Not All Grow Lights are Created Equal

How Plants Utilize Light

Light can be divided into different wavelengths, measured in nanometers (nm). The visible  spectrum extends from 380 – 700 nm, with specific ranges appearing as different colors. Plants utilize chlorophyll pigments to absorb light between 400–700 nm range, which is typically defined as the photosynthetically active radiation (PAR) range.  Within this, light is primarily absorbed in the blue (400-500 nm) and red (600–700 nm) portions of the spectrum (Stamford et al., 2023; Wu et al., 2024). Beyond the visible spectrum, certain wavelengths of ultraviolet light have been found to stimulate plant defenses and aid in antioxidant and flavonoid production (Stamford et al., 2023). Additionally, far-red light (700-900 nm) up to 750 nm can be utilized in photosynthesis and is sometimes included in the definition of PAR (Stamford et al., 2023; Zhen et al., 2022).

Since pigments and photoreceptors regulating distinct cellular processes absorb light in different parts of the spectrum, the ratio of blue to red light can influence plant growth patterns (Wu et al., 2024; Dunn & Mill, 2017). This includes stem elongation, leaf development, and flowering. Blue light is generally associated with compact, vegetative growth, whereas red light typically promotes stem elongation and flowering. However, this varies among plant species (Dunn & Mill, 2017; Runkle, 2017). Although standard house lights emit light in the blue and red range, their output is typically too weak for effective plant growth.  

Factors Influencing Grow Light Performance

Three main types of grow lights are available, including fluorescent lights, high-intensity discharge (HID) lights, and light-emitting diodes (LED). Light quality, light intensity, energy efficiency, and heat emission vary significantly among them. 

• Light intensity is quantified by the amount of photons hitting a given area in a certain amount of time (photons per square meter per second). This is important because it directly affects the quantity of energy for photosynthesis (Wu et al., 2024). Lights with low intensity tend to need to be positioned extremely close to plants and can result in elongated stems, thin leaves, and yellowing. 
• Light quality, otherwise known as spectral composition, refers to the mix of wavelengths emitted by a grow light. While certain grow lights exclusively emit predominantly red or blue light, others offer control over the portion of the spectrum emitted.

Although these factors vary among the different types of grow lights, they also differ between specific light models within each category. Regardless of which type of grow light you choose, these features should be considered before purchasing.

Fluorescent Lights

Fluorescent lights are affordable and easy to use, making them desirable for many beginners. They predominantly produce light in the blue spectrum, making them suitable for vegetative growth of some seedlings and young plants (Steil, 2023). Fluorescent grow lights may also be effective for low-light leafy greens, such as lettuce or herbs. Fluorescent light intensity is less than LEDs and HID, meaning they typically yield poor results for light-demanding plants.  

Although their cost is low, they are far less energy efficient compared to LEDs and HIDs (Dunn & Mill, 2017). Consequentially, they also emit heat. While many assume additional heat may be beneficial for growth, it can damage plants when positioned too close and becomes particularly problematic when multiple lights are clustered together. 

HID (High-Intensity Discharge)

HID grow lights are extremely powerful. Although less common in small indoor setups, they are commonly used in many commercial operations. While they consume more energy than LEDs, their light output is exceptionally high. Different kinds of HID lights, including high pressure sodium and metal halide, can be utilized for specific growth stages, allowing for greater optimization of plant growth (Steil, 2023; Rothenberger, 2016).  

• HPS (High-Pressure Sodium) HIDs predominantly emit red and orange wavelengths of light, with limited amounts of blue and green.  
• MH (Metal Halide) HIDs primarily produce blue, green, and orange light.  

The greatest downsides to HIDs are their high energy usage and heat output. This tradeoff is worth it to many commercial growers due to the impressive yields HIDs can provide in systems needing large quantities of artificial light, making it worthwhile to invest in cooling systems. Their lifespan is approximately 24,000 hours, which is lower than LED but significantly higher than fluorescence (Dunn & Mill, 2017). 

LED (Light-Emitting Diodes) 

The use of LED grow lights has increased rapidly in the horticulture industry and among home growers (Shelford & Both, 2021). By using different colored diodes in one fixture, growers are able to change the ratio of red and blue light being emitted (Fylladitakis, 2023).  

LEDs are capable of converting a large portion of electricity to usable light, making them extremely efficient. This, combined with their extended lifespan (up to 50,000 hours) makes them the most environmentally friendly option (Dunn & Mill, 2017). They produce little heat, allowing them to be placed close to seedlings without fear of heat damage. Purchasing LED lights is typically the most expensive, but the low cost of running them has caused many to shift in preference to them (Stamford et al., 2023). 

Sources & Additional Information

Dunn, B. & Mill, T. (2017). LED Grow Lights for Plant Production. Oklahoma State Extension. https://extension.okstate.edu/fact-sheets/led-grow-lights-for-plant-production.html?utm

Fylladitakis, Emmanouil. (2023). Controlled LED Lighting for Horticulture: A Review. Open Journal of Applied Sciences. 13. 10.4236/ojapps.2023.132014.

Rothenberger, R. (2016). Lighting Indoor Houseplants. University of Missouri Extension. https://extension.missouri.edu/publications/g6515?utm

Runkle, E. (2017). Effects of Blue Light on Plants. Michigan State University Extension. https://www.canr.msu.edu/floriculture/uploads/files/blue-light.pdf

Shelford, T. J., & Both, A.-J. (2021). On the Technical Performance Characteristics of Horticultural Lamps. AgriEngineering, 3(4), 716-727. https://doi.org/10.3390/agriengineering3040046

Stamford, J. D., Stevens, J., Mullineaux, P. M., & Lawson, T. (2023). LED Lighting: A Grower’s Guide to Light Spectra. HortScience, 58(2), 180–196. https://doi.org/10.21273/HORTSCI16823-22

Steil, A. (2023). Sources of Supplemental Light for Indoor Plants. Iowa State University Extension and Outreach. https://yardandgarden.extension.iastate.edu/how-to/growing-indoor-plants-under-supplemental-lights/sources-supplemental-light-indoor-plants?utm

Weisenhorn,  J. & Hoidal, N. (2024). Lighting for indoor plants and starting seeds. University of Minnesota Extension. https://extension.umn.edu/planting-and-growing-guides/lighting-indoor-plants?utm

Wu, W. & Chen, L. & Liang, Rentao & Huang, Shiping & Li, Xiang & Huang, Bilei & Luo, Huimin & Zhang, Miao & Wang, Xiaoxun & Zhu, Hua. (2025). The role of light in regulating plant growth, development and sugar metabolism: a review. Frontiers in Plant Science. 15. 10.3389/fpls.2024.1507628.

Zhen, Shuyang & Van Iersel, Marc. (2022). Photosynthesis in sun and shade: the surprising importance of far‐red photons. New Phytologist. 236. 10.1111/nph.18375.