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Help with heat lamp design for crop drought research


I'm designing a benchtop greenhouse experiment to study drought effects on crops. We have 24 cabbages growing in a 100 x 140 cm area. We're after a top-down warming system, suspended approximately 50cm above the crops, to warm the crops as uniformly as possible. This is to mimic the sun and cause evapotranspiration (water loss from the plants and soil). A second, equal design will have some slats between the heat source and the crops that block some of the heat.

I'm currently thinking having a few linear infrared bulbs setup.

My question is: Which type of bulb, what wattage, how many, and which fitting? We want to direct the heat to our experiment without heating elsewhere too much (e.g. neighbouring benches). Or is a different setup a better idea?

Many thanks in advance.

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April 8, 2019 07:42

IR lamps will produce heating, but aren't very good for simulating sunlight for plants. Sunlight at the earth's surface is about 1kW/sq meter, but much of that power is in the visible and uv spectrum. Photosynthesis mostly depends on light in the wavelengths around 450-475 nm and 650-675 nm (blue and red-orange light). I think you'd be better off using some of the commercially available grow lamps (some are florescent, some are LED) to address the visible spectrum and photosynthesis, and heated air (multiple options available) and perhaps soil using heat mats would produce better results.

Evapotranspiration depends on wind, humidity, and barometric pressure in addition to sunlight and temperature. It also varies depending on the type and size of plant. Remember to consider night as well as day. Evapotranspiration can be negative as temperatures drop and dew forms!

This isn't an easy experiment to do well.

(I've had some experience implementing weather stations for agricultural use.)

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April 8, 2019 07:43

Hi, that sound like a really interesting project but I have questions over two aspects of the requirements. You say
"We're after a top-down warming system, suspended approximately 50cm above the crops, to warm the crops as uniformly as possible. This is to mimic the sun ..."
If you are mimicing the sun, wouldn't this require two systems, one to control the local air temperature and one to simulate the IR radiation of the sun?
My thoughts are you may require IR heating as you described and at a power level to match the zone of the area to be simulated kW/square meter. The ambient air may then need to be controlled (cooled) to then simulate the local ground conditions?
Sorry if this is all known information, I'm just thinking out loud!
In the UK I recall sun radiation is approx 1kW/square meter so I would guess at a minimum you will be looking at about 3 of 4kW spread across as may IR bulbs as possible, but that I believe will need significant local air cooling control by controlled ventilation.
If you actually just want air heating then you could also consider heating mats which will be good in a chamber. Look forward to your feedback.

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