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  • Author Author: jw0752
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Attempt to capture sprectrums of LEDs

jw0752

Earlier today in a blog post  http://www.element14.com/community/community/design-challenges/vertical-farming/blog/2015/08/16/use-of-leds-in-vertical-farming

I volunteered to try to capture the spectrums of some of the common LEDs. The discussion in that thread had been about the effectiveness of LEDs as grow lights for the Vertical Farming Challenge. I have a cheap spectroscope that I got to show the grandkids about how we can know the elemental composition of things by looking at their spectra. The poor quality of my results made me decide to present the pictures as a separate Blog so that I wouldn't mess up the other discussion . I have reference the other discussion above and I will cross reference this one in that thread.

 

There were a couple strikes against me from the start as the spectroscope was cheap and my camera was never designed to take pictures in a spectroscope.

Here is a picture of the bright line spectrum of a fluorescent light taking after 20 picture and 2 hours of experiments.

 

image

 

Notice the bright green line at 546 nm. This line is from the Mercury in the fluorescent tube. My hope was to get images like this of the light from different color LEDs but that wasn't to be.

 

I fell back on plan "B" and used a diffraction grating in front of the different color LEDS and photographed the spectrums created on the grating.

 

Here is a picture of the spectrum  of a RED LED. In this case I could see no spread outside the Red in the spectrum.

 

 

image

 

I next chose an Amber colored LED and this time we get a few colors in our spectrum.

 

 

image

 

 

Moving on to the Green LED we also see a fairly good spread of color in the spectrum.

 

 

image

 

 

The Blue LED had some spread to the longer wave lengths that I could see with my eye but the camera had difficulty capturing them.

 

 

image

 

 

Finally I took a picture of a white light LED and got the best spectrum, as we might have expected.

 

 

image

 

Other than a curiosity this information will be of little help in the Vertical Farm Project. I was surprised that the LEDs that I tried had as much spectral spread as they did. I really expected a much narrower band of light.

 

John

  • in reply to balearicdynamics

    Great post John the information is great I'm surprised at how much of the spectrum the LEDs capture

  • Hello John, very well done test. No matter the images but it's important to give the idea and your written text.

     

    I was surprised that the LEDs that I tried had as much spectral spread as they did. I really expected a much narrower band of light.

     

    I think that this is the opposite, instead image As LEDs are not - I don't expect this - a perfect monochromatic light source it sounds me normal that while the predominant light is the one we expect (red, blue etc.) but there are impurities that makes a wider spectrum, probably impossible or very difficult to perceive with the naked eye.

    About the amber LEDs I have the suspect that their generates a sort of compound light from a mix of the original LED source and the plastic filter of the LED caps. Is this possible?

     

    It will be interesting - just an academic disquisition - to see how much "pure" is the led light generated by the the low power lasers in the DVD and Blue-Ray readers.

    It will be also interesting a comparison between your results, underlined by the experimental evidence and the spectral response as declared by the producer o the datasheet.

     

    Enrico