Indoor Gardening isn't exactly new, but LEDs are changing the way we light our indoor gardens. LED lights are more efficient than traditional fluorescent and incandescent lights. This is because LED lights convert almost all of their energy (95%) into light, while other lights convert a significant amount of energy into heat rather than light. However, there is another very important reason why LEDs are more efficient when it comes to growing plants. With LED lights, we have a rather unique ability to customize the type of light emitted, and that means we don't waste energy creating light that doesn't help our plants grow. By the end of this post, you will understand the reason behind why grow lights come in many different colors and also why some LED grow lights cost much more than others.
Plants Use Only the Visible Light Spectrum for Photosynthesis
It's important to know that plants only use visible light (the colors of light we see every day) for photosynthesis. However, the full spectrum of light is much larger than the spectrum of only visible light. At the outer edge of the visible light spectrum are Ultraviolet (UV) light and Infrared Radiation (IR). UV light is invisible light emitted from the sun and other sources that will cause sunburns when we don't use sunscreen. IR light can only be seen with special equipment such as night vision goggles. Even further beyond the visible light spectrum are light waves that we don't traditionally think of as light. These include X-rays, Microwaves, and even Radio Waves.
One of the most important things to understand is that scientists have proven time and again that plants absorb only visible light for photosynthesis.Plants respond to other forms of light, such as UV, but this reaction is typically negative. It was said that marijuana growers actually use UV light to stimulate the production of psychoactive chemicals like THC, which seems to be produced in part as a defense mechanism against the harmful effects of UV light on the plant.
What is PAR?
PAR stands for "photosynthetically available radiation". PAR consists only of visible light because it is the only light plants use for photosynthesis.
For decades, many indoor growers have used Lumens to measure the effectiveness of a grow light, but the industry is getting smarter and turning to PAR. Lumens are used to measure the brightness of a lamp to the human eye. But plants and humans see light differently. People see yellow and green brighter than other colors. Therefore, the Lumen values of yellow and green lamps may be higher than red and blue lights, which emit the same amount of real light and which plants will respond better.
PAR evenly measures all light from the visible light spectrum and does not measure light outside the visible light spectrum, which does not aid plant photosynthesis. So for plants, a light's PAR value is currently the best basic measure of the brightness of a growing light. Accurate PAR meters are quite expensive and usually cost $500 or more. Faulty PAR counters can be purchased much cheaper, but there's really no point in having a faulty PAR counter.
Assuming you don't want to buy your own PAR meter, the best way to get PAR values for your grow lights is to talk to us about their lights' PAR rating.
How Much PAR Do My Plants Need to Grow?
The amount of PAR your plants need depends on what you're growing and also how far the light is from your plants. Generally speaking, leafy greens like lettuce only need a PAR of ~200, while tomatoes and other plants that bloom and bear fruit require a PAR of 400-500 or more. If you don't place your grow light directly above your crop, you will need an even higher PAR rating from your grow light to account for the distance between your plant and the light source.
In the example below you can see a very strong grow light that emanates approximately 1,900 PAR (measured in umol) 20cm from the source. Few lights extinguish that much PAR, and they are often quite expensive. This light emits 1,900 umol every second. But at a distance of 58cm from the source, the power of the light is reduced to 890 umol. The further away from the light source, the lower the PAR value. When we are 2 meters away from the light source, our PAR drops to ~100umol, which means we will have trouble growing lettuce well. Therefore, you should always make sure you know that not only is the PAR emitted from the light, but for every 20cm away from your light the PAR will decrease by ½ or more.
There are many inexpensive grow lights on the market that make big claims, but they will eventually disappoint their owners. This problem is very common especially on the internet. Don't forget to check the PAR value of any light you buy. Also, don't forget to take into account how far your light will be from your plant to ensure there is enough photosynthetically available radiation (PAR) for your plant to thrive.
Leafy Greens require 200 PAR for proper growth
Tomatoes, cucumbers and other flowering/fruiting vegetables require 400-500 PAR
Fruit Trees should be given 600 PAR and above.
What Light Temperature Should I Use?
Interestingly, 'Kelvin temperature' is the measure used to describe the visual color emitted by a light. As you can see in the chart below, "warmer" light temperatures that have a red color have a lower Kelvin rating. At the other end of the spectrum are "cold" temperature lamps that are blue in color and have a higher Kelvin rating.
Different light temperatures have different effects on plants. In general, light at higher temperatures (blue) promotes photosynthesis, leading to bushy plants that are not prone to elongation and access to more light. This is great if you want to grow in a compact space. Low temperature (red) light reduces photosynthesis and signals to plants that it is time to flower and bear fruit. Plants kept under red light will tend to stretch more and grow taller as opposed to growing denser and more compact.
Soli Lighting focuses on providing full spectrum lights with a natural color temperature between 4500K-6500K as they are the most pleasing to the eye. They also allow plants to grow bushy and compact, without hindering the plants' ability to bloom and bear fruit.
What Color Light Should I Use?
LED lights can come in almost any color. Plants respond best to red and blue light. Interestingly, plants generally respond less to green light. In fact, the reason plants appear green is because they tend to reflect green light while absorbing other parts of the light spectrum more easily. For this reason, large-scale or industrial plant growers often use a combination of red and blue lights to photosynthesize their plants. They don't want to waste electricity by producing green or even yellow light that plants use less efficiently.
But for those of us who grow crops in our living spaces, it's worth the extra penny we spend to produce a beautiful full spectrum color that is more natural and pleasing to the eye. Full spectrum grow lights usually come with a chart showing the distribution of emitted blue, green, yellow and red light.
As a result
We hope this article has given you a comprehensive background on indoor grow lights and what to consider when you decide to purchase them. Remember to make sure your grow light has the appropriate PAR rating for the particular plant you are growing. Additionally, if you're growing your plants in a recreational part of the house, make sure you get a light in a color you enjoy, usually between 4500 and 6500 Kelvin.
Feel free to reach out to us for more helpful tips on indoor gardening and suitable LED lights.