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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Blue and UltraViolet LED's
Summary: LED encapsulent a limiting factor for UV radiation
Message-ID: <3843@kitty.UUCP>
Date: 11 Jul 90 19:56:21 GMT
References: <17596.2699d803@uctvax> <HESKETT.90Jul11122218@mercury.titan.tsd.arlut.utexas.edu>
Organization: Recognition Research Corp., Clarence, NY
Lines: 22

In article <HESKETT.90Jul11122218@mercury.titan.tsd.arlut.utexas.edu>, heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) writes:
> The one I bought from Ledtronics (?) has a color that is a sort of
> 'powder' blue.  The light was bright enough, just not a very intense blue.
> 
> A look at its spectral output curve showed no output in the UV.  I was
> hoping to use it as a sensor in the UV (most LEDs will work as low
> power photoelectric sensors).  I don't have the spec sheet here with
> me, but I believe the 'blue' end cutoff was at about 470nm.

	LED radiation emission technology issues notwithstanding, only
certain special plastic formulations are capable of transmitting UV
radiation without an overwhelming degree of attenuation.   Most LED's
that I am aware of are encapsulated with epoxy materials that have a
usable low end wavelength around 400 nm.  While some plastic formulations
such as methacrylates can be used as low as 275 nm, I am not aware of
any such material being used in LED's, however.

	It is therefore not surprising that you detected no UV radiation.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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