new Led lights

[terryros]

Let's take as an example the MR16 Cree 7W-38 degree Natural White bulb. If you want to look at the specs yourself, here is a link:

http://www.orchidweb.com/altpdf/alt_mr16.pdf

The dominant wavelength of the Natural White has a minimum of 3500K, a typical of 4100K, and a maximum of 4500K. Color temperature is directly related to wavelength and if you use the formula to convert to nanometers you get 828, 707, and 644, which nicely covers one of the two main peaks of chlorophyll a.

What I like additionally about the Natural White is that colors of plants and flowers look very natural in color.

If you look at the spec sheet, at 0.5 meters distance, the MR16 7w bulb is producing 6148 lux, which is 571 footcandles. You can use some math to figure out the lux/fc at any distance from the bulb as well as the size of the circle of light created by the 38 degree bulb. That is how I determined that at 30 inches height you get a circle with a diameter of 21 inches with 246 footcandles. If you overlap bulb coverage, the overlap zones have approximately double this intensity. I chose 21 inches because that is the functional width of the humidity trays that I grow everything on.

I think that many experts think that even 250 fc of the right kind of light for 14 hours or so is enough light to grow most Phal, Paph, and Phrags. With the correct bulbs at the correct height and with appropriate overlapping it is easy to have growing zones of 500-750 fc which should be sufficient for many medium and higher light requiring types.

The initial downside to these lights is their initial cost - they are expensive. It is only when you take the longer term view of electricity expense and replacement costs of other lights that you can see yourself breaking even or getting ahead several years out.

Less electricity, less heat, greater bulb height over high-spiking plants, less replacement of bulbs, and a spectrum well suited for photosynthesis were my motivations to switch.

[Connie Star]

Originally Posted by ericst11

Here are the facts on induction lighting.
http://www.warehouse-lighting.com/pd...son%5B1%5D.pdf

Here is also a good artical on LED's and it compares most lights and led's read and see if they are really worth the money.
Myths Busted, LED Lighting

Is induction lighting synonymous with LED?
I have bought a couple of smaller LED lights that I've got shining on my plants along with T5s, which is not going to tell me much. Please keep us posted on how this goes.
Do you mind telling how much your set-up cost?

[terryros]

The BR30 bulbs cost $100 a piece and the MR16 bulbs cost $70. So, it looks like I have spent about $1,900 so far on lights. I eventually need another 6 BR30-type lights but have enough room to grow right now so I can wait a bit. On electricity costs alone it takes many years to get back to even, but if you figure in having to replace fluorescent tubes periodically, the break even point comes much sooner.

[calvin_orchidL]

Connie - induction has nothing to do with LEDs - it is similar to fluorescent tube lighting except there are certain differences in the way that the gas is excited that reduces heat and improves efficiency.

terryros - the sun is at a colour temperature of 6500K...are you sure you're covering everything?
If you look at PAR (photosynthetically active radiation), there are absorption peaks at 400-500nm as well. I'd like to actually see spectral charts of the orchidweb LEDS.

Btw if you're interested, the cree XP-G LEDs (datasheet here) have emission spectra that are quite decent, also white light (not those horrible blue/red combos), if you ever want to make your own arrays. I know you've invested in these orchidweb lamps already, but if you are hoping to expand, this might be more economical.

[Ray]

The color temperature of a phosphor-type LED varies a bit with the applied current, but many are rated in the 6500°K area, which replicates most-closely the incoming light of a clear summer day, made up of direct sunlight and atmospheric reflection from the blue sky.

You might get a kick out of this: Light Sources & Color Temperature

[monna lisa]

Thanks for your very interesting comments.
My main doubt is: having this kind of lights a beam angle of 38 degrees, and behaving as spot lights (no diffuse light) how many Led lights would I need to enlight properly an orchid case measuring 1,2 m (height )x 1m (length) x 60 cm (depht), in which Paphios an Phrags are on the ground and the back wall is totally covered by high light requiring mounts?

[terryros]

There really isn't one sun color temperature because it all depends on the time of day, etc. A light that was all 6500K color temperature corresponds to a 446 nm wavelength, which is in the blue part of the light spectrum. Such a light would be bluish. This wavelength covers the first peak in chlorophyll a and b absorption but not the second. There are some experts who talk about this part of the spectrum being important for vegetative growth while the second chlorophyll peak absorption peak in the redder part of the spectrum (color temperature 4400 to 4000k, 640-680 nm) is important for flowering.

