[Lost in a SOG]

Yeah pest control is a major consideration with uv supp. also for killing fungal spores on flowers..

This pretty legit article would suggest only the 280-300nm range is worth adding. It delivers 10x the amount of activation needed for secondary metabolite formation(epigenetic changes) than 300-310..

Just hitting this wavelength alone will deliver seemingly all the benefits in the most efficient way and without any of the rest of the UV spectrum, most of which will only damage the plants.

Many UV bulbs ive seen only start after 300nm and up so will be badly tuned to hit this 280-300nm sweet spot.

I reckon this will make a huge difference and explain why guys like SamS didnt find any benefits, in fact only damage.. below 280 though and you're into C..

UV LEDS IN HORTICULTURAL LIGHTING

Among the most compelling of presentations at the conference was a talk focused on the use of UV spectrum in horticulture. Peter Barber (Fig. 2), director of product marketing and business development at SETi, presented "The myriad ways that UV LEDs will impact society through horticultural lighting."*SETi is a UV technology specialist that was acquired by Seoul Viosys in early 2016. Seoul Viosys is focused on UV LEDs and is a sister business to visible-light LED manufacturer Seoul Semiconductor.

Barber briefly discussed lighting in the PAR region before jumping into the UV topic with the proclamation that UV energy has applicability over the complete cycle of vegetable growth and consumption, or what he termed "seed to belly" with the farmer of course in the middle of the cycle. Seedlings can benefit from UV energy in two ways, according to Barber - UV treatments can strengthen root systems and can prevent or suppress mold.

FIG. 3.*LESA's Tessa Pocock projected a future in which sensors would enable a closed-loop system for horticultural lighting where plants would tell the system what they need.

For the farmer, mold suppression remains a UV benefit, but there are many additional benefits. As we have covered previously,*UV energy can influence the appearance, smell, and taste of plants. Indeed, UV energy can increase nutritional value or perhaps potency in the case of a cultivar such as cannabis, according to Barber.

There are secondary uses for UV lighting in a farm as well. For example, it can be used to disinfect hydroponic lines that feed water and nutrients to plant roots. We covered such a usage*in a shipping-container-based vertical farm. UV exposure can also increase the shelf life of products after harvest, benefitting the farmer and the consumer. Barber said UV light can even be used to treat mold spots on produce.

SECONDARY METABOLITES

Still, it's the impact on the look, flavor, and potency of a plant that may be the most interesting result of UV light in horticulture, and Barber explained some of the details of plant physiology relative to UV exposure. In response to UV-B spectral energy (UV-B is the middle UV band spanning 280-315 nm), a plant reacts through a stress mechanism to protect itself. The Mitogen-Activated Protein Kinase signaling - MKP1/MPK3/MPK6 - initiates the response.

A molecular signaling pathway called UVR8 then is responsible for increased secondary plant metabolites such as flavonoids in vegetables or THC in cannabis. But the plants are very selective in terms of the spectra to which they react. Barber used the analogy of an arcade skee ball game where the inner targets deliver more points to the player than the outer targets.

Barber said UV emission in the range of 280-300 nm only requires a fluence rate of 0.1 μmol/m2/sec to achieve the desired boost for secondary metabolite production. A plant would need ten times more energy from emission in the 301-310-nm band. Barber said, "That's why LEDs are so preferred. You can provide that targeted region." That statement could apply to LEDs in the PAR and other bands as well as to the UV energy that Barber was discussing.

The mechanism by which the plant reaction occurs is due to a plant's epigenetic memory, according to Barber. As an example, he said cannabis grown at high altitude in Colorado has higher concentrations of THC and terpenes than do plants grown at sea level. The plants grown at higher altitude get more UV. Barber likened the plant reaction to a natural sunscreen. And he pointed out that sporadic exposure can trigger the reaction. Conversely, too much exposure can lead to cell death. Barer said the closer you get to 280 nm, the greater the risk for permanent damage, noting that "UV-C is unbiased when it comes to DNA" and that it would destroy cells.

https://www.ledsmagazine.com/article...entations.html

[Ibechillin]

Originally Posted by Lost in a SOG

This pretty legit article would suggest only the 280-300nm range is worth adding. It delivers 10x the amount of activation needed for secondary metabolite formation(epigenetic changes) than 300-310..

Out of rep for today haha, great find Lost in a SOG!

