UV or not UV: that's the question, folks. The sun emits ultraviolet radiation, but
most grow lights do not, so today we're going to take a look at UV: how it
affects plants, and how, and when, to use UV emitting grow lights safely. First, a
quick recap, bear with me, it'll be really brief, I promise. PAR, or
photosynthetically active radiation, is the energy that plants use for growth
and bloom. It refers to photons, people. Discrete packets of energy traveling at
certain wavelengths, between 400 to 700 nanometers. It's also the range of
visible light energy, the colors that we humans are able to perceive, from red
through to violet. Now, I mention PAR because it sets the stage for UV. As the
name suggests, UV means beyond violet. It's radiant energy below 400 nanometers
and above 100 nanometers. Now, let me say a few important things about UV right
off the bat. UV is a broad category; it's more helpful to think of UV as UVA, UVB,
and, you guessed it, UVC. UVA is the most benign part of UV, it has the longest
wavelength-- 320 to 400 nanometers-- and carries the lowest energy. Most of the UV
that we receive from the sun falls within this range, accounting for around
6% of the total solar radiation that reaches our planet. UVB has a
shorter wavelength than UVA, and the narrowest definition of all UV subtypes.
Spanning just 280 to 320 nanometers, give or take, it forms just 1%
of the total solar radiation reaching the earth. Most of is absorbed by the
atmosphere, and this is kind of fortunate because UVB packs enough punch, people, to
inflict cell damage on living organisms and permanently change their DNA. Oh, yeah!
Last, but certainly not least, there's UVC, ladies and gentlemen. The bad boy of the
package: super high-energy, UV at 100 to 280 nanometers, effectively blocked out
by our planet's ozone layer. In terms of the electromagnetic spectrum, we're
getting close to x-rays now. Think of it like a death ray. So, as you can see, there's UV
and then there's UV. Don't be fooled by unscrupulous LED manufacturers who crow
on about how their fixtures emit UV, when there's barely anything qualifying at
around 380 nanometers. True UV-emitting LED diodes remain prohibitively
expensive, and have a really short life. However, whatever grow light technology
you're into, it's important to know what sort of UV you're dealing with and take
proper precautions. As I already said, UVC is a no-go,
but what about UVB and UVA? UVB is also dangerous: it
causes cell damage, sunburn, and skin cancer. In fact, the most destructive
wavelengths reaching the earth are between 305 and 310 nanometers. Almost in
the center of the UVB range. Many plants can actually sense the presence of
harmful UV radiation, and some, especially those native to higher altitudes in the
tropics and subtropics, have evolved their own biological coping mechanisms,
allowing them to colonize areas inhospitable to other species. So what do
they do, Everest? They produce their own sunscreen-- no, I'm not even kidding.
Simple phenolics and flavonoids, essential oils to you and me, are
produced on the surfaces of leaves and stems in response to UVB, which forms a
protective layer around the plant. As growers, this is interesting because
essential oils improve flavors, aromas, and even the vitamin and medicinal
content of some crops. Take this rosemary, for example, these cuttings have been
growing under a Gavita LEP plasma on a light-rail since they rooted. I'm using
the 41.02 grow spectrum lamp which, as you can see, has a small amount of UVB
and larger amounts of UVA, similar to the sun. After 2 months under this bad
boy, the leaves are sticky to the touch, the aromas are extremely pungent, too.
Whereas this rosemary grown under a spectrum lacking in UV is not nearly so
sticky or pungent. Now, I'm just using the LEP for veg, but many growers use plasma
lights to supplement their HPS during flowering. This is notable because high
ratios of PAR to UVB, as well as UVA to UVB, have been shown to lessen the damage
effective UVB. Conversely, too much UVB without enough UVA and PAR can
exaggerated cell damage. Once again, amigos, it all comes down to spectral
quality. LEC, or light emitting ceramic, fixtures running Philips CDM lamps have
increased levels of UVA and UVB compared with standard metal halides, old-school
HPS, or double ended HPS. Double ended metal halide lamps pack a great UV punch,
especially high Kelvin lamps, such as this Ultra Sun 10,000 Kelvin lamp. The
catch, however, is that it must be operated in an enclosed reflector for
safety reasons and the glass panel will filter out the potentially useful UVB.
Finally, there's T5 fluorescent technology available, too. Eye Hortilux
offering their PowerVeg Full-Spectrum, plus UV lamps and 2 and 4 foot models
and the Ultra Sun offer a 4-foot lamp. Either can be used in regular high-
output T5 fluorescent fixtures. Don't forget, if you're working with UV lamps,
always wear sunglasses-- your future so bright you gotta wear shades-- and avoid
prolonged exposure. I'm sure this video is going to generate more questions than
it answers, but that's all good. Deposit them in the comments below. Take
care of yourself, and your plants, kitties, and stay sunscreen-slathered up. This is
Everest, leaving your visible spectrum, good-bye!