Light is essential for both humans and plants, but they interact with and benefit from it in vastly different ways. Whilst designing lighting solutions for different needs requires a key understanding of the differences, could there also be some types of lighting that benefit both plants and humans?
Here we outline the must-know differences between the biology and science of horticultural lighting and general lighting.
The Purpose of Light – Is It for Vision, or Growth?
Plants get the energy they need to photosynthesize and thus grow from light. Light travels as photons, which the plant receives through chlorophyll and other pigments. In photosynthesis, the plant converts the energy transmitted by the photons into a chemical form that enables water, carbon dioxide and minerals to be converted into oxygen and biomass.
In addition to growth, plants use light to observe their environment. In nature, changes in the amount and quality of light received can signal, for example, about other plants that are competing for light, in which case the plant begins to use its energy for stem growth and faster flowering.
For people, light primarily serves two roles: it enables vision and regulates circadian rhythms, our body’s internal clock that dictates sleep, alertness, and mood. Humans need light, especially natural sunlight, to stimulate vitamin D production, which supports bone health and immune function.
Are Plants and Humans on the Same Wavelength?
Plant photosynthesis is driven primarily by blue (400–500 nm) and red (600–700 nm) wavelengths. Green light, the colour we see most vividly, is reflected more off leaves in comparison to other wavelengths of light, which is why they appear green to us.
Interestingly, most green light (500-600nm) is actually absorbed or transmitted through plant leaves (around 85%). The reason that plants and their leaves appear so green to us, is because green wavelengths are reflected more in comparison to other wavelengths of light which are visible to humans.
The light outside of photosynthetically active radiation (400–700 nm) also affects plants. Strong short wavelength radiation in blue and UV regions often results in accelerated secondary metabolite production as the plant aims to protect itself from potential damage. The longer wavelengths in far-red region (700-800nm) are important for environmental signals, which can regulate flowering and stem elongation in plants.
Humans require full-spectrum visible light for optimal vision, with a particular sensitivity to blue light (in the specific blue wavelengths around 460–490 nm), which plays a role in regulating sleep patterns. Excessive exposure to artificial blue light (from screens, for example) can disrupt sleep, but a balanced exposure to blue wavelengths during daylight hours can enhance alertness.
Lux, Lumens, Watts and Micromoles- Which is Correct?
The quantity and quality of light can be described in many ways, so it is important to choose a suitable unit when comparing light properties. Full-spectrum light designed for plant production can look the same to the human eye as the light produced by general lighting installed in an office, although the spectrum distribution of these may be quite different.
For Designing Light Plans Catered to Humans:
Light intensity can be measured in many ways, and in general lighting, e.g. lumens, lux and candelas are being used. A lumen is a unit of luminous flux that measures the amount of light. One lumen is approximately the light produced by one candle in an area of 30 x 30 cm from 30 cm distance.
Luxes also take into account the surface area on which the light falls: If an area of one square meter is illuminated with a luminous flux of one lumen, we speak of lighting of one lux.
Candela considers the shape and extent of the light beam, so for example a spotlight with a narrow light beam produces more candelas than a lighting panel illuminating a wide area, even if the light flux is the same.
A watt is a unit of power, and one watt corresponds to one joule of energy per second. Therefore, using watts to describe the quantity of light is not recommended, watts should be used to describe the power that the light source uses.
For D lighting Plans Which Cater to Plants:
In plant lighting, the most practical way to express light intensity is the amount of photosynthetically active radiation (PAR) in micromoles per second per square meter (µmol/m2/s), which is the intensity of the light that is essential for plant photosynthesis.
PAR given in µmol/m2/s is also referred to as PPFD (photosynthetic photon flux density), whereas PFD refers to just photon flux density and includes wavelengths of light outside the PAR region.
For answering to the lighting needs of plants and humans in the most optimal way is to have a quality broad spectrum with high colour rendering index. This ensures that the plants receive all necessary wavelengths of light for enhanced growth and allows humans to inspect the true colours of the plant, which is impossible under lighting that only consists of red and blue radiation.
Products of our two brands, Valoya for research based horticultural lighting and GreenluxLIGHT for quality general lights are designed and manufactured under the same roof by a team that understands the needs of plants and humans alike.
Our optimized sunlight spectrum Solray385 divided in wavelength regions of UV (100 – 400 nm), PAR (400 – 700 nm), Far-red (700 – 800 nm) and typical human vision region (380 – 750 nm).
