I've gone through my fair share of different grow lights. Some cheap, some expensive, but each season of growing I've learned something new and continue to improve my setup. One major factor in my success has plant been choosing the right lighting. Plants need light!
Plants are remarkable organisms capable of harnessing light energy from the sun and converting it into the fuel they need for growth through a process called photosynthesis. However, certain wavelengths are better utilized than others.
Let's take a quick high level review on how plants make food. And hopefully you'll walk away with some ideas to improve your planting success by the type of light you are providing them.
Photosynthesis: A Brief Overview
Photosynthesis is the biological process that enables plants to convert light energy into chemical energy, specifically in the form of glucose. This intricate process takes place in the chloroplasts, specialized organelles found in plant cells. The primary players in photosynthesis are pigments, including chlorophyll A, chlorophyll B, and carotenoids.
Chlorophyll A and Chlorophyll B:
Chlorophyll A and chlorophyll B are the two main types of pigments responsible for capturing light energy during photosynthesis. These pigments absorb light in different regions of the electromagnetic spectrum. Chlorophyll A absorbs light most effectively in the red and blue-violet parts of the spectrum, while chlorophyll B complements this absorption by capturing light in the blue and red-orange regions. These spectrums are between the 400-700nm wavelengths
Carotenoids:
Carotenoids are accessory pigments that broaden the range of light absorption in plants. These pigments absorb light in the blue and green regions of the spectrum, complementing the absorption spectra of chlorophyll A and chlorophyll B. Carotenoids also play a crucial role in photoprotection by dissipating excess light energy as heat, preventing damage to the plant's photosynthetic machinery.
Effects of Light Colors on Plant Growth:
The color of light plays a significant role in the growth and development of plants. Different wavelengths of light have varying effects on photosynthesis and plant morphology. Here's a brief overview of the effects of different light colors:
**Red Light (620-750nm)
- Triggers the germination process
- Promotes flowering and fruiting
- Enhances photosynthesis and overall plant growth
**Blue Light (450-500nm)
- Stimulates chlorophyll production, promoting leaf and stem development
- Essential for seedling root development
- Influences phototropism (ability of the plant to re-orient the shoot growth towards a direction of light source)
- Helps regulate plant stomata (pores on leaf surface)- used to uptake CO2 and release O2
**Green Light (495-570nm)
- Least effective in driving photosynthesis compared to blue or red
- Penetrates deep into the plant canopy, influencing lower leaves
- Promotes plant defense mechanisms
** UV Light (10-400nm)
- In moderate doses, can promote plant defense mechanisms to UV radiation
- High levels can damage plant tissue and inhibit photosynthesis
**Far-Red Light(700-1000nm)
- Influences the plant's photoperiod response, affecting flowering.
-High levels can cause wilting or burning
- Can influence plant metabolic rate for improve plant growth
LED Grow Light Spectrum:
The low power and cost of LEDs has led to the development of LED lights with specific spectrums to promote plant growth. By understanding their specifications, growers can optimize their plant growth and development.
Spectrum Charts
Spectrum charts are used to show a lights wavelength and intensity of light. This can be used to determine if the light has the correct specifications for growing plants and to compare to other manufacturers.
It is important to pay attention to the valleys at peaks on the chart to match the spectral needs of the plants being grown. Often a spectrum ratio of red light to blue light is displayed as a single number.
Full Spectrum Lights
Designed to provide a natural full spectrum of light that mimics sunlight. They usually include a mix of warm and cool LEDs, as well as important specific wavelengths.
Broad Spectrum Lights
These lights are a similar to full spectrum but have a more even distribution of visible light wavelengths. This makes them a good balanced light source that isn't too focused on specific growth stages.
In most cases, a growers needs can be met by using a broad spectrum or full spectrum light. If a grower has specific needs they can also opt for a target spectrum light. These are less prevalent in the market and will be a higher cost that the more readily available broad and full spectrum grow lights.
Color Temperature(k) and Spectrum
Color temperature is a measure of a lights visible appearance measure in Kelvin(K). A lower temperature (K) will produce a warmer red-yellow light, compared to higher temperature (K) which produces a cool blue-white light.
What do the Manufacturers Specs Mean?
- PAR- Photosynthetically Active Radiation
- Defines the wavelength spectrum of light. This is range displayed on your light spectrum chart
- PPF- Photosynthetic Photon Flux
- Measure of the total amount of light in the PAR zone produced each second. Expressed in umol/s units
- PPFD- Photosynthetic Photon Flux Density
- The takes into account the amount of PPF that falls on the specified area. Expressed in umol/m2/s
- DLI- Daily Light Integral
- Cumulative measure of amount of light that reaches your plants in a day
- Expressed as mol/m2/d
- DLI=PPFD x light hours per day x (3600/1000,000)
As a general rule of thumb. Use the chart below when determining your lighting needs at each plant stage.
| Plant Stages | DLI (mol/m2/d) |
| Seedling/ Microgreen | 6-12 |
| Vegetative Growth | 12-17 |
| Flower/ Fruiting | 15-40 |
If you need to know the outdoor DLI for your area you can use this link to an interactive map. You can sort by seasonal month or annual DLI data.
Which Spectrum for Each Plant Stage
Seedling
Look for a full spectrum light in the 5000-6500k color temperature range.
Vegetative
Look for a balanced light with slightly higher ratio of blue light. Color temperature in the 4000-5000k range.
Fruiting & Flowering
During this stage, plants require a higher ratio of red light. Which stimulates flowering hormones as part of their reproductive stage. Recommended color temperature is 3000-4000k.
Light it up!!
Phew, we definitely covered a lot of information in this one! Hopefully there's at least a bit of information you can glean and implement in your setup looking to make some improvements.
Also I'm not going to pretend like I have all the answers. Below are links to great resources that were culminated both for my personal use and for the topics of this post. If you want to learn more check out the links below.
Links:
Oklahoma State University Study