Attempt to capture sprectrums of LEDs

RE: Attempt to capture sprectrums of LEDs

DAB — Sat, 22 Aug 2015 19:23:10 GMT

Great post John.

The color LED's are usually created with one specific output band with a little output in other areas.

When you combine LEDs you get mixing as the wavelengths interact with each other in front of your sensor to give you the appearance of more spectral spread.

For growing plants, the mixing is usually enough to permit the plants from pulling in the light they prefer for photosynthesis.

As others have stated, each plant likes specific wavelengths and just about all of them reflect green.

Most absorb deep red and infrared to fuel their growth.

DAB

RE: Attempt to capture sprectrums of LEDs

shabaz — Sat, 22 Aug 2015 15:03:28 GMT

I'm impressed it was able to resolve the amber and green LEDs to quite some detail - more than the datasheet reveals I bet. And examination of your camera image would probably help with intensity measurements for example.

By the way, the second-to-last photo looks like you're trying to create evidence of new UFO sightings!

RE: Attempt to capture sprectrums of LEDs

jw0752 — Sat, 22 Aug 2015 14:44:06 GMT

Thanks Enrico, Shane and Shabaz,

After closing the experiment last night and going to bed I lay in the dark staring at the ceiling and had some realizations. First : The colored plastic of the LEDs I was measuring served as filter material and would have attenuated some frequencies much as a band pass filter does in electronics. Second: The spectrums that were photographed on the diffraction grating were uncollimated and as such produced the spectrum with very wide color bands. Sampling light from a point source would have been much better but the limitations of the sensitivity of my camera and the brightness to which I could push the LEDs were barriers to getting good images. I have renewed respect for the scientists who work with spectroscopy and the precision of their measurements that allow then to make good determinations about the composition of light sources.

John

RE: Attempt to capture sprectrums of LEDs

shabaz — Sat, 22 Aug 2015 14:10:14 GMT

Hi John,

Wow - this is a really great experiment, and still provides valuable information.

Also it shows that sometimes we should try to explore to this level, so that we understand components better.

I think the diffraction grating output is pretty good too, considering that anything more needs quite complex hardware, like a smaller entry and collimation.

As you know, this all gets difficult and time consuming! It is impressive you managed as much as you did in the time you had.

I tried to create a spectrometer at one stage (and selected a grating, mirrors, CCD, etc) but it has been put on hold indefinitely due to all these difficulties.

Even the software to model it all is difficult to use, the trial versions were restricted to very few optic elements, and required background knowledge to use which I didn't have - and apparently neither do eye opticians : (

There are some open source spectrometer projects, but none seemed at a stage ideal to follow. There is a book (I can dig out the title sometime) which had more prescriptive maths and practical guidelines, rather

than a deep physics textbook style, and I followed that at the time. Most of the amateur astronomy folk are interested in this area, so that is a source of useful, practical information.

RE: Attempt to capture sprectrums of LEDs

balearicdynamics — Sat, 22 Aug 2015 06:54:52 GMT

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 [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-27287d92-899d-4ad0-95ea-e822da06abdc/contentimage_5F00_1.png:16:16] 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