What is Photosynthesis?
Photosynthesis is the process by which plants convert light into chemical energy for growth. Light provides the power source (like a battery) for plants to convert water/nutrients and CO2 into carbohydrate molecules (such as sugar), which are then stored by the plant to be used for growth.
Specialized pigments called Chlorophyll and Carotenoids are responsible for harvesting light energy used for photosynthesis. About 90% of light harvested is by Chlorophyll pigments, with 10% left to Carotenoids.
Chlorophyll comes in two primary forms, A and B. These pigments are able to absorb many colors of light; however specific wavelengths (measured in nanometers) are more efficiently absorbed than others.
Light Conversion Efficiency
The specific wavelengths of light that have the highest rate of absorption are referred to as absorption “peaks”. The graph to the left demonstrates that while Chlorophyll and Carotenoids absorb a wide spectrum of light, the wavelengths they convert most efficiently into energy are found at 439nm and 667nm for Chlorophyll A, 469nm and 642nm for Chlorophyll B, and 450nm and 525nm for Carotenoids.
Common sense dictates that when creating a grow light, the output wavelengths be as close to the absorption peaks as possible for the highest conversion rate of light energy into growth energy. It is for this reason that Hydro Grow lights use LEDs with peak output at 440nm, 470nm, 525nm, 640nm and 660nm, which match the photosynthetic peaks. This guarantees you get the fastest growth rates with the least amount of power consumed.
PAR vs Lumens
Back in 2009 Hydro Grow introduced the term “PAR” to the grow light industry, which stands for Photosynthetic Active Radiation. Prior to 2009 all grow lights were measured in lumen output, which tells you how bright a source is to the human eye. But plants and humans “see” light differently.
PAR is the region between 400nm and 700nm that is able to be absorbed by the light harvesting pigments discussed above. These pigments “see” blue and red light with the greatest sensitivity, whereas human eyes are most sensitive to green.
PAR is expressed in PPFD (photosynthetic photon flux density), which is measured in micromoles (µmol) per meter squared per second. As a point of reference, the sun delivers approximately 2000 µmol of energy at sea level on a bright sunny day, and yet there is not a single plant species on earth that can absorb this full quantity of light.
Light Saturation Point
If we think of a photon of light like a grain of salt, and photosynthesis like a glass full of water, it’s easy to understand the concept of a light saturation point. Much how water can only dissolve a certain amount of salt before it begins collecting on the bottom, photosynthetic pigments can only absorb so much light before they are maxed out.
After maxing out, supplying additional light does not equal more growth/yield. In fact supplying a plant with too much light can stunt it’s development all together (and in some plants like orchids or mushrooms, kill them). It therefore makes no sense to supply a plant with 2000 µmol if they max out at 1500, as the additional energy supplied is entirely wasted and can lead to unwanted issues. For this reason you should be wary of any light advertising more than 2000 µmol peak output, as the supplier does not understand the basic concepts described here.
Light saturation points differ from one species of plant to another, with tomatoes, watermelon, and cannabis at the highest end of the spectrum and wheatgrass, mushrooms and orchids at the lowest end. It is therefore very important that when using a grow light, you operate it within the specified range of the plant(s) you will be growing.
PAR is NOT Created Equal
While PAR is a great tool for determining how much light is available for photosynthesis, it still does not give you the ability to compare one light to another in terms of its growing potential. For example in 2010 the University of Washington ran a study with basil, spinach and lettuce under 400µmol of Hydro Grow LEDs next to 400µmol of High Output T5 Fluorescent lights. Despite plants receiving the exact same µmol intensity, plants under our LEDs grew almost twice as fast with a higher yield!
Spectrum therefore plays a vital role in plant growth as discussed in Light Conversion Efficiency above. The Hydro Grow fixture for the test utilized LEDs centered around the peak absorption wavelengths of Chlorophyll A & B, while the Fluorescent fixtures emitted a full spectrum white light. So while both lights delivered the same µmol intensity, the Hydro Grow fixture delivered this intensity via wavelengths that were more efficiently absorbed by Chlorophyll A & B, resulting in a higher conversion of the light energy towards growth and yield.
