Efficiency 660nm GaAlAs LEDs

I'm planning to do some experimentation on how plants react on monochromatic light or selected wavelengths. As you probably know, the photosynthesis action spectrum peaks at +/- 450nm and 670 nm. There's also some action around 480 nm from the carotenoids.

My question: does anyone know the pure radiometric efficiency of GaAlAs red LEDs (peak at 660nm)? I know the newer GaAlInP LEDs are way brighter, but I think this is mostly because of the shorter wavelengths (<640nm..brightness is calculated with our own eye response curve in mind )...or do they really put more miliwatts of light?

So should I use GaAlInP LEDs which are brighter but have a less favorable spectrum or should I use the 660nm GaAlAs LEDs?

Thanks!

Efficiency of AlGaAsP is very variable. Most of them are indicator lights, with low efficiency. But there is some with efficiencies over 30% (radiometric optic PAR output/input energy).

The problem is most of current research is in the Ga field (AlInGaP in red), so there is little AlGaAsP improvement expectations.

The main limitation of AlGaAsp is they need to run at low current, most of them are 20mA devices, and some up to 50mA. In order to get enough light for plants, you need to use a lot, or use COB technology.

In my understanding, AlInGap reds led can cover the 660-670nm range perfectly. Manufacturers use the percentage of meterials in order to obtain the max photometric effect, both in orange and red leds, so they choose the 625-640nm range as goal. But if there is enough demand of 660nm high power leds, probably they will do it.

Hope some of the brains here can confirm that.

Using 640nm devices have some advantages, apart of its wide avalaibility. At 640nm, the unbalancing between Phytochromes of red and far red is reduced, thus aporting 730nm light is less critical, at less in short day flowering plants.

In the other hand, 640nm light excites Photosystems I and II in a similar way, allowing them to work at full power, disminishing the effect of lower photosyntetic action of 640nm against 660nm when light density is high.

So i suggest you to try with AlInGaP leds. Some manufacturers, ie Lumileds, have their red leds binned up to 645nm dominant wl, wich correspond to about 660-665nm peak wl, but i asked some of them in the past and they dont have the longer wl binnings avalaible.