Don Klipstein
Guest
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 Posted: Sat Oct 11, 2008 5:17 am Post subject: Re: CFLs emit dangerous amounts of UV... |
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In <d3a0255c-cb12-4a3f-af15-938bb1a604a3@h60g2000hsg.googlegroups.com>,
Adam Aglionby wrote:
[quote]Whats green and got nasty a red rash, a CFL SAD lamp user?
http://www.independent.co.uk/life-style/health-and-wellbeing/health-news/
energy-saving-light-bulbs-can-emit-enough-uv-radiation-to-damage-skin-
956696.html
Sounds like one for the CFL FAQ Vic.
[/quote]
That article says, for one thing:
"The research showed that one in five of the "open" bulbs emitted UV light
equivalent to that experienced on "a sunny day in summer" when in very
close proximity (less than one inch) to the skin".
I just took a light meter to 1 inch from a Philips 25 watt SLS "triple
arch". I mostly get 40,000-53,000 lux. As in around 40-50% of noontime
direct sunlight.
And I know darn well for sure that ratios of UVA to photometric content
and UVB to photometric content are well under the corresponding ratios in
sunlight and daylight. Have a look at published spectral power
distributions of midday sunlight, overcast daylight, clear sky, and CFLs
of your choice.
The article also said:
"Open bulbs should not be used where the user is closer than one foot for
more than one hour a day, the agency said. Encapsulated lights with a
double glass envelope did not emit significant amounts of UV light, the
research found, and could be used in place of the open kind for close
work."
Most of the UV getting out of the CFL tubing also gets through a glass
outer bulb, although the trace of UVB will be largely blocked by the outer
bulb.
Also, consider that most of the small amount of UV getting out of any
CFL is 365-366 nm, which has much less effect on skin than an "equal
quantity" of the UVA-portion of daylight and midday sunlight. UVA
includes both suntanning and non-suntanning wavelengths and is 315-400 nm.
UVA effects on skin from sunlight and daylight are mainly from the
minority of daylight/sunlight UVA of shorter-UVA wavelengths in the
315-340 nm range.
The above article also says:
"The problem only occurs when the lights are used for close work, such as
in desk lamps or reading lights. When the light is more than one foot away
there is no danger, the Health Protection Agency (HPA) said."
Keep in mind that desk lamps and reading lights are generally at least a
foot away from you. Desk lamps closer to you than a foot are mostly
illuminating yourself most strongly on regions of your person around or
over a foot away, unless they irridiate your person less than they do
onto anything 1 foot directly ahead.
Later in the article, it says:
"People should not be thinking of removing these energy saving light bulbs
from their homes. If you need to use one closer than one foot away, it>s a
simple adjustment – either move the light or replace it with an
encapsulated bulb. I walked round my own home and found none of my energy
saving bulbs were used closer than one foot. In situations where people
are not likely to be very close to the bulbs for any length of time, all
types of compact fluorescent light bulbs are safe to use."
He dismissed suggestions that close exposure to the UV light emitted by
the bulbs could cause cancer. "That is not what we are saying. At the
exposure levels that we are talking about, the worst is that you could
have short-term reddening of the skin. We do not believe these lights pose
any risk in terms of skin cancer." However, people with light-sensitive
conditions "need to be careful", he added.
So it sounds to me like somewhere between a minor problem and a
non-problem.
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One more thing: People using fluorescent lamps (CFL or otherwise) not
only do well with very high illumination levels well into the thousands of
lux, but also there is some evidence that color closer to that of sunlight
does well, and that high spectral content of some or some other range of
blue or green-blue or blue-green wavelengths does well. Some also like to
say that sunlight-like/daylight-like color does well.
Now for something about triphosphor fluorescents of "nominal color
temperature" 4100K and higher: They have significant use of a
blue-emitting phosphor that has fairly good utilization of the UVB and UVA
wavelengths of mercury. In general, widely-used fluorescent lamp
phosphors other than that blue component in medium/high color-temp
triphosphors/CFLs utilize the big UVC wavelength of low pressure mercury
well, but largely pass UVB and especially highly pass UVA.
This means that using such sunlight-like/daylight-like colors of
CCT 4100K or higher gives you much less of UVB and UVA than the
already-low presence in CFL light of warmer incandescent-approximating
(whether successfully or not) color.
- Don Klipstein (don@misty.com) |
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