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Re: Microvision's VRD

"Ronald W. Garrison" wrote:
> 
> Blair P. Houghton <bph@primenet.com> wrote in article
> <74kmij$qj8$1@nnrp03.primenet.com>...
> > <angus2@my-dejanews.com> wrote:
> > >they did have a product, I think that most users (even those in the
> > >wearable community) would have significant problems with the idea of
> having a
> > >laser constantly bombarding the retina with focused photons.
> >
> > I don't see why that's a problem, unless there's some way the
> > laser can be made to emit too many photons.
> >
> > I mean, your own eye focusses ordinary photons on your retina
> > at the same intensities.  It just doesn't do it a pixel at a
> > time.
> >
> 
> Actually, I have a nagging doubt of my own, and I haven't seen it discussed
> anywhere. As the laser scans over its raster pattern, it illuminates one
> tiny spot, then another, then another, and so on until it has scanned
> through the entire raster. For a 1000x1000 image, the amount of time that
> the laser spends on any single spot should be something like one
> *millionth* of the total time. This means that the intensity of the light
> at any point on your retina will have a *very* high peak-to-average ratio.
> So although your conscious perception may be that the brightness is not
> that high, any given receptor in your retina will get hit with some pretty
> energetic, though brief, pulses of light.
> 
> The maximum firing frequencies of neurons tend to be on the order of a
> millisecond or so. If you were scanning the raster at, say, 50,000 times
> per second, you could expect the eye to pretty much average things out. But
> if we're talking the usual figure of maybe 50-100 x per second, I could see
> some chance of problems of the type I've described. Maybe not even outright
> eye damage, but perhaps excessive vision fatigue.

I'm not sure I agree with this; light sensation in the retina is the result of a
chemical reaction in the retinal ganglion cells which takes about 25ms to
complete.  It's likely that short bright bursts of light like those created with
the VRD will be no different then a continuous stream of light of a lower level
of intesity.  I think if a crt monitor has no ill effects (since it too scans at
approximately the same rate 50-100x/sec (although I guess you could argue the
phosphor on the display smooths the burst of light out)) that the VRD will also
be safe.

-Paul