Reduce grow room temperature 15 degrees compare to HPS or MHS. Not if you want to have the same amount of light for your plants, then you will have to fill your room with UFO's, probably generating about twice as much heat as with your old HPS's. Nearly no maintaining. Maybe, but I wonder if the cooling fans will last very long. High power LED estimate to last 50,000 hours. Yes, but the light output will be reduced to about 70% towards the end of the lifetime. Conclusion: Considering the low price it is a rather good product, maybe the best Ledgrow system on the market today. But it is a shame that the huge claims and promises; "replaces a 400 Watt HPS" are a pack of damn lies. Just as with all other Ledgrow products out there.

Usefull documents:

About HPS lights

About lightcolor for plants

Usefull links: