LED Grow Light Spectral Output / Testing LEDs

14. November 2012 by Mike in Spectrometer  //  Tags:   //   Comments (0)

I'm currently tweaking the spectral output of my grow light using an ASEQ LR1 USB Spectrometer. The Spectrometer is a really nice piece of kit, it is powered from the USB port so no external adapter needed. The software is small and very easy to use.

 In the image you can also see the fibre optic cable (orange) which guides the light to the sensor. It is extremely directional so as long as you test in a dark room then its easy to filter out ambient light.

 

Spectral Output (3W (Double diode) Cool White LED)

 

Spectral Output (3W (Double diode) 660nm Red LED, 3W (Double diode) 630nm Red LED)

 

Current combined output with both white and red LED channels at 100% output. This would be ideal for the flowering stage of the plant as there is adequate output in the 500-600nm region for non-photosynthesis processes.

I now need to work on the correct light mixes for the other stages of development.

Here is the salad crop (Rocket & Spinach) I'm testing with at the moment. There is a very good chance it won't grow properly as the wavelengths are far from optimal for vegetative growth.

DIY LED Grow Light

14. November 2012 by Mike in LED Grow Light  //  Tags:   //   Comments (0)

I'm currently experimenting with growing plants with LEDs.

LEDs have a number of potential advantages for growing :-

  • Indoor growing as no natural light required. This obviously means its easier to keep insects and bacteria/mold that might damage the plants
  • Targeted light spectrum for various stages of plant development
  • Very efficient with low electricity usage
  • Low heat output relative to light when compared to other artificial light sources
  • When combined with hydroponics very fast growth can be achieved

The ability to grow all year round is especially interesting to me living in the UK as we don't have the best weather. I've had very mixed results growing outside in our climate, a few times the strange weather patterns have stunted the growth and caused plants to flower early etc.

DIY LED Grow Light

Drilled Aluminium plate, with two 120mm fans mounted on spacers. Cooling is reversed (i.e air blown upwards for maximum efficiency). LED Drivers not show. The holes visible on this side of the plate were to route the wires from each PCB but I foolishly put them the wrong side on the design - duh!

This light features 24x3W cool white LED's and 24xRed mix (660nm,630nm) with 60 degree emitters. I had to have the LED's manufactured in China as most come with 120 degree or higher emitters which aren't suitable for plant growth (The LEDs in the image are actually 120 degree ones, the 60 degree ones are on another light).
The PCB's are custom designed with aluminium backs. They are held flush to the heat sink with a series of bolts and washers (3 each side). Temperature regulation is extremely good, less than 10c rise above ambient temperature.

The spectral output is no where near correct yet. I'm working on that at the moment!

60 degree on the left, 120 degree on the right. It is better to have the lens as close as possible to the LED to avoid losses. Some people put 60 degree lenses in front of a standard 120 degree LED but that just results in further loss of light.

 

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