LEDs are fundamentally different from other lighting technologies. Instead of using a filament (incandescent), a gas discharge to excite phosphorus (florescent) or an electric arc (metal halide), they use light emitting diodes, or LEDs as they are commonly called, to convert electricity to light through the process of electroluminescence.

LED lighting is part of a group of light sources called SSLs (Solid State Lighting) that use semi-conductors to convert electricity into light. The light is emitted from chips about one square emillimetre in area consisting of layers of semi-conducting material. LEDs have been around for decades primarily as indicator lights for equipment. Recent advances in technology, combined with the US government’s phase out of lighting technologies that do not meet minimum performance criteria, have accelerated advancements in LED performance.

All lighting fixtures convert watts to light measured in lumens. There are four costs to be considered in cost of a lighting system. The cost of ownership consists of the purchase cost, the operating cost, the maintenance costs and the disposal costs. The US Department of Energy is estimating that by 2016, the cost of ownership over the usable lifetime of LEDs will be lowest for common residential lighting applications. The current barrier to lowest cost of ownership is the high purchase cost of LED lights; however, this is expected to be lowered with new advancements. For agricultural applications, there is the future potential of widespread adoption.

The principle advantage of LEDs is their efficiency of converting electricity to light and lifespan. are shown in the table.

Table 1. Efficacy and lifespan of typical commercially available lamps

	Incandescent	Fluorescent lamp	Compact fluorescent lamp	LED
Efficacy (lumens/watts)	6 - 18	35 - 80	60 -175	19 - 76
Operational lifespan (hours)	750 - 1,500	8,000 - 20,000	8,000 - 12,000	25,000 - 50,000

^{From Benson et. al. Durability of Incandescent, Compact Fluorescent and Light Emitting Diode Lamps in Poultry Conditions. 2012. Applied Engineering in Agriculture. Data based on survey of manufacturer provided information.}

LEDs have certain properties that make them very interesting for swine producers and include directional light emission. The light is only emitted in the direction the chip is pointing, unlike a tungsten filament, which that emits light in every direction and often the light has to be reflected back to the required direction.

LEDs are resistant to mechanical failure and can survive vibrations and hits without failing. Due to the low temperatures generated, glass components can be replaced with plastics or other materials eliminating the risk of broken glass. T8 and T5 florescent tubes and ballast can be replaced with LED tubes with integral circuits to replace the external ballast.

LEDs are instant on, faster even than incandescent lights, and dimmable. They can be turned off and on repeatedly without any detrimental effect. Of particular interest to the livestock sector is LEDs' ability to mix chips of multiple types of LEDs in a single product. This can lead to a light source that is tuned to an individual species’ needs. Research has already been done to reduce aggression in chickens by altering the light colour with LED lights.

Besides efficacy, long life also is a major feature. The caution though is that LEDs seldom burn out as most lamps do but gradually fade over time. The useful life of an LED lamp is determined by its L70 rating – the estimated life in hours of the lamp when it is still outputting 70 per cent of its rated capacity. This number is the agreed upon value where most people begin to notice a difference in the light output.

Another issue is that LED lamps have lower total lumen output per lamp. There are no LED lamps currently available that can replace a 100W incandescent or a T8 Fluorescent tube and match the original’s lumen output. Producers would have to add additional fixtures to maintain the same lumen levels as before. As LEDs are unidirectional in their light output, even distribution of light can be an issue as LEDs make better spotlights than floodlights. The individual properties such as to how the lamp is designed and the placement of the chips on the lamp will determine the distribution pattern.

LEDs, unlike other lighting fixtures, do not radiate heat out from the lamp. An incandescent lamp for example uses 80 per cent of its electrical consumption to generate heat, most of which is radiated out. LEDs are actually more efficient in cold temperatures and are often used in cold storages as they do not significantly add to the heat load. The heat they do produce must be removed by conduction or convection. As with most electronics, their life is drastically reduced if overheated. Many manufactures use a heat sink material such as aluminum to transfer heat from the chip to the surrounding air.

For more information on LEDs please consult the US Department of Energy web site on Solid State Lighting [click here].

July 2013