A translucent woven ripstop film
sold by Shelter Systems
transmits a percentage of the UVB radiation. 140 µW/cm2 48" beneath the
roof cover may not seem like much compared to the 300 µW/cm2 of unfiltered
sunlight, but compared to the zero UVB photons emitted by HID bulbs or
transmitted by corrugated fiberglass and other regular greenhouse coverings, a UVB level of 140 microwatts/cm2 is
quite a lot. Installs nicely in an aluminum window screen frame. Rating: excellent hide.
Unfiltered sunlight@11:00am = 300 µW/cm2
48" beneath ripstop film@11:00am = 140 µW/cm2
The following UVB readings were taken beneath new 3 mil. polyethylene
translucent plastic sheeting purchased at the local hardware store.
Polyethylene plastic sheeting will break down under direct sunlight and may not
last much longer than six weeks before it starts to split. Rating: fair
hide.
Even though the actual µW/cm2 of UVB photons required to make fully realized
THC is not known for sure, four 160-watt Active UVHeat
mercury vapor lamps produced enough UVB photons to
give the desired effect to the resin spheres on pollinated marijuana grown
indoors---in 16 sq ft, under a corrugated fiberglass roof that transmitted zero
UVB photons---when compared to other resin spheres that received no UVB
photons. The potency of the harvested resin spheres illuminated by the
specialized incandescent light bulbs were on average about the same as the harvested resin
spheres from plants grown outdoors that were in direct sunlight only from 11am
to 4pm in September and October during the six weeks it took the majority of
seeds to ripen after the collective ovum were fertilized in
mid-September. The reason for the potency seeming to be nearly the same
could be explained by the fact that most of the outdoor UVB photons available
to the resin spheres were reflected and had an average intensity of only 50
µW/cm2 or so based on measurements taken at different times of day on the sides
of the plants that were not in direct sunlight.
The main obstacle to conveniently substituting artificial light UVB photons for
the UVB photons in sunlight is
that UVB intensity falls off according to the Inverse Square Law,
which is why the specialized light bulbs had to be between 12" and 8" from the
target
floral bract clusters
for the UVB to have enough intensity to provide the desired
effect. The UVB intensity of the GE Daylight ULTRA 6500K fluorescent
tubes is also affected by the Inverse Square Law: At 2" the UVB µW/cm2 reading
is 27; but at 12" it is only
8.
All UVB readings were made with the
Solartech Model 6.2 meter
Click here for a list of other sources of UVB and UVB transparent coverings.
The views expressed here by
the writer are his alone except where
indicated.
copyright 2003 George Grass rev 2004 2006
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.