Chlorophyll appears to have two types and each type has two separate peaks all in an attempt to be able to photosynthesize under a variety of light conditions, which makes sense as seasons and time of day change for plants. What we need to know is whether both chlorophyll a and b and both of their peaks need to be saturated for optimal growth or whether only supplying optimal saturation in one of the chlorophyll a peaks is sufficient to maximize photosynthesis.

Since the Natural White LED lights I am using do not appear red, we know that although they may have a dominant wavelength in the redder part of the spectrum, they also have some spectrum in the shorter wavelengths.

In any growth situation, you have to consider how much head room above the plants you need, the coverage area required, the footcandles/lux that you need, heat considerations, and electricity cost to figure out what to do. In the box described by monna lisa, I don't think one set of LED lights would work because you are trying to illuminate a base 1.2 m away as well as the vertical wall itself. I think those are two different surfaces. Two different tracks might work (one for the base and one for the wall) but it sounds tricky. The 120 degree dispersal angel LED lights can cover a 1 m diameter circle from a height of about 11 inches, but only with about 210 fc illumination. As you decrease the height, the coverage circle decreases and the light intensity increases. You have to figure out the balance that you need. I have a spreadsheet that I prepared that shows the light intensity and coverage circle diameter for any particular height with the three types of bulbs that I am using.

[Ray]

My understanding of color temperature is that is does not correspond to a single wavelength at all, but is a way to describe the relative ratios of all of the colors in the spectrum.

At lower "electron excitement levels" (temperatures), electrons are are only moderately "bumped" up in energy, so when they fall back, they emit longer, lower-energy light (toward the red end of the spectrum). Excite those electrons more, and they can climb to even higher levels, and when they fall back, they emit higher energy, shorter-wavelength length, moving more and more toward the blue end as the energy input increases. The lower-energy species are still there, so the emitted light becomes a mixture of wavelengths. If they didn't, we'd see a clear, incandescent bulb on a dimmer go from red to blue as the energy increased, not red to white - a mixture of colors.

At about 5800°K, the intensity of the light in the red and blue regions that span the chlorophyll absorption areas are about equal. At 6500°, the blue is slightly greater (the spectra are from a tool that uses the Stefan-Boltzmann Law to predict the spectrum of black-body radiation; the lines are mine, to demonstrate the difference - they are probably not placed exactly correctly):

From what I've read (which, of course could be incorrect) that 6500° spectrum corresponds more closely to the relative rates of chlorophyll absorption, i.e., the blue is absorbed slightly more than the red.

Another factor to keep in mind that in order for a bulb to emit light at a higher color temperature, more energy needs to be applied, which also means more energy will be emitted. In fact, at 6500°K, the energy intensity is close to 3x what it is at 5800°K, which suggests to me that a higher-temperature light source that still provides a decent red/blue balance gives you more bang for the buck.

[terryros]

I would agree that the expressed color temperature of a light is really the dominant wavelength and not the only wavelength. I got my calculations for the translation of color temperature in K to wavelength in nm from this post regarding growing what I think are mushrooms! Below is the link:

Relationship between color temperature, wavelength, and CF light - Mushroom Cultivation - Shroomery Message Board

It looks to me like a specific color temperature does translate to a specific wavelength, but that no light source (?maybe a laser) emits just that wavelength. So, the LED lights I have been talking about cite a "dominant" wavelength range, which means that there are other wavelengths being emitted in lesser amounts.

My reading finds that chlorophyll b is an auxiliary chlorophyll, transferring its energy to chlorophyll a to do the actual photosynthesis. However, the relative importance of chlorophyll absorption in the shorter wavelength, bluer 400-470 nm (7244-6101K) part of the spectrum compared to the redder 625-675 nm (4636-4293K) part of the spectrum I have not been able to figure out. Maybe we don't know for orchids and I will just have to find by getting poor growth with these lights. That is why it is an experiment.

[littlefrog]

Photosynthesis is much more efficient if you start at photosystem II (I think that is Chlorophyll B, whichever one absorbs at 680nm). Between photosystem II and I (yes, II is first, it kills my students) there is an electron transport chain that will result in the generation of significant amounts of ATP. The 'leftover energy' is passed to Photosystem I (+more photons) which goes through the other chlorophyll which absorbs at 700nm. This kicks the electrons up to the point where you can reduce NADP+ to NADPH.

You need both ATP and NADPH in the calvin cycle (dark reactions) to make sugars. ATP is generated by photosystem I in the absence of photosystem II, but I would bet good money that the best option is to supply both 680 and 700nm for optimal results. Of course other wavelengths are necessary for proper growth and flowering, too.

I'm interested in these new LEDs, I might have to try them soon.