In this article, we will share with you some differences of growing with LEDs as well as some practical tips to maximize your yields. First, though, we’ll look at a fundamental difference between HID and LED light. This difference is the key to understanding what makes growing under LED different.
Why Growing under LED is Different from HID: Infrared Radiation
One of the biggest differences between HID and LED is the amount of infrared they produce. For HPS, as much as 60% of the light they emit is infrared. For ChilLEDs, it’s just a few percent and only in the far red range.
HID lights, such as HPS and metal halide, operate at temperatures of 3,0000C or 5,4000F. That’s hot enough to vaporize the metals inside the bulb so that an arc of electricity can be maintained. At common HPS light levels, infrared radiation can heat up a plant’s leaves by 5 to 100F.
The result of this heat is that plants transpire more under HPS. Transpiration is the evaporation of water, primarily from a plant’s leaves, to cool itself and pull more water and minerals up from the roots. Below we’ll look at some of the practical implications of this difference and others.
1) With LEDs, you can safely provide more light to your plants.
Since LED light doesn’t contain as much infrared radiation, you can safely provide more of it to your plants without risk of damaging them. This is a dream come true for CO2 growers that want to maximize their results for a given grow space.
2) With LEDs, you’ll save a lot on your cooling bill because you can and should keep your ambient temperature higher.
Grow rooms that use HPS have to stay cooler because of how much the HPS infrared radiation heats up the plants. If they let the room heat up too much their plants will become damaged and inefficient. For instance, if a grow room is 85oF/29oC and a HPS heats up your plant’s leaves by another 7 degrees or more, then your plants have now reached into the 90’s F / upper 30’s C. The effects of this can dramatically affect your bottom line of harvest.
With LEDs, you can and should keep your plants at between 83 and 85oF. This saves you on your cooling bill and optimizes your plant’s growth. At this range of temperatures, the chemical reactions involved in photosynthesis take place faster and more effectively.
As you begin to keep your ambient temperature higher and you primarily accomplish that through reduced ventilation, you will want to pay attention to three related environmental parameters – humidity, CO2 concentration, and the difference between your daytime and nighttime temperatures.
Higher ambient temperatures have the ability to both hold more water and evaporate more water. This can be fine within a certain range, but if the humidity gets too high then plant fungal infections can become an issue. To combat that, it may be wise to dehumidify and/or ventilate more.
This topic can become acutely important when you have an excessive range of temperatures between your day and night times. If during the day you have very warm conditions with high relative humidity followed by a very cool night, then the likelihood of dew forming on your plant becomes high. This can quickly become fungal heaven.
There are many ways to tackle this complex subject and keep your plants within optimal ranges, but one is to run a heat-producing CO2 generator, such as a propane or a natural gas CO2 generator, at night. This will elevate your night temperatures to prevent condensation from forming and store up CO2 in the air for daytime photosynthesis. An important bonus for keeping your day and night times similar (within 5 degrees) is that you will reduce stretching and increase branching. The difference between the average daytime and nighttime temperatures is referred to as DIF and is an area of active research.
Reference a relative humidity/temperature chart such as the one below. The goal is to stay within a range that allows plants to transpire properly (essential for nutrient uptake) while avoiding stressing the plant or risking fungal infections.
3) With LEDs, your plants will need less water.
Exactly how much less will depend on your plants, pots, media, temperature, humidity, air circulation, etc. If you’re growing in soil or coco, remember that plant roots primarily want moist not wet. Wetness can contribute to low oxygen levels and root rot.
4) With LEDs, your plants will need less nutrients.
Experienced growers have found that they use as much as 20-30% less nutrients growing under LED than when growing under HPS. While you can achieve this by simply adding less nutrients to your fertigation, you can, alternatively, water with pure H2O every 1 to 3 times you water.
Some growers also find that adding a calcium and magnesium supplement can be beneficial for plants under LEDs due to their lower transpiration rates.
Don’t forget to check your runoff PPMs to avoid overfertilizing. Remember, the dry weight of your plant is mostly made out of carbon absorbed from CO2 in the air, not from the fertilizer you give your plant. Overfertilization is one of the most common mistakes new growers make.
5) With LEDs, you’ll keep more terpenes and aroma compounds.
Terpenes are organic compounds that contribute greatly to the aroma of plants. Heat them up too much, like under HPS lights, and much of that desirable aroma will simply drift away. Use LEDs and you’ll keep more of the aroma and flavor you want.
6) With LEDs, you can provide limitless light recipes and regimes to elicit photomorphogenic and photoperiodic responses.
LEDs have so many growers excited because you can easily adjust the spectrum to trigger a number of highly desirable traits – more branches, more flavor, more medicinal potency, more blooms, more growth. With ChilLED, it’s as easy as pressing a button on the Guardian Touchscreen Controller Interface and you send a command to your plants to grow the way you want. That’s power!
Learn more about light’s effects on plants. Also, read about UV-A’s effects on plants.
We hope that’s helpful. If you have other tips, please don’t hesitate to share them with us in the comments below!
Chris Rasmussen says
Since shifting from 315 CMH to X5 600 LED’s I have noticed my garden consistently starving.
Thus requiring much more nutrients.
The average slurry tests using NFTG Line on CMH lights was 380 – 425ppm.
The average slurry tests identical nutrients/dosing results 175 – 200ppm utilizing the X5 LED lights.
I discussed this situation with fellow growers those using high efficiency LED’s were required to increase the nutrient level to prevent starvation.
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