Valoya Research Team
The rapid increase in the use of LED technology for horticultural lighting applications has also raised discussions regarding the potential human health risks compared to legacy lighting solutions. This is somewhat due to the differences in visual appearance (colour and intensities) of the light in such applications.
At a high enough intensity, any type of light, regardless of the source has the potential to harm the eyes or skin through prolonged thermal exposure or photochemical effects of ultraviolet, blue light &/or infrared emissions. Shorter wavelength, higher energy blue light (400nm and 500nm) can cause retina damage through a combination of photochemical action and high intensity. Higher concentration light sources will provide more direct energy and a higher risk. For example, staring at a clear blue sky (scattered blue light) is a low risk, while looking directly at the sun can begin irreversible damage almost immediately.
Prolonged direct viewing of bright light sources must always be avoided, especially at short distances. In practice, nobody voluntarily spends any significant time looking directly at an intense light source. Common sense and the natural human instinctive aversion reaction (we instinctively shut our eyes or look away) means that prolonged direct exposure of the eye to a potentially damaging light source will be avoided.
Like other lighting technologies, LED grow lights must be checked for photobiological safety according to EN 62471 – the standard for photobiological safety of lamps and lamp systems. This includes thermal and blue light analysis in the spectral range is 200nm to 3000nm. EN 62471 exposure limit classifications represent conditions under which it is believed most people may be repeatedly exposed without adverse health effects. It should be noted that the classification only indicates potential risk. Depending upon use, the risk may not actually become a real hazard.
When it comes to human visual perception, what is often forgotten is that “traditional” light sources were never designed or intended specifically for horticulture applications. Historically, artificial light has always been optimised for human visual benefit. LED grow lights on the other hand are specifically designed for the benefit of plants and thus sometimes appear strange to human eyes. Valoya LED grow lights are true wide spectrum lights, meaning they contain bits of all colours from the spectrum, including outside the PAR area, just like the sun. Because of this they appear from white to soft pink which makes them pleasant to work under and makes identifying the colour of plants underneath them easy. A cheap alternative to that, which most LED manufacturers opt for, is using red, blue and white LED chips which result in a strong, piercing pink color, unpleasant to human eyes. In terms of health effects, Valoya LED grow lights are not blue dominant and are classified in the no-risk or lowest risk group.
The eye is a complex organ that naturally tries its best to compensate for varying lighting conditions, and LED grow light spectra may not always appear “natural” to humans. If lighting conditions for the human eye change (e.g. going from a LED lit growth environment to natural daylight), colour perception may be temporarily affected while the eye adjusts. This is natural and should not be misinterpreted as possible “damage” from exposure to LED light.
In conclusion it can be said that commercially available LED light sources (for horticultural or other applications) can be considered human safe when designed, installed and used in accordance with the applicable standards, regulations and manufacturer’s instructions. Overall, in terms of photobiological safety, LED grow lights have similar characteristics to those of any other lighting technology.
David Israel, a PhD. Student from the Univeristy of Helsinki, is studying the role of aquaporins in plant water relations through the hydraulic architecture and the control of water loss. The aim of this experiment is to study water transport through the plant in general, but also the impact of alterations in water transport on plant development and water use efficiency. Water relations are measured by monitoring the gas exchange in a leaf with specific equipment. In the picture below, the measuring is taking place. As you can see, the plants have been potted higher than normally, in order for the machine to have a better access to the leaves. Like many researchers today, David is also using the model plant, Arabidopsis thaliana, in his experiments. Arabidopsis thaliana plants of different developmental stages are growing under the Valoya AP67 grow light spectrum.
This study is being conducted in the University of Helsinki, Department of Biosciences. David Israel is part of the Canopy spectral ecology and Ecophysiology group, led by Matthew Robson.
Characterizing spectral properties and calculating irradiances are everyday tasks for many researchers in the field of plant photobiology. Varying waveband definitions in use, different photoreceptors found in plants, let alone the difference between expressing light on photon or energy basis can make one’s head spin. To tackle this, a couple of publications and an application are highly recommendable.
Starting from nature of light and its interaction with matter, going through biological light perception and regulation and evolution of photosynthesis; all this and a myriad of another topics, can all be found in the latest edition of ”Photobiology: Science of Life and Light” (edited by Lars Olof Björn).
Beyond the Visible: A handbook of best practice in plant UV photobiology (edited by Pedro J. Aphalo et al.) offers a knowledge base for methods for research on the responses of plants to ultraviolet radiation, dealing with experimentation on ecological, eco-physiological and physiological questions (practical recommendations for obtaining reliable and relevant data and interpretations can be applied beyond UV!).
Then for the application: Have you ever been wondering how nice it would be to easily maneuver between the energy irradiance (W m-2) and photon irradiance (mol m-2 s-1) calculations? Or how to calculate spectral properties quickly, check the R:FR ratio etc. Or how to easily determine doses that are especially important when doing experiments with supplemental UV-B radiation? Creating informative graphs, highlighting wavebands? Well look no further, Photobiology packages for R, compiled by Pedro J. Aphalo, are here. The packages are documented in pedantic detail and user guides give ample instructions and examples. Please see below an example graph of sun spectrum and annotations for selected wavebands (UV-B and UV-A according to ISO, far-red according to Sellaro et al.).
