Check out Hammamatsu.  They make everything from a pin diode to an avalanche
diode.  The prices will range from about (free sample) to $1200.00 USD
----- Original Message -----
From: "dr. Imre Bartfai" <root@PROF.PMMF.HU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, January 04, 2004 10:32 AM
Subject: Re: [EE]: How to measure light? Phototransistor?


> Photoresistor? Wide conductance range depending on light level...
>
> Imre
>
> On Fri, 2 Jan 2004, Edson Brusque wrote:
>
> > Hello everyone,
> >
> >      I'm scratching my head for some days but still haven't found a
> > simple and working solution to measure the light level on a given
ambient.
> >
> >      I've been trying it with this circuit:
> >
> >      +5V
> >       |
> >       C
> >       E(phototransistor)
> >       |
> >       +----ADC(PIC)
> >       |
> >      10k(resistor)
> >       |
> >      GND
> >
> >      But the results haven't been that good. Lots of noise and very poor
> > linearity. Also, I've tried I->E (current->voltage) converters using
> > opamps but still nothing have convinced me.
> >
> >      To easy the implementation simplicity is very desirable. I don't
> > need a precision circuit and I don't need to convert the readings in lux
> > or any other real-word value.
> >
> >      The circuit would be used for feedback on a system that will try to
> > keep the lighting level constant on an ambient with natural and
> > artificial lighting.
> >
> >      Someone been there and done that? Any ideas?
> >
> >      Thank you very much,
> >
> >      Brusque
> > --
> > ---------------------------------------------------------------------
> > Edson Brusque                     C.I.Tronics Lighting Designers Ltda
> > Research and Development                   Blumenau  -  SC  -  Brazil
> > http://www.suporte.ind.br/ryan/netiqueta.htm     www.citronics.com.br
> > ---------------------------------------------------------------------
> >
> > --
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