Light spectrum for plants: effect on growth and flowering
What does light do to plant development? If you have ever grown plants, you have probably noticed how much influence light has on their growth and flowering. The light spectrum of your grow light plays a crucial role in this.
In this article, we explain how different light colors (wavelengths) affect plant development and how you can apply this when choosing the right grow lighting.
🌿 Photosynthesis and more
Everyone knows that plants need light for photosynthesis. During this process, the plant converts light into energy (sugars) needed for growth.
Want to know more about this? Read our article on photosynthesis in plants.
But light does more than just provide energy. It also influences:
- Photomorphogenesis – how a plant grows and develops
- Photoperiodism – when a plant starts to flower
👉 So light is not only fuel, but also an important signal for the plant.
🌈 What is the light spectrum?
Light consists of electromagnetic radiation and can be described by wavelength. For plants, the range between 400 and 700 nanometers (nm) is particularly important.
This is called PAR (Photosynthetically Active Radiation). Within this range are all the light colors that plants use for growth and flowering.
📊 PAR and PPFD explained
In addition to PAR, PPFD (Photosynthetic Photon Flux Density) is often discussed.
- PPFD is measured in µmol/m²/s
- Indicates how much usable light a plant receives
👉 Most plants need at least 30 – 50 µmol/m²/s to survive.
🌱 How does a plant react to light?
Plants use light not only for energy, but also as a source of information. Through special pigments (photoreceptors), they "read" their environment.
There are three important groups:
- Phototropins – direct growth towards light
- Cryptochromes – regulate growth and development
- Phytochromes – respond to red and far-red light
👉 These together determine how a plant grows and flowers.
🔵 Effect of blue light (400 – 500 nm)
Blue light is essential for the growth phase.
- Compact growth
- Shorter stems
- Thicker leaves
👉 Too little blue light results in long, weak plants and less sturdy growth.
Most plants need 5 – 30 µmol/m²/s of blue light.
🔴 Red and far-red light
Red and far-red light play an important role in the flowering and stretching of plants.
- Red light stimulates flowering
- Far-red light influences plant length and timing
The ratio between red and far-red light is crucial for plant development. Read more about the optimal red/far-red light ratio (R/FR).
🌸 Effect on the flowering phase
Flowering is strongly influenced by phytochromes.
- More far-red light can lead to faster flowering
- The timing of light and dark is essential here
👉 This plays an important role, especially in short-day plants.
🟢 Green light (500 – 600 nm)
Green light was long underestimated, but it certainly plays a role in plant development.
Research shows that adding green light can lead to more biomass and better growth, especially in combination with red and blue light.
☀️ Ultraviolet light (300 – 400 nm)
UV light affects the structure of plants:
- More compact growth
- Smaller, thicker leaves
👉 Note: too much UV light can be harmful to plants.
✅ Conclusion: what does this mean for your grow?
For optimal plant growth, a balanced light spectrum is essential:
- Minimum 30 – 50 µmol/m²/s of light needed
- Sufficient blue light (5 – 30 µmol/m²/s)
- Enough red and far-red light for flowering
- A good balance between red and far-red light
👉 Modern LED grow lights optimally combine these spectrums.
🛒 Which grow light suits your situation?
Do you want to know which lighting is best for your plants?
👉 Then also read our article: Which grow light to choose?