[Lost in a SOG]

Thanks

This is super interesting.. and relevent regarding usage and safety of deep uv in horticulture.

https://onlinelibrary.wiley.com/doi/...1111/lam.12301

Suppression of*Tomato mosaic virus*disease in tomato plants by deep ultraviolet irradiation using light‐emitting diodes

Abstract

Resistance‐breaking strains of*Tomato mosaic virus*(ToMV) are emerging in many countries, including Japan. We examined whether deep ultraviolet (UV) irradiation on tomato plants using light‐emitting diodes (LEDs) could suppress the expression of ToMV symptoms. We also investigated the optimum wavelength and radiant exposure for suppressing the disease effectively in tomato plants. Among the three wavelengths tested, UV irradiation at 280–290*nm had a relatively high suppressive effect on ToMV and resulted in a low incidence of UV damage. Pre‐inoculation exposure to UV was effective in suppressing viral disease, indicating that acquired resistance was induced by UV irradiation. UV‐B fluence of 0·7–1·4*kJ*m−2*day−1*at wavelengths of 280–290*nm suppressed ToMV effectively without significant UV damage.

Suppressive effects of each UV wavelength

We used LEDs of different wavelengths to evaluate the suppression of ToMV disease by UV irradiation. In non‐UV‐irradiated plants, severe yellowing and necrotic spots occurred on the upper leaves (third and fourth true leaves) of the tomato plants, which showed dwarfing 7*days after virus inoculation (Fig.*1c). In contrast, disease severity was significantly lower in plants irradiated with UV at wavelengths of 290*nm or less than in the non‐UV‐irradiated controls (P*<*0·01) (Figs*1a,b and*2a). Disease severity in plants irradiated with UV at 295–305*nm was similar to that in non‐UV‐irradiated controls (Fig.*2a). The amount of target ToMV RNA per total RNA (μg) was significantly lower in plants irradiated with UV at wavelengths of 290*nm or less than in non‐UV‐irradiated controls (P*<*0·001) (Fig.*2b). In contrast, the amount of viral RNA in plants irradiated with UV at 295–305*nm was not significantly different from that in the non‐UV‐irradiated controls (Fig.*2b). Severe UV damage, with leaf curl and size reduction, was observed on plants irradiated with UV at 260–270*nm; the UV damage caused by UV irradiation at 280–290*nm was milder than that caused by irradiation at 260–270*nm (Fig.*1a,b).

Pre‐ and post‐inoculation UV irradiation

We evaluated the effects of UV irradiation timing on the incidence of ToMV disease in tomato plants. Disease severity was significantly lower in plants irradiated with UV (280–290*nm) than in non‐UV‐irradiated con‐trols, regardless of the timing of irradiation (P*<*0·01) (Fig.*3a). The amounts of viral RNA in plants irradiated with UV (280–290*nm) before (P*<*0·001) and after (P*<*0·01) virus inoculation were significantly lower than in non‐UV‐irradiated controls (Fig.*3b).

We found here that the suppressive effect of ToMV was high even when tomato plants were irradiated with UV‐B only before inoculation. These results suggested that acquired resistance to ToMV in tomato plants was induced in advance by UV irradiation. The mechanism of virus suppression in tomato plants by UV irradiation may mainly be a reduction in ToMV multiplication, because suppression of ToMV was also observed upon UV irradiation after virus inoculation. The suppressive effect observed when the plants were UV irradiated after inoculation was slightly inferior to the effect when irradiation occurred pre‐inoculation. Therefore, exposure to UV‐B before virus infection is an important strategy for controlling viral diseases.

The UV damage in tomato plants irradiated with UV at wavelengths of 280–290*nm with various radiant exposures for 7*days is shown in Table*1. There were no significant differences in weight of the above‐ground parts of plants among the radiant exposures (P*=*0·3359). Although distinct or severe leaf curl was observed in tomato plants irradiated with UV at 1440*J*m−2*day−1, little or no leaf curl was observed at <720*J*m−2*day−1. Neither chlorophyll concentration nor chlorophyll fluorescence differed significantly among treatments.

When tomato plants were irradiated with UV at wavelengths of 280–290*nm, a radiant exposure of 720*J*m−2*day−1*or more at the leaf surface significantly reduced ToMV disease incidence and virus accumulation compared with those in the non‐UV‐irradiated controls. In contrast, a sufficient virus‐suppressive effect was not observed at a radiant exposure of 360*J*m−2*day−1. Substantial UV damage, including decreased chlorophyll content and photosynthetic decline, was not observed at radiant exposures of 1440*J*m−2*day−1*or less, although distinct leaf curl was observed at 1440*J*m−2*day−1. These results suggest that the optimum UV radiant exposure for suppressing ToMV disease in tomato plants but avoiding UV damage is in the range of 720–1440*J*m−2*day−1.

