This is a very fascinating thread. What do you guys think about this? Would anyone suggest how much uva uvb should be added in a 4x8x80 tent?
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UVB: There is some evidence that UVB radiation is effective at inactivating other SARS viruses (not SARS-CoV-2). However, it is less effective than UVC at doing so and is more hazardous to humans than UVC radiation because UVB radiation can penetrate deeper into the skin and eye. UVB is known to cause DNA damage and is a risk factor in developing skin cancer and cataracts.
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That’s good to know, I’m adding uvb come mid or late flower next run, I’ll make sure to stay out the tent when it’s on. It’s like what an hour or so a day?
Hey corey in a 4X8X80 tent I would put two four foot UV-B bulbs running down the length of the grow, for best coverage. Or get one and see what having it on half of your grow does to that side of your crop, for comparison.
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I don’t think that’s true. UVC is higher energy radiation it wouldn’t make sense that UVC is less damaging considering the wavelength is smaller. X ray is right beside UVC on the spectrum.
How Ultraviolet Radiation Affects Plants with Dr. Bruce Bugbee - YouTube good info for those who haven’t already seen
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The atmosphere does little to shield these rays—most UVA radiation reaches Earth’s surface. UVA rays cause skin aging, and eye damage and can lower your body’s ability to fight off illness. UVA rays also contribute to the risk of skin cancer.Ultraviolet B rays (UVB)
The Earth’s atmosphere shields us from most UVB rays—the amount of UVB rays that reach the Earth’s surface depends on latitude, altitude, time of year and other factors. UVB rays cause sunburns, skin cancer, skin aging, and snow blindness (a sunburn to your cornea that causes a temporary loss of vision) and can lower your body’s ability to fight illness.Ultraviolet C rays (UVC)
UVC rays do not reach the Earth’s surface because they are completely absorbed by the atmosphere. Harmful effects from UVC rays are minimal.
Eyes
The epithelial cells of the cornea absorb radiation in the actinic portion of
the UV spectrum (200 – 315 nm). This exposure produces symptoms
known as photokeratitis, which are not felt until several hours after the
exposure. Photokeratitis is very painful and produces the sensation of
having sand in your eye. It also causes an aversion to bright light, as well
as the production of tears. The effects typically last up to 48 hours but will
disappear as the cells of the cornea are replaced.
Long-term effects can also occur. Most of the UV radiation that enters
the eye is absorbed in the cornea, but UVA absorption by the lens can
alter proteins in the lens and result in cataract formation.
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All UV is damaging. As individuals, we don’t have a whole lot of experience with UV-C since most don’t usually experience exposure to it often. Likewise to the FDA claim regarding penetration, UVA penetrates deeper into the skin and the eye as well. Let’s review some of this to get a better feel as to what is being discussed.
Here is a different take from the WHO:
Short-wavelength UVC is the most damaging type of UV radiation. However, it is completely filtered by the atmosphere and does not reach the earth’s surface.
Medium-wavelength UVB is very biologically active but cannot penetrate beyond the superficial skin layers. It is responsible for delayed tanning and burning; in addition to these short-term effects it enhances skin ageing and significantly promotes the development of skin cancer. Most solar UVB is filtered by the atmosphere.
The relatively long-wavelength UVA accounts for approximately 95 per cent of the UV radiation reaching the Earth’s surface. It can penetrate into the deeper layers of the skin and is responsible for the immediate tanning effect. Furthermore, it also contributes to skin ageing and wrinkling. For a long time it was thought that UVA could not cause any lasting damage. Recent studies strongly suggest that it may also enhance the development of skin cancers.
For the three bands of UV radiation, the maximum personal exposure limits is considered as follows:
UV-A 1000uW/cm2 for 8 hrs
UV-B 500 uW/cm2 1 min
UV-C 100 uW/cm2 1 min
If you bask in any of these you will get ‘sunburn’ or other ill effects, the exposure duration decrease as the energy levels increase. Unfortunately, the majority of studies on the effect of UV on the skin is mainly limited to UV-B, UV-A as UV-C irradiation is predominantly absorbed by the atmosphere. But, we can develop a sense as to what this means.
