Radiation Exposure in Sailplanes

I've posted this before and hope I'm not boring everyone.

Using an excellent and expensive Crawford UV meter and testing a whole
line-up of gliders one day there was a distinct pattern of older
gliders passing UV and newer gliders not. *Eric, one of these days
I'll be out at EPH the same time as you are and we can do some
research on the line-up out there, but we won't get wavelength charts


Now we're talking evidence instead of anecdote! Can the meter quantify
the difference in transmission?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Well, the meter reads out total UV/sq.meter and UV as a % of total
light energy measured in microwatts per lumen ( –µW/ l) so if the
source of UV remains constant you could get a sense of the comparable
values, yes. Usually the source is daylight and it's changing from
moment to moment so an exact measurement would be tricky. In reality
what happens is that you stand next to a glider with the meter reading
huge amounts of UV and when you put the meter under the canopy of a
newer glider there is a radical drop in the reading. Because this is
indicating UV as a % of available light the tinting is not a factor at
all unless the tinting is reducing visible light but not blocking UV,
which I have seen in some residential glazing products. Anyway, DG
gliders for example have UV reduction to the point that I don't think
it's a factor at all. I still get sunburned but it's while I'm
rigging and not while I'm flying and I think that is going to be true
for many (most) other gliders and their owners. In museums there is
this blue fabric that they scatter around that fades at a given rate
in the presence of UV and works as a warning, it would be nice if
there was something like that for this application.

Brian


Brian

On Feb 13, 8:29*pm, brianDG303 wrote:
I've posted this before and hope I'm not boring everyone.

Using an excellent and expensive Crawford UV meter and testing a whole
line-up of gliders one day there was a distinct pattern of older
gliders passing UV and newer gliders not. *Eric, one of these days
I'll be out at EPH the same time as you are and we can do some
research on the line-up out there, but we won't get wavelength charts

Now we're talking evidence instead of anecdote! Can the meter quantify
the difference in transmission?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Well, the meter reads out total UV/sq.meter and UV as a % of total
light energy measured in microwatts per lumen ( –µW/ l) so if the
source of UV remains constant you could get a sense of the comparable
values, yes. *Usually the source is daylight and it's changing from
moment to moment so an exact measurement would be tricky. *In reality
what happens is that you stand next to a glider with the meter reading
huge amounts of UV and when you put the meter under the canopy of a
newer glider there is a radical drop in the reading. *Because this is
indicating UV as a % of available light the tinting is not a factor at
all unless the tinting is reducing visible light but not blocking UV,
which I have seen in some residential glazing products. *Anyway, DG
gliders for example have UV reduction to the point that I don't think
it's a factor at all. *I still get sunburned but it's while I'm
rigging and not while I'm flying and I think that is going to be true
for many (most) other gliders and their owners. *In museums there is
this blue fabric that they scatter around that fades at a given rate
in the presence of UV and works as a warning, it would be nice if
there was something like that for this application.

Brian

Brian

The entire document below is available at http://www.plexiglas.com/literature/pdf/81.pdf

