The Basics – Light provides the energy for life on earth.
What is the most critical factor for plants to thrive in your office? Having plant friendly lighting! Yes, foliage plants need the right amount of water, fertilizer, temperature control, insect control…. but without light none of that matters.
Plants are unique among all living organisms because they use the energy from light to produce the sugars, starches and additional substances needed to live. Light delivers the energy plants need to produce the food essential for growth and flowering.
The sun, of course, is the earth’s most important source of energy. Sunlight is comprised of the complete electromagnetic spectrum of light: Violet light, Indigo light, Blue light, Green light, Yellow light, Orange light, and Red light. (Known as ROGBIV)
What people see as being very intense bright light is the opposite of the bands of light that plants need to live. Human vision perceives light as brightest in the green and yellow area of the spectrum. Therefore, when we create lighting for homes, offices and other indoor environments, manufactures concentrate on the yellow / green bands rather than the red and blue areas of the spectrum. The human eye discernment of brightness throughout the light spectrum is opposite to the photosynthetic response of plants. So then the issue becomes what light works best for people and plants?
Clearly daylight is the superior light for people and plants, so a spot near a window is deal for both. The amount of light can be controlled by which way the window faces. North facing windows never get direct sunlight coming through them. East facing windows get morning sun. West facing windows have afternoon sun. South facing windows receive late morning, midday and early afternoon sun. The most natural light comes from a southwest facing window. Then consider if the light from the sun is blocked by trees, buildings, blinds, window coatings, etc.
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If artificial light is needed, Cool White LED’s or special lights made for plants are good options. For plants, the blue spectrum encourages leaf and stem development whereas red and orange bands encourage flowering. Fluorescent tubes can be made with added light from the blue and red spectrum. Metal-halide bulbs, when close to the plant, provide good lighting. Cool white LED lights work well because they have a lot blue spectrum light, in addition to being easily available, environmentally efficient, and comfortable to the human eye.
A Little More Detail
Lighting Measurement Terminology
Wattage is the quantity of electricity consumed by a light source
Lumens measure how much light you are getting. More lumens mean brighter light; fewer lumens means dimmer light.
Efficacy is the Lumens to watt ratio
* Watts measure the amount of energy required to light products. Lumens measure the amount of light produced.
Footcandles describe the amount of light that reaches the object
The major types of artificial lighting used in business and residential settings are a mix of incandescent, fluorescent, halogen, (HID) High Intensity Discharge and (LED) Light Emitting Diode. Unless the artificial light source is being purchased specially to light a living wall or highlight a specific plant feature, most lights are selected to meet the needs of office workers or customers. Remember that plants require the red and blue spectrum while people find light in the yellow and green spectrum most comfortable.
Plants are green because they contain the pigment chlorophyll. Chlorophyll absorbs light in the long red wavelength and the short blue wavelength sections of the visible light spectrum. Plants appear green because green light is reflected rather than absorbed. Plants need blue and red light for photosynthesis. Tropical plants – which are the type of plants that we use as indoor plants – are used to long days and short nights so 12-20 hours of light works well, but they do not usually want 24/7 lighting. Humans perceive light to be brightest in the green and yellow area of the spectrum. Since the human eye is particularly sensitive to green and yellow light, more weight is given to this region of the spectrum and the contributions from blue and red light are largely discounted. In lighting terminology, colors and light from the violet/blue end of the spectrum are referred to as “cool,” while those in the red/orange/yellow side are “warm”.
Incandescent bulbs are not good for plant growth. Although they emit a broad spectrum of light, it is heavily weighted towards red and infrared and lacking the blue spectrum. This makes plants soft and spindly. Additionally, if these light bulbs are close enough to produce significant light, they create too much heat for most plants.
Fluorescent tubes are a better choice for plants than incandescent or halogen bulb because they are efficient, do not produce much heat and are long lived. Since they are low cost, offices are often willing to add more lamps and /or wattage. This helps the plants counter light spectrum issues. Because people are most sensitive to green light, fluorescents peak sharply in the green area of the visible spectrum. The warm white adds a little red for the “warmer” appearance. If an internal coating of Calcium Halophosphate is added, the yellow spectrum is added to the tube. Fluorescent tubes are more suitable for plants than the incandescent or halogen bulbs. Consider using full spectrum, or “natural sunlight” fluorescent tubes since they emulate sunlight by emitting light in every spectral range or tubes coated with specialized phosphors designed for plants.
LED lights, unlike other artificial lights, can be made in different wavelengths. Plants grow differently depending on light wavelengths and not all plants have the same optimal wavelength. Standard cool white LED lights are designed to emit light heavily in the blue spectrum which is needed for foliage plant growth.
In conclusion, the best light for your plants is natural light. After that, look for lights that are heavy in the blue spectrum, have some red bands, are environmentally friendly, economically feasible, and comfortable to the human eye!
Sources:
https://www.hydrofarm.com/resources/articles/fluor_lights.php
https://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
http://www.ies.org/lighting/science/color.cfm
https://www.newprocontainers.com/blog/wp-content/uploads/LightingGuide2016-1.pdf
http://www.webexhibits.org/causesofcolor/7A.html