Make the Switch to LED Lighting in Horticultural Applications [Part 2 of 2]

In our previous post, we talked about why light emitting diodes (LED) lighting should be used in horticultural applications instead of high intensity discharge (HID) lamps. Some experts in the greenhouse field are already calling this “a monumental shift.”

There are five key properties that contribute to the advantages of LEDs compared with traditional HID light sources. We covered the first two properties, output intensity and efficiency, in our previous article. In this post, we’ll explain the the other three: light quality, lifespan, and physical and environmental impact.

If you’re looking for more information on this topic, you can read more about the future of LEDs in horticultural applications here, and you can read more about each of the five properties below in the “Advantages of LED Lighting in Horticultural Applications” app note.

Light Quality of LED vs. HID Lighting

The key advantage of LEDs in relation to light quality is their ability to adjust and optimize the total light spectrum. This can be used to not only enhance and improve photosynthetic efficiency and control developmental phases, but also to reduce the amount of wasted light and therefore energy.

Because of their monochromatic output, a number of LEDs with different wavelengths can be used to configure light “recipes” specific to species, cultivars, and growth phases. This is opposed to HID sources that have a fixed output spectrum, which supply sufficient quantities of light in some wavelengths while providing excessive or deficient quantities at others.

Additionally, the light recipe cannot be modified to suit a plant’s development. There are currently a number of projects that use feedback control to optimize the light recipe (and other parameters) to the growth stage of plant. These systems use cameras, usually in the visible or infrared spectrum.

The ultraviolet region (UVA and UVB, 280 to 400 nm) is currently a very interesting topic in horticulture. Sunlight consists of 9 % UV (percent of PPF), while HID sources emit a fixed level of 0.3 to 8 % UV radiation (percent of PPF). With LEDs, it is very easy to control the level of exposure. Deficient levels of UV can interrupt development in some plant species. HID sources have minimal far-red radiation (710 to 740 nm), which LEDs are capable of efficiently generating. You can learn more about the importance of far-red radiation here.

Lifespan of LED vs. HID Lighting

When operated at appropriate temperatures (i.e. well below the maximum operating temperature), LEDs can last for up to 60,000 hours, which equates to 20.5 years when operated for 8 hours a day. For comparison, metal halide (MH) lamps can last only between 6,000 and 20,000 hours, or (at most) 6.8 years when operated for 8 hours a day.

The lower the operating temperature, the longer the lifespan of LEDs. In their lifespan, LEDs can drop to around 70 % of their luminous output. However, this is highly dependent upon operating temperature.

Because of the relatively high investment needed to replace LED fixtures, some believe LEDs will be operated to the limit of their lifespan despite the lower PPF in the end-of-life period (like HID lamps). Replacing individual LEDs is prohibitively expensive and impractical in the field.

However, the LED is often not the limiting factor. Power supplies, fans, and other components (such as sealings, fixtures, or enclosures) in LED fixtures can fail well before the LEDs themselves. It is therefore important for any LED fixture fabricator to ensure the supporting electronics for the LEDs are designed with reliability in mind, operating well within operating limits to maximize the lifespan of the fixture to match the lifespan of the LEDs.

Physical Properties & Environmental Impact of LED vs. HID Lighting

There are countless benefits of LED lighting when it comes to physical and environmental impact.

The small size of LEDs and their fixtures, in combination with their low operating temperatures, allows them to be positioned in places where HID sources cannot (such as intracanopy lighting); it also means there is no risk of burn injuries to operators.

Their low operating temperature also allows LED fixtures to be fully or partially encased, so they can be water and/or dust resistant. Because of their fabrication, LEDs are also significantly more resistant to shock, meaning less risk when handling or transporting lamps and fixtures. Additionally, the fabrication of LEDs does not use glass, which can be easily damaged and cause injury.

Unlike HID light sources, LEDs are RoHS compliant, which means they do not contain mercury that necessitates specialized disposal. In addition, they do not generate UV wavelengths (unless specifically added), as HID lamps can do if damaged. Because LEDs can be operated close to the canopy with a smaller emission pattern, and because they only emit the specific wavelengths used by plants, they produce much less wasted light and therefore reduce energy electricity use.

As you can see, the performance of LEDs has increased enormously in recent years. When operated at an optimal temperature, with a well-designed power supply and an optimized spectral output, not only can LED light sources compete with HID light sources, they will actually surpass them in the near future.

So where can you find products to support LED lighting in horticultural applications? Right here, of course!

Wurth Electronics offers the WL-SMDC SMD Mono-color Ceramic LED Waterclear range of LEDs. The WL-SMDC range has been expanded to include wavelengths of 450 nm (Deep Blue), 660 nm (Hyper Red), and 730 nm (Far Red), which have been optimized to match the absorption spectra of photosynthetic pigments.

In addition to the existing products in the WL-SMDC, WL-SMTC, WL-SUMW, and WL-SIMW, a diverse range of combinations is possible that can be catered to the target cultivar. Please contact us if you would like to learn more!