Re: UV Hazards and concerns

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Tue, 7 Oct 1997 17:59:29 -0500
>From: P3D Bob MAXIE  <BMAXEY@xxxxxxx>

>Rest a little better in knowing that if the light
>source emitted harmful amounts of UV, the
>CDRH (Center For Devices and Radiological
>Health) would require the manufacturer to
>mark the device as such.

That's a good point. On the other hand, I consider it likely that the ratings
of devices take into account the conditions under which they are likely to
be used. The fact that fluorescent camping lanterns are available without
these warnings indicates that at least they are considered generally safe
when used as camping lanterns - staring into the tube for long periods at
point blank range might (or might not) be a different matter.

Two additional pieces of "evidence" for weighing possible risks:

- Fluorescent backlights are used in many flat panel displays, and I haven't
heard of any UV concerns regarding them. But the backlight lamps differ in
many respects from the camping lantern lamps (high voltage, high frequency,
small diameter, intensely bright), and the light has to get through many layers
of different materials before it gets to the eyes, so the example may not be
entirely relevant.

- When we used to work extensively with ultraviolet erasable EPROM memory
chips (with a transparent window over the chip to allow erasure), the data
sheets noted that the chips would be erased fairly quickly (days or weeks?)
if kept exposed to sunlight, more slowly if exposed to room-level
intensities of fluorescent light (months?), and far more slowly or not at all
if the chip window were covered by an opaque material. From this I would be
inclined to suspect that regular fluorescent lamps put out a relatively small
amount of UV when measured at a distance of several feet. But I don't have
an idea of the relative intensity at different wavelengths.

It has been pointed out earlier that even incandescent lamps (especially
halogen lamps) put out some UV - several people who work with them have
commented that they do not consider the expected exposure when used in a
3D viewer to be a significant risk. 

John R


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