Light & Plants – how they interact
Plants are dependent upon their environment for the materials and energy they require to grow in a process called Photosynthesis. Light is the primary catalyst; working in conjunction with Carbon Dioxide (CO2), nutrients, water which in turn produce energy the plant uses to grow and flourish.
Each of these environmental building blocks are required for photosynthesis and growth. Ensuring that adequate amounts of each are available is critical to the Photosynthesis process. For example, as the intensity of light increases, a plants ability to utilize the additional light depends on the availability of the other four materials. Insufficient amounts of these additional materials can slow or stop growth.
Plants extract the energy they need from light across a spectrum which is a bit broader than the human eye can see: from 400nm to 730nm. Each wavelength of light provides the plant with a different energy type. For instance, for Photosynthesis light energy is captured by Chlorophylls A and Chlorophylls B in the red and blue portion of the color spectrums. Carotenoids, which not only contribute to photosynthesis, also protect chlorophyll from destructive effects of excess light operates in the blue and blue-green spectrum. Finally Xanthophyll, another pigment which plays a large role in a plants health utilizes light in the 400nm – 530nm range. It acts as a light and heat regulator. There are more, but these are some of the most important.
So as we can see, there are many different light wavelengths at play here, and they all have different functions as it relates to a plants growth and protection. These chemical processes allow plants to cool themselves during lighted periods and to stay warm during the cool nights as well as generate energy for growth. There are many more processes at work here as we are only touching on the most common elements.
Absorption vs Photosynthetic Rate at different light wavelengths
PAR Light Spectrum
The light that plants use for photosynthesis is known as Photosynthetically Active Radiation or PAR.We see light the best in the yellow-green wavelengths, around 550nm, but PAR ranges from 400nm – 700nm, and plants primarily utilize the red and blue spectrums. PAR is also called Quantum Light. By measuring quantum light we can ensure that our plants are getting all the usable light they need (ask us about measuring light).
When looking for the appropriate lights for your garden, you will come across a multitude of terms and equations which seek to accurately describe the output of different lamps. Being able to understand the relationship between wattage and its output in lumens allows us to compare different types of lights (see our power calculators section for more information).As you may have noticed when purchasing an ordinary light bulbs, they are sold in various wattages (300w, 600W, 1000 watt, etc…). However what you may not realize is that different bulb types produce light differently. So a 20W fluorescent bulb may in fact product as much light as a 75W incandescent light. So when setting up our garden, we must ensure we accurately ascertain our plants light requirements in order to provide them with the light they need for optimal growth.Watts are a measure of how much energy a given bulb draws, whereas Output really depends on which type of bulb technology you are using. Lets look at a few of the most common types of grow lights. Then you can decide for yourself which type is best for you. We believe you will choose LED.
Types of grow lights (Pro/Cons)
All lights are trying to replicate a particular part of the suns light spectrum. Some do it better than others. Lets first start by looking at the perfect grow light – the sun!
You can see in the graph below that the sun is providing close to 100% of the complete spectrum. This is easy for the sun, however not so easy for light manufacturers as we will see below.
How the work: Fluorescent lamps work by ionizing mercury vapor in a glass tube. This causes electrons in the gas to emit photons at UV frequencies. The UV light is converted into standard visible light using a phosphor coating on the inside of the tube
Below is a representation of the typical “cool white” fluorescent lamp. You will notice the large gaps in the spectrum, as well as peaks in the green – yellow range which plants do not need much of. The reason is because plants are green, thus they don’t absorb much in that spectrum.
Typically a fluorescent lamp will last between 10 to 20 times as long as an equivalent incandescent lamp when operated several hours at a time. Under standard test conditions general lighting lamps have 9,000 hours or longer service life.
Fluorescent lamps are very efficient and convert more of the input power to visible light than incandescent lamps by 4x, however LEDs are even more efficient.
Health & Safety Issues: These lamps contain Mercury and are an environmental hazard. They cannot be thrown away, but must be disposed of at a hazardous material waste site. They also emit a small amount of UV radiation. At higher temperatures they become less efficient, thus heat can become an issue.
Natural Sunshine Fluorescent
Metal Halide Lamps (MH)
How they work:
Metal halide (MH) lamps consist of an arc tube (also called a discharge tube or “burner”) within an outer envelope, or bulb. The arc tube may be made of either quartz or ceramic and contains a starting gas (usually argon), mercury, and MH salts