On Aug 10, 8:24*pm, (Don Klipstein) wrote:
In ,

wrote:
On Aug 10, 5:23*pm, (Don Klipstein) wrote:
* Except that the main germicidal wavelngths of UV (UVC of wavelength
around 240-280 nm) are highly blocked by the ozone layer

What about UV lights? Do they have the desirable germicidal effect?

* That depends on what the UV lights are. *There are a few varieties of
UV!

* Longer wave 65% or so of UVA, 340 to 400 nm or so: *This is the
"blacklight range", as in the main wavelength range for dim violetish
color lamps to cause organic fluorescent substances to glow.

* This wavelength range has its "traditional base" being the 365-366 nm
cluster of wavelengths of high pressure mercury vapor lamps. *Blacklight
"fluorescent lamps" (those are actually true fluorescent lamps) of BL and
BLB types have a phosphor that absorbs the 254 and 185 nm main wavelengths
from glowing low pressure mercury vapor to produce fluorescence in
longer-wave UV around 360 nm.

* There are many UV LEDs with peak wavelength around 395 nm, and fewer
with shorter wavelengths but still mostly at least 350 nm. *When an LED
has nominal peak wavelength 350-375 nm, it tends to dimly visibly glow
with a violetsh-white color - due to weak out-of-main-band spectral
content combined with the visible-violet-fringe of the main UVA emission
band.
* When a UV or "near-UV" or "nearly-UV" LED has peak wavelength in the
380 to 410 nm range, especially of 395 or 400 or 405 nm common
wavelengths, such an LED is typically quite violetish in color and often
not especially dim. *400 nm is the "official border" between UVA and
"visible light", LEDs with peak wavelength slightly below 400 nm have
their main emission bands having some significant spectral content at
wavelengths above 400 nm, and "near-UV" of wavelengths only slightly
shorter than 400 nm is dimly visible.

* The main human health hazards from longer-UVA wavelengths a

* *To the lens of the eye (mainly impacting farm hands and long-haul truck
* drivers working heavily within roughly 35 degrees latitude from the
* equator).

* *To the retina of the eye, mainly from focused intense images of strong
sources of such UV such as staring into a UV LED.

* Next shorter wavelength significat subdivision of UV: *Tanning UVA.
That is roughly 315-340 nm.
* Keep in mind that "tanning UVA" is not completely harmless to human
skin, and can also be harsh on the retina, lens and cornea of the human
eye.

* Next after that is UVB - 280 to 315 nm. *That is a harsher range of UV.
UVB content in sunlight reaching Earth's surface is mostly 300-315 nm.

* Ill effects to the human eye from shorter wavelengths of UV tend to be
more concentrated to more-foreward parts of the human eye. *UVB has some
prospect to do bad things to the lens of the human eye, but is worst to
the cornea.
* UVB is notably harsh on human skin and blamed for many skin cancers,
especially ones of the more-malignant class of "malignant melanomas".

* Next down in UV categorization by wavelength is non-vacuum portion of
UVC. *That is 200-280 nm. *"Germicidal UV" is mainly the longwave 50-60%
or so of this range, and the shortest UVB wavelengths are indeed are
slightly to somewhat germicidal. *The 254 / 253.7 nm wavelength from low
pressure mercury vapor (combined appropriately with a "noble gas" or a
mixture of "noble gases") is the main wavelength for such purpose from
lamps made for such purpose.

* The main human health hazards from UV wavelengths that short are to the
conjunctiva and outer regions of the cornea of the eye, and to the
epidermis of the skin. *Carcinogenesis to human skin from UVC appears to
be a significant problem from significant exposure, and appears to be
likely confined to the epidermis - where the more malignant skin cancers
of "malignant melanoma" type tend to originate.
* Just to point out an alarmist thing to watch for - there is such a
thing as non-melanin-producing malignant melanoma. *That is an uncommon
but deadly known "subvariant" skin cancer whose critical early warning
sign is otherwise-unexplained growth of a reddish area on the skin,
mole-like small or almost that small in size when it is in an earlier
stage when having a dermatologist removing it has a good chance of saving
your life from removing such a deadly cancer at such a sufficiently early
stage.

* UV wavelengths in the UVC range also include the 10 to 200 nm range as
well as the 200-280 nm range. *The sub-200-nm wavelength range is "vacuum
ultraviolet" "AKA VUV", absorbed by air and oproducing ozone in the a
process. *Few transparant solid materials pass significantly even a part
of this wavelength range.
* The main wavelength of low pressure mercury vapor in this range is 184.9
AKA 185 nm.

*- Don Klipstein )

Skin cancer is over blown. No one ever died from it. Lots of people
who've spent most of their lives outdoors live to be over 100. Get out
more. Furthermore I ain't gonna be sunbathing by my water tank. So
skin exposure isn't even an issue, nor eye problems. I'll black it out
from view if it get annoying.
.. off to get me some UV.