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Moving production into an insulated building is suitable for producers who want to be close to urban markets, have a lack of arable land, or live in a climate not suitable for outdoor or greenhouse production.
No matter where a plant is grown, it still requires optimal conditions to reach its maximum yield potential. In addition to the controls discussed above, producers must also provide light suitable for optimal plant growth. For plants, light stimulates seed germination, food production, flowering, chlorophyll manufacturing, and branch and leaf thickening.
Photosynthesis is stimulated by the type and frequency of light received. Light is emitted as waves of photons, or bundles of energy. The amount of energy in each photon determines the length of the wave from crest to crest. Lower energy wavelengths emit a blue light (400 nm) and higher energy wavelengths emit a red light (700 nm). Plants utilize wavelengths between 400-700 nm. Blue and red light is required in different ratios at different periods in the plant\'s life. Blue light is primarily responsible for vegetative growth. Red light triggers cell elongation, vegetative growth, and flowering.
Traditional plant grow lights are fluorescent (FL) or high intensity discharge (HID) fixtures. Compact T5, T8, and T12 FL bulbs are mainly used for seed propagation or vegetative growth. HID fixtures are often sold to accommodate both metal halide (MH) and high-pressure sodium (HPS) bulbs. Light produced by MH bulbs is the 400-550 range, suitable for vegetative growth. Light produced by HPS bulbs provide light in the yellow, orange, and red spectrum, more suited for flowering and fruiting stages. Both FL and HPS bulb have a lifespan of 20,000+ hours and generate a considerable amount of heat.
Advances in plant grow lights have made indoor production more cost effective through improved energy efficiency and higher plant yields. Induction fixtures (IND) are similar to FL bulbs but have become more popular, as they have no electrodes allowing them to last considerably longer (75,000+ hours). They also put off much less heat and are more energy efficient. Light emitting diodes (LED) lights were once too expensive for many growers; however, they are now considered the standard for plant grow lights. LED lights operate by passing an electrical current through two semi-conductors (one positive, one negative) which then emit light. The spectrum can be dialed into what is required by the plant at different stages, improving the quality and yield of the crop. In addition to improved energy efficiency, LED lights have a lifespan of 100,000+ hours.
Research conducted at Kentucky State University compared growth of six leafy greens and energy use for FL, MH, IND, and LED grow lights. LED lights produced significantly higher plant biomass (g/m2) compared to the other three lights (Figure 28: KSU unpublished, Oliver et al. 2018). As the cost of LED lights continue to decrease, production costs for indoor plant production will also decrease.
Source: Janelle Hager, Leigh Ann Bright, Josh Dusci, James Tidwell. 2021. Kentucky State University. Aquaponics Production Manual: A Practical Handbook for Growers.