Impacts of Light Colour Temperature on Plant Growth

Light colour temperature can significantly impact plant growth because different wavelengths of light have impacts upon differing physiological processes within plants. The colour temperature of light is measured in Kelvin (K) and indicates the relative warmth or coolness of light. 

Plants primarily utilise two ranges of light for photosynthesis: blue light (400-500 nm) and red light (600-700 nm). Blue light is essential for vegetative growth, leaf development, and chlorophyll production, while red light is crucial for flowering and fruiting stages. 

Plants also react and respond to UV light which whilst not being involved in photosynthesis, can trigger various physiological responses within a plant that benefit it's overall health and development. 

Here are some examples of how different grow light colour temperatures can impact plant growth: 

Cool White Light (5000-6500K): 

  • Cool white light contains higher proportions of blue light. It promotes compact, bushy growth and enhances photosynthesis during vegetative stages.
  • Ideal for growing leafy greens, herbs, and seedlings. 
  • Globes of this colour temperature are typically seen in High Pressure Sodium (HPS) and Ceramic Metal Halide (CMH) lighting systems.

Warm White Light (2700-3500K): 

  • Warm white light has more red light, which stimulates flowering and fruiting.
  • Suitable for flowering plants, fruits, and vegetables during their reproductive phases. 
  • Globes of this colour temperature are typically seen in High Pressure Sodium (HPS) and Ceramic Metal Halide (CMH) lighting systems.

Full Spectrum Light (3500-5000K): 

  • Full spectrum light contains a balanced ratio of blue and red wavelengths, supporting both vegetative and flowering stages. 
  • Mimics natural sunlight and can be suitable for overall plant growth. 
  • Very common colour temperature configuration, especially with LED grow light models.

 UV Light (Non-visible): 

  • UV light stimulates the production of secondary metabolites such as flavonoids, phenolics, and antioxidants in plants. These compounds help plants defend against UV damage, pests, and diseases, and they also contribute to the flavour, aroma, and nutritional value of fruits and vegetables.
  • UV light exposure can intensify the coloration of certain fruits, flowers, and foliage, making them more vibrant and visually appealing. 
  • UV radiation prompts plants to develop thicker cuticles on their leaves, which helps reduce water loss and enhances drought tolerance. 
  • UV light can enhance the plant's resistance to certain pathogens by activating defence mechanisms and strengthening cell walls. 
  • UV light influences various growth and developmental processes in plants, including seed germination, stem elongation, leaf expansion, and flowering time regulation. 
  • Excessive exposure to UV radiation can be harmful to plants, causing damage to DNA, proteins, and cell membranes. Therefore, it's essential to provide plants with the appropriate level of UV light without causing stress or injury.
  • UV diodes are increasingly seen built-in to 3500K - 5000K 'full-spectrum' LED grow lights.

Horticultural lighting solutions need to consider the light requirements specific to the plant variety to be cultivated beneath them, throughout their various growth stages. Adjusting the colour temperature and intensity of LED lights, growers can optimize plant growth, increase yields, and control flowering times specific to their crop type. LED grow lights are increasingly popular because they allow growers to customize light spectra to meet the needs of their crops, are energy-efficient and can be tailored to specific wavelengths, reducing wasted energy and providing cost-effective solutions for indoor and vertical farming.