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LED or HPS? – That Is the Question

April 9, 2013

Aside from being the location for the most recent site visit in our Farm Energy Auditor Training Program, Lakewood Turkey offers an example of the use of two high-efficiency lighting options for poultry barns: Light-Emitting Diodes (LEDs) and High Pressure Sodium (HPS). In the barn that our group toured, farmer Mike Langmo is using HPS lights. Meanwhile, in the other finishing barn, he has installed LEDs and is participating in our LED Pilot Project. While each option offers energy savings over alternatives such as incandescents or fluorescents, there are both positives and negatives that poultry farmers might consider if contemplating an upgrade.

Poultry absorb a broader range of the electromagnetic spectrum than humans do

Poultry absorb a broader range of the electromagnetic spectrum than humans do

First, though, a quick overview of the role of lighting in a poultry operation such as Lakewood Turkey: There are three principle goals in the use of light – 1. letting the birds see, 2. initiating hormone release, and 3. stimulating internal growth cycles by simulating day-length. Poultry absorb a broader range of the electromagnetic spectrum than humans do. And beyond seeing with their eyes, poultry also ‘see’ with a packet of photosensitive cells in their brains, an area called the pineal gland. These tissues help regulate circadian rhythms in the birds and also influence sexual development and reproduction. Because poultry react strongly to light, farmers can encourage productive activity through lighting programs. In fact, the birds learn a particular lighting program and anticipate the photoperiod (or length of light and dark in a day), basing their feeding around it.

Turkey farmers provide higher light intensities and longer photoperiods during the first several days of poults’ lives, part of the initial ‘brooding’ period where young turkeys grow in a warmer, more secure environment. More light stimulates activity and helps them find food and water sources. After a few days, the light levels are lowered some and the photoperiod shortened to approximately 16 hours of light per day for the remainder of their time in the brood barn and also after they have moved to a finishing house. (Of course, each producer brings a slightly different approach to her or his lighting program.) These longer lighting schedules mean that more energy efficient lighting can bring significant savings.

So how do farmers decide on what lighting to employ? As the University of Wisconsin Extension puts it, “The best type of lighting is the one that provides the needed amount and type of light to perform a task or increase productivity at the minimum annual cost (operating and fixed costs).”

Finishing barn with high pressure sodium lights and one sidewall with windows open for natural light

Finishing barn with high pressure sodium lights and one sidewall with windows open for natural light

A common measurement of a light’s effectiveness and efficiency is its lumens per watt. Lumens are the amount of light a source produces. Compared to the popular compact fluorescent light, which produces 50-70 lumens per watt, HPS lights range from 50-140 lumens per watt. LEDs can offer 30-100+ lumens per watt, depending on their manufacture.

However, lumens aren’t the only measurement to note. Practically speaking, how much light actually makes it to a targeted area is of greater importance. This is often measured in footcandles – the amount of light hitting a surface – defined as the number of lumens per square foot. Here LEDs give HPS lights more competition. This is because HPS lamps cast light in all directions, due to the way they operate, and must use shields and reflectors to direct the light to its intended target. LEDs, meanwhile, are built to focus light directly where it is wanted, thus eliminating the amount of wasted light.

Another consideration that makes LED lights attractive are their long lifespan (50,000 hours versus HPS’s 24,000 hours) and a design that makes them much less susceptible to problems from dust, humidity and temperature. LEDs’ solid-state design also eliminates worries about mercury contamination should bulbs break.

Finishing barn with LEDs (turned off) and sidewalls and skylights open for natural light

Finishing barn with LEDs (turned off) and sidewalls and skylights open for natural light

Finally, HPS lights don’t stack up as well to LEDs in terms of color rendering. HPS lights give an orange-yellow light that doesn’t show colors in their ‘true’ sense, as they would look in full daylight. LEDs, on the other hand, have a color rendering index (CRI) much closer to natural light. LEDs are also easily dimmed, whereas HPS cannot be. Given poultry’s expanded sensitivity to light, LEDs can offer farmers a greater degree of control over their lighting than can HPS lights.

But LED lights are still the more expensive option, which is a key consideration for farmers facing thin profit margins and expanding costs. This higher expense and longer payback time are enough to turn many farmers away. While rebates can help alleviate such concerns, interestingly enough, the state policy underpinning utilities’ rebate programs pegs reimbursement for lighting improvements to lumens per watt. And on that metric, despite advantages offered by LEDs, HPS is the more attractive option.

So, LEDs or High Pressure Sodium? With the mixed bag of cost, rebate policies, and light performance, that is still the question.

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