Sunlight serves as the primary electromagnetic energy source for terrestrial ecosystems, driving the photochemical reactions required for plant growth and development. From a physical perspective, solar radiation consists of electromagnetic waves that travel through the vacuum of space at the speed of light, reaching the Earth’s surface in approximately eight minutes (Okun, 2009; Hartmann, 2016). When sunlight reaches plants, their leaves absorb the light and convert it into chemical energy through photosynthesis (Taiz et al., 2015).

Although sunlight appears as a continuous radiating white spectrum, it is composed of photons with discrete energies corresponding to different wavelengths. The effectiveness of this radiation is determined by its spectral quality, particularly within the Photosynthetically Active Radiation (PAR) region (McCree, 1972). Plants exhibit high relative quantum efficiency under red light, which is considered one of the most effective wavelengths for driving photosynthesis, while blue light is slightly less efficient but still plays an important role in plant physiological processes (Bian et al., 2018). These wavelengths are selectively absorbed by chlorophyll pigments to initiate electron transport during photosynthesis (Taiz et al., 2015). In contrast, green light is often reflected or transmitted deeper into leaf tissues, contributing to improved light penetration and more uniform photosynthetic activity within the plant canopy (Liu & van Iersel, 2021).

Beyond energy production, light also functions as an environmental signal regulating plant growth through photomorphogenesis. One well-known response is phototropism, the directional growth of plants toward a light source caused by uneven light distribution (Orbović & Poff, 1993). This gradient of light leads to the redistribution of growth hormones such as auxin, resulting in increased cell elongation on the shaded side of the plant and causing the shoot to bend toward the light (Sullivan et al., 2013). In addition, solar radiation contributes thermal energy through infrared wavelengths, which must be carefully managed to avoid heat stress in crops. Agricultural practices such as shading systems, greenhouse design, and controlled ventilation are therefore used to regulate temperature and maintain optimal physiological conditions for plant metabolism (Ahmed et al., 2017; Boulard & Wang, 2000).

Modern agriculture increasingly applies these physical principles through the optimization of LED lighting technologies (Kusuma et al., 2020). Unlike conventional broad spectrum lighting sources, LEDs can be engineered to emit specific spectral outputs, primarily red and blue wavelengths, to enhance photosynthetic efficiency while reducing energy consumption (Bian et al., 2018). The performance of these devices is governed by semiconductor physics, particularly the band gap energy (Eg) of the materials used. Electron transitions between the valence band and conduction band determine the wavelength of emitted light (Sze & Ng, 2007). By integrating these physical insights with plant science, researchers can design controlled lighting environments that enhance crop productivity while promoting sustainable and energy efficient food production (Kusuma et al., 2020).

References
1. Okun, L. B. (2009). Photon: The history of a concept. Physics Today, 62(10), 34–39.
https://doi.org/10.1063/1.3248474

2. Hartmann, D. L. (2016). Global Physical Climatology (2nd ed.). Academic Press.

3. Taiz, L., Zeiger, E., Møller, I. M., & Murphy, A. (2015). Plant Physiology and Development (6th ed.). Sinauer Associates.

4. McCree, K. J. (1972). The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agricultural Meteorology, 9, 191–216. https://doi.org/10.1016/0002-1571(71)90022-7

5. Singh, D., Basu, C., Meinhardt-Wollweber, M., & Roth, B. (2015). LEDs for energy efficient greenhouse lighting. Renewable and Sustainable Energy Reviews, 49, 139–147.
https://doi.org/10.1016/j.rser.2015.04.117

6. Liu, B., & van Iersel, M. W. (2021). Green light improves photosynthetic performance and plant growth under controlled environments. Environmental and Experimental Botany, 182, 104305. https://doi.org/10.1016/j.envexpbot.2020.104305

7. Orbović, V., & Poff, K. L. (1993). Phototropic response of Arabidopsis thaliana seedlings. Plant Physiology, 102(3), 1039–1043.

8. Sullivan, S., Thomson, C. E., Kaiserli, E., & Christie, J. M. (2013). Interaction of phototropins with AUX/IAA proteins regulates phototropism. Proceedings of the National Academy of Sciences, 110(40), 16367–16372. https://doi.org/10.1073/pnas.1308507110

9. Ahmed, H. A., Tong, Y., Yang, Q., Alagarasan, G., & Li, X. (2017). LED lighting for improving plant growth, development, and secondary metabolite production. Horticulture Research, 4, 17014. https://doi.org/10.1038/hortres.2017.14

10. Boulard, T., & Wang, S. (2000). Greenhouse crop transpiration simulation from external climate conditions. Agricultural and Forest Meteorology, 100(1), 25–34. https://doi.org/10.1016/S0168-1923(99)00082-9

11. Kusuma, P., Pattison, P. M., Bugbee, B., & van Iersel, M. W. (2020). From physics to fixtures to food: Current and potential LED efficacy in horticulture. Horticulture Research, 7, 56. https://doi.org/10.1038/s41438-020-0283-7

12. Bian, Z., Yang, Q., & Liu, W. (2018). Effects of light quality on plant growth and development. Frontiers in Plant Science, 9, 943. https://doi.org/10.3389/fpls.2018.00943

13. Sze, S. M., & Ng, K. K. (2007). Physics of Semiconductor Devices (3rd ed.). Wiley

 

Author : Dr. Emma Ziezie Mohd Tarmizi

               Senior Lecturer, Physics Unit, ASPutra

Date of Input: 16/03/2026 | Updated: 18/03/2026 | emma