ISO (2007) Space environment (natural and artificial) - Process for determining solar irradiances. ISO Standard 21348. ISO, Geneva.
ISO/CIE 17166:1999, Erythema reference action spectrum and standard erythema dose.
Sellaro, R., Crepy, M., Trupkin, S. A., Karayekov, E., Buchovsky, A. S., Rossi, C., & Casal, J. J. (2010). Cryptochrome as a sensor of the blue/green ratio of natural radiation in Arabidopsis. Plant Physiology, 154(1), 401-409. doi:10.1104/pp.110.160820.
Plant growth and morphology can be modified with light quality, but could plant pests be affected too? For example narrow bandwidth UV-B light can be used directly and efficiently against the growth of powdery mildew fungi, as thorough investigations in a collaborative project by Cornell researchers and colleagues in Norway have shown. However, the UV-B treatments must be applied at night, so that the wavelengths in natural light can’t repair the damage caused by UV-B light to powdery mildew genome.
Aphids are a tricky problem in lettuce, hiding between the leaves. There they are protected against chemical pesticides as well as natural enemies used against aphids. Aphids can be thwarted with systemic pesticides, that are transported in plant vascular tissues and foliage. But fresh edible plants would be safer, if pests could be under control without pesticides. There would be no need to worry about waiting periods or anyone exposed to chemicals during their use.
In recent experiments done by Irene Vänninen at the Natural Resources Institute Finland, aphid reproduction rate (glasshouse-potato aphids Aulacorthum solani) was monitored on iceberg lettuce seedlings grown under different spectra for three weeks. In all, conditions were good for the aphids, that multiplied their numbers. At the same time, plant growth performance remained on a good level as well, as was demonstrated by plant dry weight, that was not reduced due to the aphids. Detailed analysis of the results is ongoing and it is clear that both direct and indirect effects (through production of plant protective compounds) of light quality will remain an interesting field of study in controlled environment pest management.
Photos by Ari Eskola, LUKE.
Jarmo Holopainen, Professor of Applied Ecology from the University of Eastern Finland, Department of Environmental Science and his research group are doing multifaceted biological and ecological research. The research is related to biological and ecological effects of global change, plant-herbivore interactions, secondary chemistry of plants, biogenic volatile organic compounds and to formation and ecological effects of biogenic secondary organic aerosols. Recent publications range from defence pathways in Scots pine bark after feeding by pine weevil and biotic stress accelerating reactive emission of biogenic volatile compounds leading formation of climate-relevant aerosols in boreal forests, to plant-to-plant communication with volatile defence compounds.
Recently installed Valoya lights are used to e.g. study the effects of light quality on plant growth, production of phenolic and terpenoid compunds and fine structure of the plants. These pilot experiments are related to a project assessing the possibilities to use modulation of light spectrum for enrichment of secondary metabolites in plants.
Broccoli plants growing under Valoya lights at the University of Eastern Finland.
During the past two weeks I've enjoyed full sunshine, though accompanied by a bit different temperatures, in two continents. First I attended to the LED symposium at the The University of Arizona - CEAC in Tucson (US). All the latest results and ideas presented are available as pdf-files through the event website.
Another meeting was the 50th Horticultural Science Conference in Freising-Weihenstephan (Germany), organized by the Technical University of Munich and the University Weihenstephan-Triesdorf. Topics varied from production of bioactive compounds in carrot, to searching downy mildew resistant basil genotypes and to comparing light spectra in vitro cultivation of ornamental plants: you are encouraged to browse through the book of abstracts.
Valoya B-series with AP673 spectrum used in an experiment with basil and parsley.
Researchers at the Agrifood Research Finland MTT have done a set of interesting rooting experiments with different growth substrates and varying light conditions. Plum variety “Sinikka”, cloudberry “Nyby” and saskatoon “Martin” were rooted either on peat or sphagnum moss based substrates. Valoya AP67, traditional red&blue LEDs and high pressure sodium (HPS) were used as light treatments.
Saskatoons and cloudberries rooting under Valoya AP67 (all pictures by MTT).
Differences in cloudberry seedlings quality were largest between the growth substrates, but some differences between light treatments were also observed, please see the graph below.
On left cloudberry seedlings grown in sphagnum moss, on right in peat, both under Valoya AP67.
Survival of the saskatoon seedlings was low, regardless of light treatment or growth substrate, hence no conclusions were made based on this experiment.
