Tito
You didn't mention why you thought you needed a full spectrum for a plate reader.
I would think 8 colors is overkill.
NASA doesn't use more than about 4 or 5 colors for most earth imaging.
You can tell chlorophyll from green paper with RGB and an infrared channel.
Just looking at the levels of R, G, and B gives you 16 million colors on your computer monitor.
With 8 bits of resolution on your A to D converter, and three LEDs, you can easily
split the spectrum into 16 million pieces, which ought to be enough. Sodium
yellow will excite the green and the red LEDs more than the blue one, and you
can get the frequency pretty darn close with 24 bits of data.
The novel use of an LED as both light source and detector for analytical applications has been developed by Lau et al. [74, 75]. The emitter LED is forward biased while the detector LED is reverse biased. Instead of measuring the photocurrent directly as performed by Mims III [82] and Berry [84], a simple timer circuit is used to measure the time taken for the photocurrent generated by the emitter LED to discharge the detector LED from 5 V (logic 1) to 1.7 V (logic 0) to give digital output directly without using an A/D converter or operation amplifier. This method achieves excellent sensitivity in comparison to the method of operating an LED as a photodiode (i.e. to measure directly photocurrent) [81].
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