Grow light use is, well, growing

By |  April 12, 2018 0 Comments

Sunlight is one of the holy grails of turf, one that golf course superintendents recognize as an essential element for overall turf health. Trees are the most common culprits in causing low-light conditions. There are numerous reasons why trees appeared in such abundance on golf courses, including courses that were cut out of wooded areas, trees being used as a “safety net” protecting golfers from flying golf balls from adjacent holes, and golfers and the public in general just liking trees.

Although tree removal to promote more light and air movement has become a common and accepted means of promoting turf health, there are situations where tree removal is more complicated (playing strategy, aesthetics, protected environment, etc.). In localized areas such as a putting green, some golf courses are looking at grow lights to promote more healthy turf under low-light conditions.

The lights themselves have their origins in greenhouse production. That technology was adapted for use on athletic fields — especially soccer fields in the United Kingdom and Europe — to promote growth during winter. The large grow light apparatus can cover a field or move slowly across it. This technology has been adapted by a few athletic stadiums here in the United States.

The use of artificial lights is built on a basic understanding of radiant energy and what turf requires. The first is how radiant energy is measured. Units like foot candles and lumens are associated with light intensity for human eye sensitivity and have nothing to do with plants. In the case of plants, we use the units µmoles m-2 sec-1, which is the number of photons falling on an object (photosynthetic photon flux density [PPFD]). This is the energy the plant uses for photosynthesis.

The minimum level of light required — referred to as the light compensation point (photosynthesis = respiration) — for cool-season turfgrass plants is around 40 to 150 µmoles m-2 sec-1, and for warm-season turfgrasses is around 200 to 300 µmoles m-2 sec-1. Maximum light intensity (often referred to as the light saturation point) for cool-season turfgrasses ranges from 500 to 1,000 µmoles m-2 sec-1, while warm-season turfgrasses range from 1,794 to 2,139 µmoles m-2 sec-1.

To make a point, I’ve conducted a few class demonstrations measuring the light intensity of various types of light bulbs. Shining a 60-watt halogen light bulb set 5 inches above a flat surface, I’ve measured 147 µmoles m-2 sec-1 at the surface. Not accounting for the light spectrum, this is barely enough to reach the compensation point of cool-season turfgrasses.

The light bulbs used in greenhouses or on athletic fields are termed high-intensity discharge (HID) lamps. Two types of HID lamps are metal halide and high-pressure sodium lamps. There is generally not much difference, but the metal halides tend to favor the blue spectrum while high-pressure sodium lamps tend to favor more of the red spectrum. More athletic fields use high-pressure sodium lamps because of lower cost and longer life compared with metal halide.

Conducting a similar class demonstration with a 400-watt metal halide lamp (the norm now on soccer fields throughout Europe is 1,000 watts) set 5 inches above a flat surface, I measured 1,500 µmoles m-2 sec-1. However, the temperature at the surface was 102 degrees F. Besides illumination, heat is generated from light bulbs and lamps. When I raised the lamp to 12 inches, the light intensity was 600 µmoles m-2 sec-1 and the surface temperature dropped to 84 degrees F.

Duration is important when using artificial lights, as is the relationship between desired light intensity and the height of the lamp above the turf. From an agronomic perspective, adding supplemental light is an option for greens and tees whose problems cannot be remedied by tree removal.

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