Published 01/12/2012

Simplifying Light

A new web-based calculator takes the guesswork out of greenhouse light management.

As Roberto Lopez helped more and more growers working to better understand and manage light in their greenhouses, a light bulb came on: There had to be an easier way.

Working with graduate student Christopher Currey, Lopez, an associate professor and floriculture Extension specialist at Purdue University, quickly approached Brian Krug, an Extension assistant professor at the University of New Hampshire Cooperative Extension.

Krug, who has already developed GROCALC, a collection of three web-based calculators (ALKCALC, FERTCALC and PGRCALC) for greenhouse growers, immediately saw the potential in building a tool to give growers the answers to one of production’s most nebulous factors: light.

“We want to take the guesswork out of production for growers,” he says. “We’re helping them speed up their processes.”

Why DLI?
As research at Purdue and other universities is showing the economic benefits of monitoring and managing light, growers are moving away from foot-candles or lux as the preferred measuring units and adopting daily light integral (DLI).

Foot-candles and lux are only a measure of light visible to the human eye. Growers are interested in measuring photosynthetic light, which is in micromoles per m2 per second. But, this is still an instantaneous reading, and light levels are constantly changing. That’s where DLI comes in.

DLI is the cumulative amount of light a plant receives over the course of a day. Think about light as you would rainfall. We record how much rain falls over a 24-hour period (DLI). How wet you get depends on how hard it’s raining (light intensity) and how long it rains (duration). Of course in the color industry, hundreds of varieties are grown, and “one size does not always fit all” with plants and light.

Simply put, DLI is a cumulative measure of light over the course of the day — and thus a more accurate way to determine how much photosynthetic light crops are getting.

To put economics behind it, using DLI could help reduce rooting time, increase quality and decrease energy costs.



Lopez, Currey and Krug aim to make that implementation easier for growers with the development of DLICALC, the fourth in the University of New Hampshire’s GROCALC web-based calculator package, which also includes ALKCALC, FERTCALC and PGRCALC.

By using DLICALC in conjunction with target DLI, you will get a more exact measure of supplemental light and more efficient use of equipment. So, for example, you aren’t running your lamps longer than you need to or, conversely, aren’t running them long enough to meet your target DLI.

If you don’t have an environmental control system that can manipulate DLI, you can use DLICALC to predict how long you should run your lamps. You could add potential energy savings to the list of benefits DLICALC provides by giving guidelines on when lamps or shade should be used....

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