A grow light that is not properly calibrated, or that uses wavelengths beyond the base 6 used in the Hydro Grow fixture (440nm, 470nm, 525nm, 640nm, 660nm, 740nm) is wasting a significant amount of its energy on inefficiently absorbed wavelengths, resulting in lowered yields and slower growth rates. So don’t buy into the gimmick of 11, 13 and 15 “band” LED grow lights, unless you want results like the T5 fluorescent above. There is a reason Hydro Grow lights have never lost a single side-by-side grow comparison in a decade, and why our lights consistently deliver 2-4x the yield per watt of these competing LEDs. We literally wrote the “book” on the science behind LED grow lights.
The Emerson Enhancement Effect
If you’ve been paying attention you’re probably asking yourself right now “wait, where did 740nm come from? I didn’t see it discussed anywhere else on this page”. And you are correct.
Seven Colors Lighting was the first company in the world to use 740nm in grow lights; however it is not within the PAR range, nor does it correspond to any photosynthetic peaks.
Back in 1957 a scientist by the name of Robert Emerson discovered that when far red light (700-750nm) was shown simultaneously with deep red light (660-680nm), the rate of photosynthesis increased approximately 30% more than either wavelength could do on their own. In short the 740nm wavelength enhances the absorptive efficiency of red light, resulting in up to 30% faster growth rates and higher yields.
To this day Hydro Grow uses more 740nm in our grow lights than any other manufacturer. This ensures you get the fastest growth rates and highest yields known to man.
A lesser known science when it comes to plant development is called quantum effect, which analyzes how much oxygen is produced by a leaf under different colors and intensities of light. As oxygen is a byproduct of photosynthesis, measuring how much oxygen is produced indicates how fast a plant is undergoing photosynthesis.
While red and blue light are absorbed most efficiently by Chlorophyll A and B, their ability to penetrate deep into the lower chloroplasts of plant tissues is greatly lessened compared to green (525nm) or far-red (740nm) light. Despite 525nm green not being a peak absorptive wavelength of Chlorophyll A or B, when measured on the quantum scale it generates more oxygen compared to red or blue light.
Research studies show that when red and blue light are shown in the presence of green light, the green light acts as a penetrant, allowing the red and blue wavelengths to travel deeper into plant tissues resulting in greater absorptive efficiency. It’s for this reason Hydro Grow was the first company in the world to use 525nm green in LED grow lights, and uses more than any other manufacturer.
Spectrum, Time & Yield
Knowing what colors have the highest absorptive efficiency, convert the highest amount of CO2 into oxygen, or deliver a 30% boost in photosynthetic efficiency is only one part of the massive equation in creating the world’s best performing, undefeated grow lights. If the spectrum is not calibrated properly, it can have a huge impact on both the amount of time it takes until harvest and the end yield of your crop.
To maximize profitability, Hydro Grow uses a combination of 10% blue, 15% green and 75% red light (calculated on the PAR output of each wavelength). The table to the right comes from a Russian study on plant productivity, demonstrating how spectral ratios play into growth rate and yield of Starfire Tomatoes.
The tomatoes grown with our 10% blue, 15% gren, 75% red ratios had the highest yield in the least amount of time of any test group. In fact the yield was double compared to the test group at 20% blue, 60% green and 20% red, with 20 days shaved off the grow cycle!
Because of how precise the science of growing plants is, it is important to buy a grow light from a company like Hydro Grow with the knowledge and equipment to calibrate it properly for the highest yields in the shortest time. Don’t be fooled by gimmicky grow lights offering you a different spectrum for veg vs bloom, or the ability to “tune” the colors yourself with adjustment knobs. These kinds of lights were designed by amateurs and will only lessen your yields while lengthening your grow cycles compared to Hydro Grow. We didn’t just write the book on LED grow light science, we invented the test equipment that no one else on earth has to calibrate our lights perfectly for your success!