It is pretty easy to find the spectra of LEDs online.
For example here
Ocean Optics
I was going to keep my yap shut on this thread because I am not much of a digital photographer yet. But another interest of mine is gemological spectroscopy and gemology generally.
When looking through a stereo scope at a gem whether a diamond or colored stone, the metamerism color shifts of LED light sources is totally unacceptable.
This is in spite of the fact that various sources are starting to furnish them on gemological scopes. THis because they are new, cheap, free from heat relative to quartz halogen, efficient, relatively lower current devices. A lot going for them in fact. But not enough.
And also in spite of the fact that the previously most reasonably priced source of standardized light for these examinations is/was the socalled Daylight 5,000K fluorescent tube. There are many varieties of these each with a different color profile, color rendition index and spectrum. Not surprising because each company manufacturing has their own blend of phosphors that they call Daylight.
Pretty long ago (1989)a two part article was published on this subject which I think I already posted but will post again:
Part One
Part Two
I like this article because it mirrors my own prejudices and states them better than I could ever hope to. Of course when it was written there were
no white LEDs
Spectra for some Fluorescents as well as some rather prickly but well founded opining on the subject of gemological lighting can be found here:
At Adamas Gem Lab
the proprietor Martin Haske does not suffer fools nor BS gladly. He posts some pictures of various fluorescent lights.
When I thought to post on this I thought , well Charles has said exactly what I wanted to say so there is no reason to be redundant. But OK I will be. LEDs are not ready for prime time if you want accurate color rendition.
Similar problems exist for Metal Halide arc lamps which are widely sold to photographers now. They also have rather peaky spectra.
I don't know enough about RGB color and RAW and all that good stuff to know whether a correction can be made for such peaks properly. I suspect a skilled person can. I leave that lecture to someone else.
It is fairly easy to make your own hand spectroscope out of a broken CD and a cereal box. There are also lots of them for sale on ebay starting at about $4.00 for educational ones. You want one with a diffraction grating rather than a prism for the most part. The grating you showed is exhibiting mirror image spectra not spectra according to the scale printed on the slide holder. You need a slit (two razor blades) and a lens and an ocular or your digicam. It is possible to view crude spectra using a digicam but a black and white sensor is better because it eliminates all the Bayer pattern arithmetic after which I would not trust any spectral readout much. But you can get a nice histogram spectrum from photoshop and similar programs.
Here is the website of my friend and spectroscopy fanatic Ioannis Galidakis in Athens.
http://ioannis.virtualcomposer2000.com/ ... index.html
He is also a light source aficionado. Isn't the internet wonderful where people with the most arcane of interests can find each other. (I sent him the Xenon XBO short arc lamp he shows on the website.) He has instructions and analysis (He is a mathematician among other things) of the cereal box spectroscope and others including a monster one he built himself. Great website. Most of the spectra he shows were taken with a digital camera. I don't think he has started on LEDs yet. His links page has everything you could ever want to know about lighting and spectroscopy including some links to pages I wrote most of. (Thank you Ioannis

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