Plants use light in the 400–700nm range for photosynthesis (PAR — photosynthetically active radiation). Red light (600–700nm) is particularly important for flowering and fruiting, while blue light (400–500nm) drives vegetative growth. While "red light therapy" usually refers to human/animal treatment, the same wavelengths are used in horticultural grow lights.

How Plants Use Light

Plants use light for two main processes:

  • Photosynthesis: Converting light energy into chemical energy (sugars). Uses primarily red and blue light.
  • Photomorphogenesis: Light-driven development (germination, flowering, stem growth). Uses red, far-red, blue, and UV light.

Red light (600–700nm) is the most efficient wavelength for photosynthesis. Plants grown under red light tend to be larger but may have smaller leaves. Blue light promotes compact, leafy growth.

Wavelengths for Plants

  • 660nm (deep red): Drives photosynthesis and flowering
  • 730nm (far-red): Triggers flowering in some plants; end-of-day light cycles
  • 450nm (blue): Drives vegetative growth and compact form
  • 380nm (UVA): Boosts pigment production (purple/red colors)

Most grow lights combine red and blue wavelengths in different ratios depending on the growth stage.

Red Light in Grow Lights

The red light panels sold for human therapy (660nm) are essentially the same wavelength used in horticultural grow lights. However, plant-specific grow lights are usually a better investment because:

  • They include blue light (essential for vegetative growth)
  • They have higher intensity (plants need more light than humans)
  • They're designed for plant light cycles (12–18 hours daily)
  • They're typically cheaper per watt than human RLT panels

If you already own a human RLT panel and want to experiment, you can use it on plants — but dedicated grow lights are more effective and cost-efficient.

Frequently Asked Questions

Technically yes — 660nm red light drives photosynthesis. But dedicated grow lights are more effective because they include blue light and have higher intensity. Use a real grow light for serious plant growing.
Red (660nm) for photosynthesis and flowering, blue (450nm) for vegetative growth. Most grow lights combine both.
Marginally. If your houseplants aren't getting enough natural light, a grow light is a better investment than a human RLT panel.
Same wavelengths (660nm), but grow lights are higher intensity, include blue light, and are designed for long daily use (12–18 hours). Human RLT panels are designed for short therapeutic sessions.
Not directly for photosynthesis. But far-red (730nm) light affects flowering cycles in some plants. 850nm is mostly wasted on plants.
Plants need 12–18 hours of light per day for optimal growth. Human RLT panels aren't designed for this duration — get a real grow light.

For Human Use Only

This site focuses on human RLT. For plants, get a dedicated grow light — they're cheaper and more effective.

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