Grow Lights and Plant Growth
How light spectrum impacts plant growth and development
When we talk about optimizing our grow space for plant growth and development, we’re talking about two different types of change: Plant growth refers to how much plant there actually is in dry weight. Meanwhile, plant development is all about the shape of the plants.
Photosynthesis impacts plant growth, but doesn’t have the same effect on plant shape, as the way plants process light is the same in just about every species. In the same vein, colored lighting doesn’t really have an impact on photosynthesis; your plants will still absorb and produce the energy they need. However, using different colored lighting can dramatically impact your plant’s development. Color can change the height, thickness and leaf production, meaning it’s pretty important to get the right spectral quality when trying to grow good, and effective yields.
What’s more, the way the light impacts plants differs from species to species, so there will be some level of research or trial and error required to find the perfect light combinations for your specific plant type.
In this guide, we’re going to discuss the main effects of spectral quality, and how LEDs incorporate everything you need to create the perfect environment.
The importance of grow light for plants
It’s no secret that plants need a good amount of light to grow. But until you start to dive deeper, it can be easy to think that’s the end of the line. In fact, lighting affects just about all other parameters for plant growth – meaning it’s crucial you get it right.
For example, more sunlight has always meant that more water has to travel through the plant from the roots to keep it cool. It also impacts the temperature and humidity which makes CO2 more or less efficient for use.
There are 9 main factors that must be optimized to encourage plant growth:
CO2, nutrients, oxygen, water, root temperature, temperature above ground, humidity, wind and light.
In the past, we’ve only been able to depend on what the sunshine has to offer. But now, with the help of grow lights, we can significantly change how much light our plants get, and the color of photons they receive. Then, all other parameters can be optimized in accordance.
Different photon colors and the effect on plant development
Originally, horticulturalists, biologists and physicists worked with three different photon colors: Blue, green and red. However, there is now the use of far-red as well.
When plants absorb blue light photons, their growth can become stinted. While this at first sounds bad, it can keep plants shorter and stop stem elongation – making it easier to manage them in smaller grow spaces. This is particularly useful for commercial, vertical farms as you want to keep the plants healthy and strong, but short to save space.
Blue photons are heavily absorbed by chlorophyll A and B in the plant leaves – making it difficult for blue to penetrate the plant in the same way.
In terms of the efficiency (watts of photosynthesis in, per watt of electricity out), blue LED chips are 88% efficient. White, red and far red scored 80%, 69%, 66% respectively.
Green photons absorbed by the plant allow us humans to more easily identify issues in growth and development. It’s green that helps us notice nutritional issues, pests, illness and disease.
Originally, LEDs were made with just blue and red photons as it was rumored that green photons weren’t used efficiently. This was a misconception. Newer LEDs are created with a mixture of red, green and blue to create a bright white lighting, so that your plants have access to everything they need.
To drive photosynthesis, you want to make sure there’s a lot of red photons within your light. They’re about 15% more effective than blue photons for photosynthesis.
Far red is quite a new concept, and can be used to counteract the effectiveness of blue photons. Essentially it can help to create long and tall plant stems through dramatic cell expansion.
However, the effects of far-red photons are very varied. It is particularly good for leafy greens like lettuces.
Far red has the highest level of penetration. In the 1950s, Emerson discovered the ‘enhancement effect’ of far-red photons: When paired with shorter wavelengths, far-red can actually offer photosynthetic radiation (PPFD/PAR) to up to 730nm, when previously it was suggested to reach only 700nm.
Why are LEDs more efficient for colored photons?
When comparing LED grow lights to traditional HPS lighting, there are two main reasons why LEDs are much more efficient when trying to provide your plants with all the different photons they need: Cost and umol per joules.
Cool white LEDs are the most cost effective, as the LED chips are mass produced - making the overall cost cheaper. For red, blue and far-red LED chips, the prices are much higher (10-30 times) as they are less common. Some plants aren’t actually impacted by blue photons provided by LEDs; they’ll still provide the same yield as HPS lighting, but the LEDs are slightly cheaper to run.
When it comes to umol per joules, this is where LEDs really outshine HPS lighting. HPS lighting has a rating of around 1.7 while the LED counterparts have over twice this efficiency. (Blue has 3.3, Red 3.8, Far Red 4, White 3).
It’s clear that LEDs are more efficient for those looking to keep costs down. However, HPS lighting has its perks too. You can check out our guide to the different grow lighting here.
Hopefully this guide should have given you a better idea about the need for all colours in the lighting spectrum. However, as ever, if you need any help – be sure to get in touch!