Plant lighting system with five wavelength-band light-emitting diodes providing photon flux density and mixing ratio control

Abstract

BackgroundPlant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED) technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses.ResultsWe have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD). The average photosynthetic PFD (PPFD) in the irradiated area was 438 micro-mol m–2 s–1 (coefficient of variation 9.6%), which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD) of 1 micro-mol m–2 s–1 nm–1 at every peak wavelength (405, 460, 630, 660, and 735 nm) grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength), the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg) and the blue-light SPFD gradient (micro-mol m–2 s–1 nm–1 m–1) was 2 deg per 1 micro-mol m–2 s–1 nm–1 m–1.ConclusionsThe plant lighting system, with a computer with a graphical user interface program, can control the PFD and mixing ratios of five wavelength-band lights. A highly uniform PFD distribution was achieved, although an intentionally distorted PFD gradient was also created. Phototropic responses of oat coleoptiles to the blue light gradient demonstrated the merit of fine controllability of this plant lighting system.

Response of Eustoma Leaf Phenotype and Photosynthetic Performance to LED Light Quality

“…A reduction in quantum efficiency (PSII) in the B LED-treated leaves may activate energy distribution in the photosystem, increase non-photochemical quenching (NPQ), and protect the leaf from LED-light injury [16,50]. In contrast, a lower rate of photosynthesis was found in R LED-treated leaves in lettuce [51], rice [52], and wheat [53]. Consequently, the lower rate of photosynthesis occurred due to low N-content of leaves under R LEDs with lower chlorophyll content [17].…”

“…Stomatal conductance (g s ), a photosynthesis parameter, is a bridge for gas exchange and water transpiration, and is significantly correlated with the light spectrum ( Figure 3) [53,55,56]. CO 2 diffuses through the leaf stomata to be used for photosynthesis.…”

The Impact of Spectral Composition of White LEDs on Spinach (Spinacia oleracea) Growth and Development

“…Some of the previous studies concluded that a controlled and tailored light spectral composition can be useful for inducing specific plant responses, and also for enhancing nutritional value in vegetables [19][20][21]. In [25] authors studied the effect of red plus three short-wavelength lights (near-UV, blue, and cyan) on lettuce and concluded that the optimal growth was obtained with red and blue treatment which caused a higher carbohydrate content; in fact about the 90% of light absorption by plant leaves is in the blue and red bands [26].…”

“…In [17], blue light influenced leaf morphogenesis, promoting differentiation of mesophyll cells and the formation of intercellular spaces, also having positive effects on leaf thickness and area. Light in the blue wavelengths promotes chloroplast development and increases net photosynthesis, the number of stomata and the thickness of leaves in cherry tomato plants [18]; blue light also induces a phototropic curvature of oat coleoptiles in the direction of light [19]. Even if the net CO 2 assimilation rate is reduced, rose growth under blue light alone presents a three-day slower, but more complete, vegetative and floral development [20].…”

Generating Selected Color using RGB, Auxiliary Lights, and Simplex Search

“…The pura e-mail: htkim@kitech.re.kr b e-mail: stkim@kitech.re.kr c e-mail: jongseok@kitech.re.kr d e-mail: kcjin@kitech.re.kr e e-mail: hskim@kitech.re.kr Figure 1. Concept of color selection and light mixing pose can involve improving the image quality, [10] determining optical spectrum, [11] and aiming desired color coordinate. [12] Commercial LEDs have typical colors.…”