Aquarium LED fixtures

[terryros]

Although the reduction in electricity costs over time (and less replacement of bulbs) defray some/much of the initial cost of the LED lights for an orchid grower, cost was not the main issue that I converted to all LED lights two years for my indoor orchid growing.

The two things that I wanted, and have achieved, are greater height of the bulbs over the plants and much lower heat production in my enclosed indoor growing area. Each of these has been very important in improving my growing.

Although I previously grew with fluorescent lighting, I will claim no superiority for the LEDs because I have also changed growing media (now NZ sphagnum) and fertilizer (now K-Lite at 50 ppm N). However, what I am growing (Paphs, Phrags, Phals, Miltioniopsis, and some Catts) is growing well and blooming. My LEDs are all from Orchids Limited and are mostly natural white. I target about 500 fc at the top of each plant although I realize this has less meaning with the focused LED lights.


Sent from my iPad using Tapatalk HD

[Ray]

Originally Posted by DavidCampen

LED grow lights are still so expensive per watt compared to MH, HPS or fluorescent that they can't really be cost justified unless you need one of the specific properties of LED lights that the others don't have. LED fixtures will cost you $4-$5/watt whereas you can get T5 fluorescent for less than $1/watt.

That is mostly true David, but prices are coming down and you can't forget the life of the light source.

Bulbs like the "Jungle Dawn" advertised here sometimes run about $3/watt, for example.

Many T5 bulb manufacturers state that their bulbs are good for two years, but I have measured significant light reduction in one. A well-made LED light ought to be good for ten years with no degradation in light quality. Consider replacement cost and LEDs look better.

[DavidCampen]

Originally Posted by Ray

That is mostly true David, but prices are coming down and you can't forget the life of the light source.

Bulbs like the "Jungle Dawn" advertised here sometimes run about $3/watt, for example.

Many T5 bulb manufacturers state that their bulbs are good for two years, but I have measured significant light reduction in one. A well-made LED light ought to be good for ten years with no degradation in light quality. Consider replacement cost and LEDs look better.

$3/watt is a good price that is approaching competiveness with linear fluorescents. For someone who wants to light a terrarium or two the 13 watt Jungle dawn LEDs certainly compete with CFLs.

But for someone needing the equivalent of a 6 bulb, 4 ft. , T5HO linear fluorescent (320 watts) the 13 watt Jungle Dawn are not in the running. It would take about 25 of the Jungle Dawn units at a cost of $1000 to equal the T5 fluorescent fixture that costs $200. Even if you replace the T5 bulbs every year for ten years your cost for bulbs will not be more than $900 (and should be much less if you do a bit of comparison shopping). So the cost of the LED installation vs T5 would not break even for at least 10 years. (And this is also ignoring that the 25 Jungle Dawn units would take more space than a 6bulb, 4ft T5 fixture making the Jungle Dawn not actually practical for this application.)

Also LED light output does degrade over time. In a well designed LED fixture the rate of degradation should be a tenth that of fluorescents but the caveat is that it is easy to build a poorly designed LED fixture where the LEDs will degrade very rapidly. Unlike fluorescent bulbs, LEDs are sensitive to temperature - the LED diode junction will degrade rapidly at elevated temperatures.

[Ray]

Originally Posted by DavidCampen

Each type of LED radiates in a specific narrow wavelength range. Manufacturers of these fixtures should specify the specific wavelength for each type of LED in the fixture not some bogus, useless "color temperature".

Not true, David.

Of the 64 chips in the LEDs I am carrying, only 8 are discrete wavelength types - the red ones. The other 56 are phosphor-type chips that use a blue or UV LED to excite a phosphor into emitting a wide spectrum of light, not a discrete wavelength. Same principle as a fluorescent tube. There are three different chips on the board, and if they were all discrete, the spectrophotographic plot would show three, discrete peaks.



You are correct about the common use of the corrected color temperature. it is intended to discern differences to the eye, not strictly the definition of the spectrum as color temperature was originally derived. However, in high-quality horticultural light sources (designed specifically for plants), the phosphors are combined to replicate the original more closely.

[Magnus A]

Ray,
Usually when people show plant absorption spectrum to show what wavelength is neaded there is a significant valley in green, if any absorption at all. Plants are said to not use green and that this light is wasted energy.

Did you chose this particular spectrum to motivate your fixtures large output in green?

/M

[DavidCampen]

Yes Ray, if the LED fixture uses white LEDs then it has colors other then the LED primary colors. My main point that still stands is that the Color Temperature is meaningless for light sources that deviate significantly from the emission of a Planckian radiator and with an LED fixture claiming a color temperature of 40,000degK (LOL) there is no way of knowing what the people marketing that fixture mean except to guess that they have added a significant proportion of blue (without phosphor) LEDs.

Oh, and the figure you give of a white LED output does show the peak from the underlying blue LED emission.

Again, the extreme so called color temperatures stated by aquarium lighting vendors are basically worthless marketing hype.

[DavidCampen]

Originally Posted by Ray

... You are correct about the common use of the corrected color temperature. it is intended to discern differences to the eye, not strictly the definition of the spectrum as color temperature was originally derived. However, in high-quality horticultural light sources (designed specifically for plants), the phosphors are combined to replicate the original more closely.

To replicate what "original"?

High quality horticultural LED light sources use predominately blue and red LEDs (no phosphor). White LEDs, because of their lesser efficiency, are used only if necessary to assist the humans working with the plants.
Philips GreenPower Horticultural LED Grow Lights

[Ray]

Magnus - it is the chlorophylls that do not absorb the green, but there are other chemicals in the leaf structure that do, some of which pump energy directly into the photosynthesis process. That upper curve is a total absorption of all chemicals - i.e, their individual curves blended.

The "hump" in the LED output is a remnant of the phosphors used to produce white light. It's presence doesn't detract from the absorption (or the appearance, which was the goal), and adds a little, so I'm OK with it.

David - by the "original", I was referring to matching the blackbody spectrum. The don't do so, but come closer to doing so than the cheap bulbs we find at the hardware store.

I'll grant that the white LED light is not a necessary thing for the plants, but if you want to grow and look at your plants in a home environment, they do look a lot better than the red/blue combination. Ignoring that fact is folly.

[DavidCampen]

Originally Posted by Ray

...I'll grant that the white LED light is not a necessary thing for the plants, but if you want to grow and look at your plants in a home environment, they do look a lot better than the red/blue combination. Ignoring that fact is folly.

I quite agree, most people want white light not bluish-red and therein lies the crux of the matter - current technology white LEDs are no more efficient than T8 or T5 linear fluorescents in supplying light for photosynthesis. If you want to reduce electricity use over fluorescents by using LEDs then you need to use mostly deep red LEDs.

[naoki]

Ray is right that there are other pigments in the antenna complex of photosystem 1 and 2. One of them is carotenoid (the primary role of this is more of anti-oxidants). These other pigments transfer the energy via resonance energy transfer, and the energy which have reached to the reaction center (P680 and P700, both chlorophyll a) will be used for the light reaction of photosynthesis.

But I'm wondering if your figure is really an absorption spectrum. I'm not completely sure about the difference between PS quantum yield vs PS action spectrum (which is different from PS absorption spectrum), but it seems to be closer to quantum yield indicated in Fig. 2 of
D.R.Geiger - LIGHTING REQUIREMENTS FOR PHOTOSYNTHESIS