Plexiglas sheet absorbs the shorter wavelengths of
ultraviolet (UV) energy, but transmits most of the
longer wavelengths (those near the visible region),
Figure 5.The UV transmittance, unlike the visible
and infrared transmittance, of colorless Plexiglas sheet
varies from one formulation to another.Therefore,
Plexiglas MC sheet does transmit slightly more of the
longer UV wavelengths than does Plexiglas G sheet.
Even after prolonged outdoor or artificial light
exposure, the spectrophotometric characteristics of
Plexiglas sheet in the UV and visible ranges do not
change significantly. Most of the drop in UV transmittance
of Plexiglas sheet takes place in the first two
years after exposure to sunlight. No measurable change
occurred in the spectrophotometric curves of these
exposed samples between 5 and 10 years outdoors.
Colorless Plexiglas sheet exhibits the same excellent
resistance to discoloration when exposed for 20 years
or more to constantly lit fluorescent lamps, even when
the Plexiglas sheet is only two inches from the lamp.
This unsurpassed UV stability gives Plexiglas sheet
superb weatherability and makes it the logical choice
among plastic materials for outdoor and artificial
lighting applications. Other transparent plastic materials
tend to yellow or develop appreciable haze levels
when exposed to UV energy.
The spectrophotometric curves in Figure 5 show the
light transmission of colorless Plexiglas sheet formulations
in the UV bands of the electromagnetic spectrum.
Note that regular Plexiglas G and MC sheets block
some portions of the UV spectrum, but special grades
are needed when virtually all (UF-3/UF-5) or most
(UF-4) of the UV wavelengths must be excluded.
PLEXIGLAS ULTRAVIOLET–
FILTERING FORMULATIONS
Some special formulations of Plexiglas acrylic plastic
have spectrophotometric characteristics that enable
them to filter out almost all of the UV energy.These
formulations are available in both sheet and molding
resins. Plexiglas UV-filtering materials offer protection
from structural damage caused by exposure to UV
wavelengths shorter than 400 nanometers. However,
since these materials do not appreciably filter visible
light in the critical lower violet range from 400 to
500 nanometers, they will not completely prevent
colors from fading or darkening.
Limiting exposure to light is only one of the steps that
can be taken to slow the deterioration of materials.
Factors such as temperature, humidity and atmospheric
contamination will also affect this process.
Three Plexiglas sheet formulations that can filter
UV light are available. Plexiglas UF-4 sheet absorbs
most ultraviolet radiation. Plexiglas UF-3 sheet
absorbs virtually all ultraviolet radiation and some
of the visible light in the violet wavelength region.
Plexiglas UF-5 sheet, a new, special formulation in
the MC grade for framing applications, filters the
maximum of harmful UV radiation. Figure 5 compares
the spectrophotometric curves of these three grades
with those of standard colorless Plexiglas G and
Plexiglas MC sheets. Note that the spectrophotometric
characteristics of the three Plexiglas UF sheet
formulations are the same, regardless of the thickness
of the sheet. Comparatively, the spectrophotometric
characteristics of Plexiglas G and Plexiglas MC sheets
change with thickness.
Plexiglas UF-3 and MC UF-5 sheets are the most
effective of the ultraviolet-filtering formulations of
Plexiglas acrylic. Not only do these materials absorb all
ultraviolet radiation (390 nanometers and below), but
they also absorb part of the relatively harmful visible
light in the critical violet (400-450 nanometers)
region. Plexiglas UF-3 sheet does absorb some visible
light, therefore it has a very faint yellow edge tint.
This tint is not objectionable in most applications.
Plexiglas UF-4 sheet may be used for those applications
in which the slight yellow tint of the other
materials is objectionable, such as unframed display
cases. Plexiglas UF-4 does transmit slightly more UV
energy than its counterpart, and, as a result, it is
somewhat less effective in retarding fading or darkening
of colors caused by visible light in the 400 to 500
nanometer range.

At 06:06 20 February 2011, 2G wrote:
On Feb 13, 8:29=A0pm, brianDG303 wrote:
I've posted this before and hope I'm not boring everyone.

Using an excellent and expensive Crawford UV meter and testing a
whol=
e
line-up of gliders one day there was a distinct pattern of older
gliders passing UV and newer gliders not. =A0Eric, one of these
days
I'll be out at EPH the same time as you are and we can do some
research on the line-up out there, but we won't get wavelength
charts

Now we're talking evidence instead of anecdote! Can the meter
quantify
the difference in transmission?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us"
to
email me)



“Plexiglas sheet absorbs the shorter wavelengths of
ultraviolet (UV) energy, but transmits most of the
longer wavelengths (those near the visible region),
Figure 5.The UV transmittance, unlike the visible
and infrared transmittance, of colorless Plexiglas sheet
varies from one formulation to another.Therefore,
Plexiglas MC sheet does transmit slightly more of the
longer UV wavelengths than does Plexiglas G sheet.
Even after prolonged outdoor or artificial light
exposure, the spectrophotometric characteristics of
Plexiglas sheet in the UV and visible ranges do not
change significantly. Most of the drop in UV transmittance
of Plexiglas sheet takes place in the first two
years after exposure to sunlight. No measurable change”

“Three Plexiglas sheet formulations that can filter
UV light are available. Plexiglas UF-4 sheet absorbs
most ultraviolet radiation. Plexiglas UF-3 sheet
absorbs virtually all ultraviolet radiation and some
of the visible light in the violet wavelength region.
Plexiglas UF-5 sheet, a new, special formulation in
the MC grade for framing applications, filters the
maximum of harmful UV radiation.”


From reading this material we are led to believe that most acrylic
Plexiglas does not transmit most UV light and does not degrade much itself
when exposed to sunlight.

Why then the high rate of UV transmission in older canopies? Was there a
different formula for the acrylic that was used to make canopies in the
70s and 80s? If so, when did the formula change?

Have these older canopies degraded over time due to exposure or were they
always unable to filter UV?

R5