----- Original Message -----
From: "Jon Baker" <jon@HAYSEED.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, January 16, 2002 10:02 AM
Subject: [ee]: photodetectors ( tag changed from OT)


> I am working on a similar but slightly more complex project at the moment
> which needs to detect 4 different wavelengths of light emitted from a
sample
> luminescing. The amplitude ( brightness??) of the light at each frequency
> must be measured independently so I can draw 4 graphs- each frequency
> corresponds to a particular molecule and the graph is to show the
> concentrations ( brightness ) with time of each. I am positive this can't
be
> done with filters over photo detecetors becuase the number of photons I
need
> to detect is so small it would be absorbed into the filter. What would be
> ideal is a several photodetectors each of which is sensitive to a
> (different) narrow band of wavelengths. Does anyone have any pointers
where
> I could look for such specific devices?

I have heard and theoretically it should be true that LEDs work 'backwards'
as well...as photodiodes. You 'just' need to amplify and measure the output
current of different coloured LEDs. But it may not be anywhere near the
sensitivity needed, I've never tried it.
/\/\/\/*=Martin

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