SEED OF AN IDEA

Iain Carlile finds that plant cultivation is among the key topics in the latest Lighting Research and Technology papers (a)

Photomorphogenesis of wheat sprouts

(b)

an et al’s paper examines the use of LED lighting in plant growth and development, specifically, wheat sprouts. Experiments were undertaken using varying photosynthetic photon flux densities with a continuous spectrum of light. The result of the experiments was that an optimum photosynthetic photon flux density was identified. This may enable a reduction of irradiance during early development of cultivated plants with no harm caused to the plant, while lowering the energy consumption required for cultivation.

Also considering the growth of plants, Degni et al’s paper looks at the impact of the light spectrum and photosynthetic photon flux density of LEDs on the germination and seedling emergence of okra. The light spectra used in the experiments had peaks in the red, blue or green regions of the visible spectrum. The authors noted that there were significant interactions between light spectrum and photosynthetic photon flux density on the mean germination time, germination rate, uncertainty of germination, and seedling emergence height. The spectrum peaking in the red showed a better germination rate and less uncertainty than the spectra peaking in the blue or green parts of the visible spectrum. The varying photosynthetic photon flux also affected the seedling emergence height.

Investigating the influences of light on the circadian system, Truong et al developed a computational model of circadian stimulus, using photometric and colourimetric quantities, rather than spectral power distribution (SPD).

The computational model uses simple parameters of illuminance and the chromaticity coordinates of the white light source. Validations of the computational model were undertaken, demonstrating a good fit with Rea’s quantity CS 2018 results for circadian-effective light on humans, with acceptable errors for white light sources, in the illuminance range of 10-10,000 lux. This therefore provides a relatively simple formula. Bao et al conducted an experiment on 24 young adults with myopia in both eyes and equal refractive power. The subjects undertook a reading task of Chinese text under varying illuminance conditions (3, 30, 300 and 600 lux) and text contrast (95 per cent and 45 per cent). During the experiment measurements were taken of the subjects' reading distance, angle of head tilt, and reading speed.

The results showed that the subjects tended to shorten their reading distance and increase their head tilt angle when reading at low illuminance, and further, reading speed was notably slower at low illuminance and low contrast. The observed effects were found under both of the text contrast levels that were tested, but were more pronounced at the lower contrast. It was found that an illuminance of 300 lux or greater, coupled with high contrast text, facilitated good reading posture and rapid reading of the Chinese text among all of the subjects. Iain Carlile FSLL is the immediate past president of the SLL and a senior associate at dpa lighting consultants  Specialised irradiation unit for wheat sprouts (Han et al) H

Lighting Research and Technology: OnlineFirst In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online. SLL members can gain access to these papers via the SLL website (www.sll.org.uk) Circadian stimulus – A computation model with photometric and colorimetric quantities W Truong, V Trinh and TQ Khanh Photomorphogenesis of wheat sprouts with LED irradiation of different intensities T Han, T Astafurova, S Turanov, A Burenina, A Butenkova, E Surnina and D Valiev Impact of light spectrum and photosynthetic photon flux density on the germination and seedling emergence of Okra BF Degni, CT Haba, WG Dibi, YA Gbogbo and NU Niangoran Effects of illuminance and contrast on the reading of Chinese text by myopes J Bao, R Tan, J Huo, B Drobe and H Chen Power supply (c) (d) Driver Electrical current (A), voltage (V) LEDs Lights control

RD 485 Power supply Climate control Temperature Humidity PPFD Sensors

700600500400 0 49 128 192 260 µmol·m –2 ·S –1 40 20 Irradiance, mW/m 2 0

Wavelengh, nm Temperature Humidity Watering CO 2

CO 2 Communication unit Figure 1. (a) Block diagram of the control system; (b) picture of the ‘‘Phytotron’’ greenhouse; (c) specialized irradiation unit; (d) spectrum of the LED irradiation system