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Infrared Radiation

Infrared Radiation

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Plant Science Topics:

 

-Plant metabolism

-Plant response to temperature

-Leaf temperature vs air temperature

-Vapor Pressure Deficit (VPD)

 

Recommendations to Apply the Science:

 

-Lights with automatic shutoff for high temperature

-Choosing lights by heat output

-Positioning lights to consider heat

-Using fans and AC to manage heat

 

Product References:

 

-Autopilot Day & Night Cooling/Heating Thermostat

-Autopilot PX1

-Active Air 45 Pint Dehumidifier

-Autopilot Digital Environmental Controller

-Phat Fan 8”

-Phat HEPA Intake Filter, 8”

-Solar System 550

-Solar System Controller

 

 

(Golden Corral Intro, Then greenhouse lines are below)

 

Welcome to Episode 8 of plants and light, Infrared light. We are going far beyond the visible spectrum now, infrared stretches from about 800 nm all the way up to 1,000,000 nm, or 1 mm. Past that, we’d be getting into microwaves. Microwaves and infrared are both seen in heating applications. At first this seems strange given that these wavelengths are less energetic. UV light is so energetic is can penetrate into surfaces and destroy molecules like DNA. Well, infrared and microwaves don’t do that, they enter into objects and simply shake molecules around. Microwaves are able to penetrate deep into objects and rotate certain molecules creating friction, and this heats up the object. Infrared lights are absorbed faster, and don’t penetrate as deep into objects, they also don’t rotate the molecules as dramatically as microwaves, they mostly just stretch and vibrate the molecules, still generating heat.

 

As we saw in the buffet line, infrared light has benefits when used to keep food warm, but the applications in a garden are usually less obvious.

 

Let’s start in a greenhouse with high bay lighting.

 

Here we have 1000 W Double Ended High Pressure Sodium lights. These definitely emit some infrared light. And over here we have an 800 W LED light, which emits almost no infrared light. Both are very powerful lights, capable of providing plenty of light.

 

The infrared light from these high pressure sodium lights are capable of heating up the surface of leaves, like this banana. In warm high light conditions like we have here in Dallas, plants transpire a lot and this sweating can help regulate their leaf temperature. In this hot conditions, the infrared doesn’t have a big impact on leaf temperature.

 

But, most growers are using supplemental light in a greenhouse during the winter, this is when natural light levels are the lowest. And during the winter the conditions are often cold, so heating up the leaf surface can actually be a benefit. Earlier this week we had a cold front and it was 60 degree f outside, uww chilly, well in here I measured the leaf temperature of these banana leaves, one under hps and one under LED. The HPS leaf was at times almost 3 degree F warmer. Raising the leaf temperature can result in faster growth, and sometimes it’s too fast, triggering premature flowering. Each situation varies a lot. We’ll look more at the decision making process for picking a grow light in episode 10.




 

A really cool technique some growers have started using is the application of LED light during summer months in a greenhouse. At first this sounds strange, why add light during the summer when natural light levels should be plenty. I’ll explain this technique in detail in the next episode after we cover the final fundamental of horticultural light, because this technique involves all three of the fundamentals to achieve a very specific, very awesome goal.

 

Let’s look at infrared indoors, or in a grow tent. In these situations most growers struggle with high temperatures, so a light that heats leaf surfaces may not sound ideal. However, like I said earlier, plants in normal growing conditions, that are transpiring a lot, are generally able to regulate their leaf temperature fairly well. The thing is, the lights that emit infrared, generally create heat in other ways, like convection.

 

This is a standard convection fan heater, it heats the air with hot coils in there. Well the surface of grow lights get hot and they can heat the air. This is convective heat transfer. LEDs are often more efficient at producing light. They’ll generate less heat while putting out the same amount of light as a traditional lighting source. So, how can controllers control heat in their grow room, well, there’s picking grow lights that generate less heat, or fans, or thermostats, which control fans, or AC units, or air cooled hoods. And then there’s backup methods for controlling heat, like auto dimming features in some lights regulated by temperature, or emergency shut offs built into controllers when certain temperatures are reached. To see some of the cool options for maintaining a cool growing environment. Check out my cool blog, at FarmerTyler.com, Cool.

 

This has been Episode 8 of Plants and Light, in the next episode we look at the third and final fundamental of horticultural lighting: light quantity. Can you see the light at the end of the tunnel, only two more episodes left! If you haven’t subscribed yet to the Farmer Tyler YouTube Channel, well, maybe consider it. I’m Farmer Tyler, and the more you know, the better you grow.

 

B-Roll of auto shutoff.

I’d like to thank Hydrofarm for making this video possible. Excess heat can be a huge issue for growers. Here I’m demonstrating how the PX1 controller can automatically dim lights when they reach a programmed temperature, and the controller will even shutoff the lights if they reach a higher programmed temperature. This feature can easily save crops if there is an issue with your cooling system. Check out the PX1 and other tools to help you grow at Hydrofarm.com

 

 

 

 

 

 

 

 

 

 

Source:

Jacob A Nelson and Bruce Bugbee. Analysis of Environmental Effects on Leaf Temperature under Sunlight, High Pressure Sodium and Light Emitting Diodes

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0138930


 

BLOG NOTES

 

Lights that are good for delivery infrared include HPS lights. But if in an environment that could have a potential failure in environmental control, like this greenhouse, if the fans fail, this heat buildup could be damaging. This controller includes an emergency heat dimming feature, and if heat continues to rise it will shut off the lights. The positioning of the light is important too, in a greenhouse I can place the lights high above the crop to keep the heat away, but indoors this may not be possible unless the facility has high ceilings. Sometimes growers use aircooled lights to move the heat away from the lights and outside the grow. Other ways to protect from heat include exhaust fans controlled by a heat thermostat, controllers that manage fans by indoor conditions,

 

Grow lights that don’t push out much heat and Choosing lights by heat output

 

-Autopilot Day & Night Cooling/Heating Thermostat

-Autopilot PX1

-Active Air 45 Pint Dehumidifier

-Autopilot Digital Environmental Controller

-Phat Fan 8”

-Phat HEPA Intake Filter, 8”

-Solar System 550

-Solar System Controller

 

Video Production Direction:

 

-Walk through greenhouse with infrared camera, show how different lights put out different amounts of heat.

-Show Autopilot PX1 controller and ability to dim or shut off lights in response to high temperatures

-Show how fans can help manage heat




 

But, in normal growing conditions, when a plant is transpiring a lot, the plant cools itself a lot preventing the leaf temperature from rising out of control. But, in conditions of water stress, if the plant isn’t getting enough water and can’t transpire, the leaves can definitely get hotter under HPS versus LED. According to research by Jacob A Nelson and Bruce Bugbee the leaf temps can rise about 4 degrees C or 7.2 degree F higher when grown under HPS vs LED in water stressed conditions. High temps can lead to heat stress and crop damage. Heat stress can look like stretching or stunted root growth. Or just fryed up plants that are turning crispy.