Plants & light
Light is a source of energy and information for plants. It’s needed as energy in photosynthesis and it provides plants critical information about its environment, which the plant needs in order to germinate, grow to a certain size or shape, induce protective substances, flower and when to change from vegatative growth. Plants react to quality, intensity, duration and the direction of light.
In addition to the light visible to humans (400 nm – 700 nm) plants “see” or use other radiation too. The 400 nm–700 nm wavelength range is called “Photosynthetically Active Radiation” or PAR. Much of the light that plants need is in this range, but for optimal growth result, UV light (280 - 400 nm) and/or far-red light (700-800 nm) might be important. For example far-red is critical for the flowering of many plants. All light is not equal to plants, ie. some areas are more important than others.
Known photoreceptors are most efficient in the blue and red area of the spectrum. Green plants reflect a significant part of light in the green area of the light spectrum, while absorbing a higher percentage of blue and red light. The graph below shows the light spectrum of the sun on a cloudless day.
Much research has been conducted regarding the optimal light spectrum of plants. A good description of this is the Relative Quantum Efficiency curve for plants. It considers the photosynthetic rate of the plant (by measuring CO 2 uptake), the energy of light at different wavelengths and the plants absorption of light ie. what stays in the leaf and is not reflected away or transmitted through it. However, producing a plant which is sellable is not only about photosynthesis. Also other aspects like shape, flowering, color of leaves, color of flowers, taste, smell, root development, etc. are important to have a high quality plant.
Valoya Wide Spectra for Plants
The uniqueness of Valoya LEDs is the continuous spectrum of light. To get the desired impact from light, some areas of the light spectrum are suppressed and some are emphasized compared to sun light and the absorption curve of plants. The “right” spectrum for plants is strongly dependent on what the grower wants to achieve.
Valoya’s light spectrums are based on extensive research and testing, done in co-operation with leading research institutes, progressive and skilled customers and in-house. Valoya is continuously broadening its research to new plant species, different growing methods and new applications.
Valoya Growth Light Spectra
Valoya offers four main spectrum types in the R- and B-series products. Common features of the spectra All spectrums are continuous and range at least from 400nm to 700nm.
1) Valoya AP67 – General Growth Spectrum
For vegetative and generative growth. Performs very well with a large variety of plants, ranging from cucumber and tomato to lemon trees and even snow algae. It provides strong vegetative growth and early flowering of plants. With some leafy green plants elongation is achieved, while with some flowers the growth result is a compact plant. The AP67 spectrum has also been shown to promote quick and good rooting. The AP67 is strong on far-red (about 18 % of the total radiation) and has no UV radiation. Suggested use: Suitable for most vegetables e.g. cucumber, flowers and tree seedlings. Also positive results with algae. Appearance to humans: Pinkish light, quality control possible, good working environment.
2) Valoya AP673 – Growth Spectrum for Leafy Green Vegetables
AP673 is suitable for growing leafy green vegetables, herbs, micro-greens and other plants harvested before flowering. The AP673 spectrum produces high quality plants with balanced size, high fresh weight, good dry weight and strong color, aroma and taste. AP673 is modest on farred and has no UV. Suggested use: A general spectrum for leafy greens, herbs, micro-greens and cress, etc.. Appearance to humans: Peach-tone, quality control possible, good working environment.
3) NS2 – Compactness. Full Spectrum White
The NS 2 spectrum is a high intensity spectrum which accentuate plant compactness. The light output is balanced across the full visible spectrum and the green light area is not suppressed. The NS 2 is closest to the sun spectrum of Valoya’s spectrums. The NS 2 does not contain any far-red and has a few percentage of the light spectrum below 400 nm in the UV radiation area. Suggested use: The NS 2 spectrum is used to control elongation and to stress the plants to generate protective substances, which enhance taste or coloring of plants. Good for growth rooms where light conditions should resemble outdoor. Appearance to humans: White.
4) AP67S ARCH – Architectural Applications
The AP67S architectural spectrum is developed for usage in spaces where humans co-exist with plants. The spectrum includes additional green radiation in order to make the light white to the human eye. The spectrum is close to the absorption spectrum of many leafy green plants contributing to good growth and increased flowering. The spectrum includes no UV light. Suggested use: Plant walls, botanical gardens, rooms with humans and plants in the same space. Appearance to humans: Warm white. Note: This is not a common ‘warm white’ spectrum used in commercially available LED lights. It is a spectrum strongly related to the original AP67, thus very efficient in plant growth, yet human eye friendly.
Valoya has also other spectrums for special purposes, such as the Valoya G2 spectrum for speeding up vernalization and the Valoya Gold for tree seedling growth in multilayer environments. Valoya does not publish the light spectra of luminaires but the information is available for interested customers on request.
Bee friendly luminaires for greenhouses
Valoya has in a recent tomato trial demonstrated that the Valoya AP67 spectrum is also very beneficial to pollinating bees.
Bees are unable to navigate in a pure HPS light environment, so bee hives are not opened until sun light is available. This shortens the working time for the bees significantly during winter. Under the Valoya AP67 lights, bees start to operate immediately when the lights are switched on, even during night and no sun light conditions. Valoya AP67 thus improves the pollination of the flowers. In addition to this, Valoya LEDs are significantly cooler than HPS fixture and hence do not kill the bees, when they come close to the light fixtures.
Producing high quality plants with LED lighting
To produce a high quality plant, it is not enough to use just red and blue light typically found in conventional horticultural LEDs. The same applies for High Pressure Sodium lights, which are dominantly yellow.
A good balanced ratio between red and blue light, needs to be complemented with far-red and green in right proportions for the right applications. For example far-red, 700–800 nm is critical for flowering of many plants. Less is known about the green, 500–600 nm area, but recent research is finally able to conclude that this is also important for plant development. Besides being potentially harmful, plants also show photomorphogenic responses to UV-B (280-315 nm) radiation. Both UV-B and UV-A (315-400 nm) radiation are important in inducing production of phenolics, anthocyanins (coloration) and antioxidants in plants. Thus the full spectrum from about 350–750 nm at a suitable light intensity is interesting in plant cultivation. The key is then to create a light which is optimally suitable for its task, by balancing the different areas so that the plant gets the right energy and signals to achieve the growers’ goals.