LEDs have the advantage of being able to emit specific, narrow wavelengths with high energy efficiency. We were able to suppress a resistance‐breaking strain of ToMV by UV‐B irradiation at wavelengths of 280–290*nm and a fluence of about 0·7–1·4*kJ*m−2*day−1using LED modules, thus inducing acquired resistance in tomato plants with a relatively small degree of UV damage. To the best of our knowledge, this study is the first to suppress a plant virus in a susceptible crop using LED lighting, thereby allowing us to control ToMV using deep UV LEDs under practical conditions such as the nursery beds of plant factories, where initial viral infection can cause devastating damage to tomato production

Happy growing!

[led05]

Originally Posted by Lost in a SOG

Yeah pest control is a major consideration with uv supp. also for killing fungal spores on flowers..

This pretty legit article would suggest only the 280-300nm range is worth adding. It delivers 10x the amount of activation needed for secondary metabolite formation(epigenetic changes) than 300-310..

Just hitting this wavelength alone will deliver seemingly all the benefits in the most efficient way and without any of the rest of the UV spectrum, most of which will only damage the plants.

Many UV bulbs ive seen only start after 300nm and up so will be badly tuned to hit this 280-300nm sweet spot.

I reckon this will make a huge difference and explain why guys like SamS didnt find any benefits, in fact only damage.. below 280 though and you're into C..



https://www.ledsmagazine.com/article...entations.html

Here’s a widely available bulb that is ideal for focused UVB, I agree, Sammy’s studies were woefully inadequate. I’ve tested many Bulbs for UVB with a Solarmeter; the below linked bulbs are strongest, best & cheapest you’ll find BY Far. I’ve posted about this in past across other UVB threads fwiw

Mid range 306nm is what you want; not sure I’ve ever found a bulb with better SD; this bulb is ideal for Vitamin D synthesis in humans btw too. Works on your Psoriasis as well

https://www.ushio.com/files/specific...blacklight.pdf

That study has a lot of agenda (LED sellers) to it but IME the sweet spot is 285-310nm and is and has been readily available for years as Medical & Industrial grade fluros

Cheers

[f-e]

I have to wonder if brief uv-c flashes might trigger the plants defenses better. It that's whats happening.

I have a uv-b lamp here about to try it. 10% uv-b, 25w CFL for £15. Yes £15 while a separate lamp and ballast was more like £50. That's a huge difference. Just £10 bagged me a vert like shade to suit.

Putting plants outside I sometimes see white leaves after the first week. I think that's uv as I don't bother hardening them off. So will try and get it in early to grow resistant plants. Probably keeping it high, then lowering it.

My mind is circling around movement sensors to switch it off.

[Lost in a SOG]

f-e.. I have to wonder if brief uv-c flashes might trigger the plants defenses better. It that's whats happening.

Yep you are spot on there.. good wondering. But the highest frequency of deep UV.. the research seems to suggest any exposure to this frequency will elicit the response in plants but i can only assume from what ive read it will obviously have a bell curve relative to intensity and duration.

Movement sensors to detect you in there?

I wouldnt bother personally, if you were basking naked within a couple feet for hours then maybe..

I doubt any UV flouro or really anything we have had access to for a while has really been worth while using..

The same magic spot between 285 and 310 is not only according to research the perfect sweet spot for plants its also more ideal for human vitamin D production than the sun, again because it elicits the production of this life saving metabolite without the rest of the UV spectrum being there, needlessly cooking you.

So ive just bought a couple of these:

https://www.digikey.co.uk/product-de...010-ND/7363765

Ill run them at a slightly higher V to hit the 285nm.

This band around 280-310 has been super difficult for them to hit in the LED industry and provide great efficiency, well those days are with us..

These are also being used in portable water sterilizing bottles as we speak. Which is an awesome gadget.. think solar powered portable water sterilizing, thats progress!

I will report back and hopefully ill get to use them on the girls i have in flower now for the final weeks. Which is often when people add uv to "lock in" the terps, as ive seen it described. This is why many credit the philips CMH bulbs because they have been tailored to go into the UVA/B..

I mean dont stare into uv lights but if you're somewhere like I am extra vitamin D is always welcome.

Thanks for that LED05! I only just saw your post. You're right mate that sterilization band seems to be the one!

Im just probably going to have to get a UV meter going forward.

[Lost in a SOG]

Cant help but wonder myself if the benefits lie as much in killing airborne pathogens as the increase in terp synthasis.. especially sinxe they are there in the first place partly to help deter microbes.

Some research says ozone, o3, stimulates equal stress response to uvb in some plant species.