From the sunlight graph earlier, the UV-B irradiance on that particular day was approximately 29 uW/cm2. While not an accurate assessment, going strictly by an integrated exposure, you’d exceed the exposure limit in ~17 minutes by being outside. This more or less corresponds to the suggestions regarding sun exposure as follows with increasing skin pigmentation:
| Skin type | Maximum amount of time |
|---|---|
| I | 10 minutes |
| II | 20 minutes |
| III | 30 minutes |
| IV | 50 minutes |
| V | more than 60 minutes |
| VI | more than 60 minutes |
For the Fluence UV Spec fixture, noted earlier, approximately 20% of the irradiation is UV-A while a small portion is UV-B. The fixture produces approximately 35 W/m2 which corresponds to 700 uW/cm2 UV-A and 0.7 uW/cm2
Further, we can explore the action spectra:
The erythema action spectrum is widely used in assessing the negative effects of UV radiation sources (most frequently the sun) on human skin. Strictly, the action spectrum is for erythema (sunburn), but it is also used as a proxy in quantifying UV for other UV effects, e.g. skin cancer, vitamin D synthesis and even effects on plants and sometimes for weathering.[1]
And,
chang2008.pdf (372.8 KB)
What you’ll notice is that exposure to UV-C has a erythemal dose (skin) that is significantly greater than that of UV-B when near the radiation source. Beyond 25 cm or so, the two show an equivalent dose with UV-C likely continuing to decrease. The time scales are of consideration with the maximal exposure to UV-C near the source being approximately half of that of UV-B. The difference is namely due to absorbance versus distance. Conversions, 5 cm is approximately 2 inches while 30 cm is approximately 12 inches.
Now, the eye is a different beast entirely. UV-C will primarily effect the surface of the cornea, UV-B will namely effect the mass of the cornea, UV-A will mostly pass through and affect the retina. Both UV-C and UV-B can cause issues with the cornea … ever had that sandy / dry /gritty feeling … sometime even blurred vision. I’d suggest that the surface area relative to the volumetric area of the cornea are going to differ and likewise the absorbed power per unit of area will differ. The effect of exposure is likewise going to differ in regards to time. Likely UV-A could also effect the cornea with long enough exposure. I have not looked at the literature as of yet, so this is currently a presumption.
In all cases, as noted earlier, take appropriate precautions when around UV. Don’t use you UV fixture as a disco light, don’t stare into to it, limit exposure. Higher energies can cause higher physical harm.
Ancillary graph of interest (only UV-A and B).
[2]
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i’m doing my own led panels… planning to make a business around this later… so this thread is high interesting to me !
i’ve found this page Busting common myths about cannabis and UV and some information there makes sense to me:
You only need UV light for the last 2/3/4 weeks of flowering
Not exactly. You can use UVB (UVA is much less helpful in this situation) only in the last few weeks and yes, it will be better than if you didn’t, but you are missing out on the true potential of UVA/B. In the wild, plants don’t get UV just in the last 2 to 4 weeks. In fact, they get much LESS UV during the last month of flowering than they do during veg simply because of the angle of the sun. Plants will absolutely produce more trichomes, more THC if you use a proper UVB bulb during the entire flowering season. In fact, most larger, successful growers will run them an hour a day during the last half of veg to harden them, and to kill off any risk of powdery mildew.
looking this thread, maybe this behavior its more connected about the lifetime of the ligths than the worth of the use, right ?
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Some context is missing in the epa article since it is alluding to the sun yet the title is tanning equipment.
The eye for me is the main concern. UV radiation of any wavelength can be damaging. Too little is understood about uvc to say, but users should understand there is risk involved.
Granted probably no more than say a mechanic with his hands in gasoline/oil all the time. (people wear gloves these days, but it’s rather recent)
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Well on an interesting note they use UVC to destroy bacterial, viral or fungal DNA in hospitals.
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i’ve read something telling the same for indoor grows… The UV helps to keep insects and fungus out.
You have to dig a bit but generally the LEDs in the UV range have had short lifetimes relative to PAR range LEDs. They are also pricey. Typically there is a metric, that I can’t quite recall, where a 20% decrease in output, or thereabouts, is considered the device lifetime.
There are a variety of effects. UV damages the materials (e.g. the clear encapsulation) or perhaps displacement damage due to the higher energies involved.
Example (365nm):
[1]
Another (365nm):
This technology is improving over time and the above examples mostly reflect encapsulation material damage (which decreases output and increases temperature). Dig around via Mouser / Digikey for some of the individual LEDs and then track down reliability information via the OEM (e.g. Vishay, Lumix, etc) to get an idea of the current performance and lifetimes. I’d be interested in learning where things are at today.
For building a fixture, until the relative lifetimes are improved, I’d say have the UV as a separate fixture.
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I’m using their buddies as side lighting in my current grow stuck to the tent under the canopy, they’re a pretty neat product!
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Hello corgitron I have yet to post a grow log on OG. I plan to post some mutants I have just sprouted soon though.
Hey Dirt_Wizard, thanks you for saying so. I’m crazy in love with GLA boards so far. Now I want to build a dedicated clone area, and those buddies seem like a perfect fit to any area.
I have known the guy that worked building and crafting the led’s to what they offer. He has been on the weed boards for many years, a fountain of knowledge.
Best to ya!!
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I have a 100w (actual) strip with Cree 3w violet a and royal blue. Any thoughts on what would happen if I supplemented with it in my tent during flower? I’ve seen conflicting info…
Also, has anyone tried the Cree violet bulbs?
Many thanks!
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