How to improve controlled environment crop production with LED lighting

By Karla Garcia, Technical Service

The development of new lighting technologies such as light-emitting diodes (LEDs) can increase the capability to provide ideal light conditions to crops. This makes it possible to improve crop performance and product quality.

Response to light quality

Each crop has a particular response to light quality. By providing a particular light spectrum to plants, plant growth, development and photomorphogenesis reactions can be controlled. Photomorphogenesis is a process by which plants produce phytochemicals in response to light signals. Phytochemicals present in vegetables have an impact on people’s health. The biosynthesis, metabolism and accumulation of phytochemicals can depend on light quality. This means providing a specific light spectrum to plants can control plant shape, growth and also have an impact on taste, aroma, chemical compounds, nutrition quality, etc.

Optimum light spectrum

How do you know which light spectrum is optimum for your crops? Several studies on light quality have been done for common crops. There is still much research needed to fully understand how each crop responds to light quality. However, enough information is available to develop lighting technologies to help improve crop production. The following information provides a summary of recent research on light quality for common crops.

TOMATO

Light quality	Plant response
Far-Red LIGHT	By lowering R:FR ratio, tomato seedling stem elongation was significantly increased (Chia and Kubota, 2010).
Red light	Use of supplemental red light increased tomato fruit yield by 14 percent (Lu et al., 2012) and chlorophyll content compared to the control treatments (Yang et al., 2018).
Green light	Partial replacement of blue and red light with green light increased growth of plants in dense canopies improving yield, chlorophyll and carotenoid concentration (Kaiser et al., 2019).
Blue light	Proved to be required for normal chloroplast structure (Lu et al., 2012) and reduced internode length (Menard et al., 2006; Nanya et al., 2012). Used alone blue light tends to reduce yield and photosynthesis efficiency compared to red light (Lu et al., 2012; Menard et al., 2006).
ULTRAVIOLET light	There was a significant increase in carotene concentration when plants were exposed to UV light before harvest.

LEAFY GREENS

Light quality	Plant response
Far-Red light	Increased total biomass and leaf elongation (Stutte et al., 2009), decreased anthocyanin concentration (Stutte et al., 2009; Li and Kubota, 2009).
Red light	Pre-harvest exposure reduced nitrate concentration (Wanlai et al., 2013; Ohasi-Kaneko et al., 2007; Samouliene et al., 2009; Samouliene et al., 2011). Increased phenolic (Li and Kubota, 2009; Zakauskas et al., 2011) and carotenoid (Brazaityte et al., 2014) concentration.
Green light	High light intensity promotes growth compared to fluorescent lamps (Johkan et al., 2012), reduced nitrate concentration and increased ascorbic, tocopherol and anthocyanin content (Samuoliene et al., 2012).
Blue light	Increased ascorbic acid (Ohashi-Kaneko et al., 2007), B-carotene (Lefsrud et al., 2008), anthocyanin (Ohashi-Kaneko et al., 2007) content, leaf expansion (Stutte et al., 2009) and root growth (Johkan et al., 2010). Decrease nitrate concentration (Ohashi-Kaneko et al., 2007).
UltraViolet light	Increased anthocyanin concentration (Li and Kubota, 2009).

CUCUMBER

Light quality	Plant response
Far-Red light	Stimulated stem elongation and leaf expansion at lower R:FR (Shibuya et al., 2019). Increased stem dry weight and sugar content (Cu et al., 2009).
Red light	Increased number of leaves, root and shoot growth (Marques da Silva et al., 2016).
Green light	Increased growth, leaf area fresh and dry weight (Brazaityte et al., 2009; Samuoliene et al., 2011; Novickovas et al., 2012) compared to high pressure sodium (HPS) lamps.
Blue light	Increased leaf area, fresh and dry weight and photosynthetic pigments compared to natural light and HPS lamps (Samuoliene et al., 2012). Decreased hypocotyl elongation (Novickovas et al., 2012; Hernandez and Kubota, 2016).
UltraViolet light	Positive results controlling powdery mildew (Suthaparan et al., 2017).

PEPPER

Light quality	Plant response
Far-Red light	Increased plant height and stem mass compared to red light alone (Brown et al., 1995).
Red light	Increased number of leaves per plant and shoot length (Marques da Silva et al; 2016; Tang et al., 2019).
Green light	Increased leaf area (Samouliene et al., 2012), growth, yield phenolic and carotenoid content compared to HPS lamps (Guo et al., 2016).
Blue light	Suppressed plant growth and biomass formation compared to cool white fluorescent lamps when used in high amounts (Hoffmann et al., 2015).

CANNABIS

Light quality	Plant response
Red light	Significantly increased yield, tetrahydrocannabinol (THC) (Hawley et al., 2018) and cannabidiol (CBD) (Magagnini et al., 2018) content in bud tissue.
Green light	Significantly increased α-pinene, borneol (Hawley et al., 2018) and THC in bud tissue and antioxidant capacity compared to sunlight (Livadariu et al., 2018).
Blue light	Increased polyphenols, flavonoids, fresh weight and protein compared to sunlight (Livadariu et al., 2018).