The lighting for plants. The lighting for humans.
Vertical greenery or green walls have become a part of our interiors. They make our homes, offices, and shops more attractive, but we also feel better in their environment. They purify the air and absorb CO2, reduce ambient noises, regulate the temperature in the room, and humidify the air. Indirectly, our stress level and, surprisingly, as well sick leaves of employees are decreased and opposite, productivity, a feeling of well-being and connection with nature are improved significantly.
But of course, a living wall requires maintenance – proper nutrition, fertilization, watering, and illumination – to keep plants green and fresh and avoid overgrowth or flowering when it is not required. For an internal living wall to thrive long term, it is essential to get the correct balance of both intensity and spectrum of lighting and, on the other hand, to guarantee the illumination comfortable for humans means to provide a hybrid light-spectrum optimized for photosynthesis in any environment. To choose the most suitable ratio, we need to understand how plants react to different light and as well what is the human perception of different wavelengths.
The reaction of plants and humans on different spectrums.
Regardless of whether the color of the light is red or purple, the plant will absorb some energy from it and react accordingly. Green lighting is the least effective for plants because they are also green due to the pigment chlorophyll. Blue light (referred to as radiation with wavelengths between 400-500nm) is necessary, at least in a minimal amount, to sustain normal vegetation development because it regulates the opening of stomata on leaves that control the uptake of carbon dioxide and water loss. In combination with other light spectrums, wavebands promote flora compactness, production of secondary metabolites, root development, and increase chlorophyll accumulation, so in general, the light improves overall plant health and indirectly improves flavor, aroma, or taste. It also increases the amount of antioxidants that the green wall produces.
Violet or purple light has a shorter wavelength and a higher amount of energy. When you expose plants to purple or violet color, they grow faster, have a better aroma, and the vegetables and fruit taste richer. For that reason, the combination of red and blue full light spectrum is used in greenhouse farming to boost growth and promote healthier blooms. Human perception of blue light (especially at shorter wavelengths between 400-425nm) is low compared to green light. Blue light is equally effective as green or red light at driving photosynthesis, which means that even if it appears dim to us, it is helpful for plants. So in easy terms, what has a significant impact on plants, people do not realize, and therefore the blue light in the standard light sources can make a difference when it comes to green walls, and it gives a basis for a hybrid light source.
Which amount of the blue spectrum is suitable for living walls?
Green walls do not require fast-growing plants, and the accent is to keep them growing slowly and with a dense surface. How to regulate blue light accordingly? The recent research done at Michigan State University (pic. 1) shows the amount of blue light and its influence on the plant growth and size of the leaves. Blue light spectrum suppresses extension growth plants grown with blue light are usually shorter and have smaller, thicker, and darker green leaves than plants grown without blue light.
Pic. 1 Seedlings grown indoors with blue light are often shorter and have smaller leaves than those grown under only red lights. Plants grew at the same photosynthetic photon flux density (PPFD) in an environmental growth chamber.
(Research from Heidi Lindberg and Erik Runkle, Michigan State University, source: https://www.sciencedirect.com/science/article/abs/pii/S0098847219311499)
If we wish to maintain plants in the interior without unwanted growing, we must provide them with at least 50% blue light compared to red light. The absence of blue light can cause fast-growing plants with large leaves. Further research shows as well that blue light does not regulate flowering at low light intensities (<30 μmol·m-2·s-1), in comparison, higher intensity of blue light (>30 μmol·m-2·s-1) can inhibit or promote flowering in daylength-sensitive crops, so for green walls is considered as the optimized solution to have a moderate amount of blue light if the aim is not to achieve flowering.
Radiation with shorter wavelengths (blue/UV) stimulates the production of compounds that can influence leaf coloration. For example, in the absence of blue/UV radiation, plants that have purplish leaves outdoors may have green leaves.
Summary and recommendation.
In summary, it seems the best for indoor plants is to have a moderate amount of blue light and a spectrum that is the most similar full sun spectrum. This light source, which simulates this full sun spectrum, can be installed in any track or downlight lighting fixture from the Light4U BV range. Pic. 2 shows the difference between the standard 4000K and Light4U Spectral – full spectrum 4000K.
Pic. 2 Average Spectral Difference (ASD) standard 4000K vs Light4U full spectrum 4000K comparison.
While the typical 4000K solution brings too much blue light in a specific wavelength (450-470nm) more than other spectrums, the full spectrum LED achieves 4000K by a more comprehensive light spectrum (already from the visible 400nm). The Light4U full spectrum has a higher portion of the red color that supports root health, better absorption of nutrition, and increasing chlorophyll accumulation. By this approach, the light spectrum is the most similar to the sun spectrum in the morning (4000K). (pic. 3).
Pic. 3 Comparison of Average Spectral Difference (ASD) between several light sources at 4000K.
The Light4U Spectral improves our indoor experiences under artificial lighting with its vivid color rendering and simulating full sun spectrum, combining human-centric lighting with natural light for plants. Light4U Spectral, or full-spectrum, brings full-spectrum natural light indoors. Target applications include office, education, healthcare, retail, hospitality, museums, and residential lighting, everywhere where it is required to improve living creature well-being for humans and plants.
Need lighting for your living green wall? Feel free to contact us; we are happy to help.