Concerning plums, differences in the number of leaves and fresh weight were subtle between the light treatments. Under red&blue LEDs the seedlings were shortest. Researchers concluded that choice of appropriate light quality depends on the target: After the rooting and adaptation phase the number of survived seedlings was highest under Valoya AP67, and plants clearly benefitted from the lower temperature in the plastic growth cubicle, but during the last weeks of continued growing period the plants seemed to benefit from the directional heat emitted by the HPS lights. If formation of side shoots of small seedlings after the adaptation phase is considered to be less desirable, under Valoya AP67 the number of side shoots was lowest and under HPS the number of side shoots was highest.
Plum seedlings after 3 weeks of rooting and adaptation phase. Left Valoya AP67, middle red&blue LEDs, right HPS.
MTT CustomerSolutions provides research, consulting, testing and development services for corporate and public-sector on agricultural and food industry.
Stemming from my background in studies concerning plant responses to UV radiation, I wanted to highlight the news about the recovery of the ozone layer. Please take a look at the article After 30 years of protecting the ozone layer, some reasons to be cheerful, written by Nigel Paul, Professor of Plant Science at the Lancaster University and co-chair of the United Nations Environment Programme (UNEP) panel on ozone depletion.
During the days of most extensive research related to ozone depletion and increasing levels of UV-B radiation, mainly the harmful effects were considered. Nowadays UV studies have taken great steps forward, looking beyond ozone depletion. Recently the UV-B induced morphological effects have been elucidated and e.g. the need for understanding of the UV-B dose–response underpinning morphogenesis was demonstrated by Matthew Robson et al. in the review Re-interpreting plant morphological responses to UV-B radiation. Jason Wargent and Brian Jordan summarize the multifaceted roles of UV-B radiation in their review From ozone depletion to agriculture: understanding the role of UV radiation in sustainable crop production: “Indeed, it could be argued that UV radiation acts as a ubiquitous, albeit energetic, cue in the regulation of typical plant development, as opposed to a consistent inducer of damage”.
Attention has been drawn also to the definition of photosynthetically active radiation (PAR) itself. Commonly accepted definition is 400-700nm, challenged with good reason by Turnbull et al. Photosynthetic beneﬁts of ultraviolet-A to Pimelea ligustrina, a woody shrub of sub-alpine Australia. Opposite end of the spectrum needs to be considered here too, as demonstrated by Pettai et al. The long-wavelength limit of plant photosynthesis, measuring a detectable O2 evolution remaining till 780 nm in sunflower leaves. Using the current PAR limits may lead to underestimation of photosynthetic carbon gain, as pointed out by Turnbull et al., that in turn can affect the outcome of climate change scenarios through source-sink estimations!
Picture above shows sun spectral energy irradiance reaching ground, highlighting different wavebands (UV-B 280-315nm, UV-A 315-400nm, PAR 400-700nm, far-red 700-750nm). Picture drawn with R, using photobiology packages developed by Pedro J. Aphalo.
And finally, despite the promising news about the recovery, ozone depletion can not yet be overlooked. This is demonstrated by Williamson et al., emphasizing the interactions between the drivers of climate change and ozone depletion, and the feedbacks among climate, ozone and UV: Solar ultraviolet radiation in a changing climate.
Docent Matthew Robson and his research group (Canopy Spectral Ecology and Ecophysiology, CanSEE) are continuing with their work presented in this blog last year (see post “At the crossroads”). Current experiments in a growth room, exploring the mechanisms of response to canopy shade during spring and summer, focus on plants’ perception and use of spectral signals during germination and establishment. Various plant species are grown under Valoya AP67 spectrum, or under the AP67 spectrum equipped with a filter removing blue wavelengths and additionally one side of each compartment is supplied with UV-B radiation.
Matthew Robson and his student Paulina Mastalerz monitoring the experiment in the growth room.
In addition, experiments at the University of Helsinki greenhouse aim to elucidate further the signals that plants receive and process and the consequences of these responses for the environment. Plants are grown under different Valoya lights and one side of the compartment is supplied with UV-B radiation.
Wild wood sorrel (Oxalis acetosella) from the forests around Helsinki and a garden cultivar rich in anthocyanins are grown under three types of Valoya spectra in Viikki greenhouse at Helsinki University under simulations of forest shade enriched and depleted in specific parts of the solar spectrum. The growth, development and physiological responses of the plants are monitored.
SenPEP is a research group led by Dr. Pedro J. Aphalo. Based at the University of Helsinki, the group’s field of research is sensory photobiology and ecophysiology of plants. In more detail, the group studies e.g. the modulation of the light sensitivity of stomata by other environmental factors, effects of natural UV radiation on plants and via plants on other trophic levels. Another aspect of their research is how to utilize photobiological knowledge in horticultural practise. Regarding this topic, Valoya and SenPEP research group have been collaborating for some years now.
The special edition of Projects Magazine (Insight Publishers) “Finland – Flying the flag for research excellence”, introduces varying research fields and topics, from owls and black holes to aforementioned sensory responses of plants and SenPEP (pages 42-44).
Picture below showing (from left) PhD student Sari Siipola, yours truly, and Valoya's Research & Solution Manager Stiina Kotiranta at the University of Helsinki greenhouse in Viikki, sampling begonias at the end of the experiment.