High Efficiency Lighting for the Farm: Part 1 - Light Sources

Discussion on choosing the best light source for you by reviewing typical lamp types and performance.
High Efficiency Lighting for the Farm: Part 1 - Light Sources - Articles

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So, you've been to the store lately, and you see all kinds of new "energy efficient" lighting advertized for sale. They sure look good on the shelf, but will these new things actually work and save you money on the farm? The answer to the question is "probably". In fact, lighting is often one of the easiest and most cost effective ways to reduce energy use on a farm. Recently, the American Society of Agricultural and Biological Engineers updated its lighting standard, and USDA has released rules of its own for lighting systems, which has added to interest in the topic. In this first part of a series of articles, we will take a look at some of the new lighting products on the market: LEDs and High Efficiency Fluorescents. Then we'll finish up by discussing some of the things to look for in a high efficiency light source.

LED Lighting

LED lights are the big "new thing" on the market right now - white light emitting diodes that turn on instantly, work well in low temperatures, and have higher efficiencies than in the past. If they are well built, they are rugged and last a long long time (claims have been made that they can last 75 to 100 times as long as a traditional incandescent lamp). Most stores have LED "replacement" light bulbs that screw into a standard socket and promise things like "60 watts of light for 13 watts of power". What they mean is that their product consumes 13 watts, but produces about the same amount of light as a 60 watt incandescent bulb. Right now, the efficiency of LED replacement lamps is about the same as that of compact fluorescent lamps - you can check by comparing the "lumens per watt" of the various bulbs on the market. The "lumen" is the measure of light output, so more lumens per watt means higher efficiency. LED lighting has been steadily improving in efficeincy during recent years, and experts expect that more improvements are still to come.

High Efficiency Fluorescent Lighting

I have seen many farms that use 8 foot long 1.5 inch diameter "T12" fluorescents. They are an older style of fluorescent lamp that works well, but is not as efficient as the thinner "T8" or "T5" lamps that are now available. The designation "T12" stands for "T-tubular shape" and "12 - twelve eighths of an inch in diameter". You can see, then, that a "T8" is one inch in diameter, and a "T5" is five eights of an inch in diameter.

It's interesting to note that, technically speaking, most white LEDs on the market are actually fluorescent lamps. The way they work is that the solid state LED produces blue and UV light, and a phosphor ccating on the LED "fluoresces" - transforming a portion of the blue and UV radiation into red and green radiation, forming a mix of colors that we see as "white".

Choosing a High Efficiency Light Source

When looking to upgrade, the first thing to look for is the "efficacy" of the light source. This is measured in units of "lumens per watt", and higher values indicate higher efficiency. Keep in mind, however, that efficiency is not the only thing that matters. Lamp life, cold weather performance, and dimming over time (lumen depreciation) and color rendering are all things to keep in mind as well.

Lamp life can vary from as little as 750 hours to 50,000 hours or more. How often do you want to be changing that light? How much will it cost? If the luminaire is in a cold location, you may need a special "cold weather ballast" (in the case of fluorescents) to make sure it operates correctly. And, don't forget that light sources tend to slowly grow dimmer as they age (I hope that's not the same for people, but you never know).

The ability of a light source to show different colors is measured using something called a "color rendering index", that ranges from 0 to 100. Incandescent lamps are the highest, with a CRI of 100. osphors used in the fluorescent lamp. LEDs usually have pretty high CRI values. Many farm areas do not need high color rendering light sources, but if your are sorting or grading fruit, vegetables, or other products, it is best to use light sources with a CRI of at least 80.

Typical Lamp Types and Performance (from ASABE Lighting Standard)
Lamp TypeTypical Efficacy
(lumens/w)
Lamp Life
(hrs)
CRI
Incandescent11-20750-2,000100
Halogen18-252,000-3,000100
White LED50-10025,000-100,00070-90
Tubular Fluorescent75-9815,000-20,00070-95
Compact Fluorescent50-8010,00080-90
Metal Halide60-947,500-20,00060-80
High Pressure Sodium63-12515,000-24,00020-80

That's it for now. Next time we will look at upgrade options and common pitfalls when selecting and designing lighting systems for farms.

See part 2:

High Efficiency Lighting for the Farm - Part 2