Light Sources Needed by Plants

Do you know what lights are suitable to plant growth?

Photosynthesis and light

Different wavelength sensitivity between human and plants

Light plays a critical role in the growth, development, blossoming, and fruit bearing of plants. Because plants' response to light spectrum has different characteristics from that of human eyes, light for plants is measured in different units.
The sensibility of human eyes varies by the wavelength and colour of light - highest to green light with the wavelength of 555nm and lower at any other wavelength that is either longer or shorter. Lumen (lm) and lux (lx) are the units of luminous flux and illumination. They are based on the vision of human eyes.
Plants are sensitive to blue and red lights. The following figure shows the absorption spectrum of plant leaves. In the measurement of plants, photosynthetic photon quanta flux density (PPFD) is usually used to evaluate how lighting affects plant leaves in photosynthesis. Its unit is μmol/m2/s.

Lights that are bright for human may not be so for plants.

Lumen (lm) and illumination (lx) are the units that are based on the relative luminous efficiency of human. They cannot reflect effective light intensity for plant cultivation.

Relative luminous efficiency of human

Absorption spectrum of plant leaves

(* Source: Mr. Goto, Graduate School of National University Corporation Chiba University)

Lights Needed by Plants

Some Thoughts on Light Spectrum

Emphasis on cultivation efficiencyRed + Blue
Emphasis on operability and universalityWhite
Emphasis on balance among cultivation efficiency, operability and universalityRed + White

Intensity of illumination is dependent on the number, output power, and illuminating distance of lamps deployed on the illuminated area.

About LED Luminance

Proposals are mostly submitted to customers in terms of luminance for cultivation (PPFD or PFD) If any data about Photon Flux is required, customers will design their optical systems by themselves (luminous intensity distribution may also be required) It is also important to determine how many LEDs of what power for each are required to cast necessary luminance to a certain area.

The angle of illumination may be selected using reflectors.
If an inappropriate angle of illumination is selected, the illumination will not be distributed evenly, thereby resulting in difference in plant cultivation.

Light and PPFD

Photon flux

Light, by nature, is not only waves but also particles. Each of these particles is called a photon. The number of photons released from a light source in a certain direction is expressed in μmol/s.

Photon flux density (PFD)

The number of aforesaid photons reaching a certain area within a certain time period is called photon flux density, which is expressed in μmol/m2/s.

Photosynthetic photon flux density (PPFD)

Photosynthetic photon flux density (PPFD) is referred to as the aforesaid PFD within 400-700nm, the only range of wavelength that is usable by photosynthesis.

Varied Agricultural Forms

Combination of solar and artificial light

Combination of solar and artificial light

Cultivation in glass greenhouses, PVC greenhouses, or other semi-artificial environments


Full-artificial lighting

Artificial cultivation in rooms that are fully isolated from outdoors