Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site petrus.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!bellcore!petrus!karn
From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.audio
Subject: Re: cleaning cd-player optics
Message-ID: <415@petrus.UUCP>
Date: Sun, 21-Jul-85 23:05:30 EDT
Article-I.D.: petrus.415
Posted: Sun Jul 21 23:05:30 1985
Date-Received: Wed, 24-Jul-85 21:01:03 EDT
References: <412@petrus.UUCP> <4034@alice.UUCP> <414@petrus.UUCP>
Organization: Bell Communications Research, Inc
Lines: 22

Just after posting my last note, I found the following in Reference
Data for Radio Engineers (p 22-5, 1977 printing):

"The lower limits of visual response at the extremities of both the photopic
[cones] and scotopic [rods] are not necessarily restricted to the range
of wavelengths normally defined as visible light. For example, many observers
can see the 905 nm radiation from a GaAs injection laser or the 1.06 micron
radiation from a Nd3:YAG laser if the intensity is sufficiently high.
Fig. 6 is an extension of the absolute scotopic luminosity curve showing
that a GaAs injection laser emitting at 905 nm will elicit a visual response
in the mind of an observer whose eyes are sufficiently sensitive to respond
to ~1e-6 lm/W. --> Since moderately high energy densities at the retina may
be required to elicit visual response at near-infrared wavelengths, the
safety factor must not be discounted." <-- [emphasis mine]

The item was quoted from F. J. Gardner, "Effectiveness of IR Covert
Illuminators," RCA Lasers, 1974, pp. 178-181. From the accompanying table,
it looks like the rods have about 1.39e-7 of the efficiency at 780 nm
that they do at the peak sensitivity of 510 nm (green). This is something
near 70 dB down.

Phil