In this article, we focus on efficiency (the ratio of lumen output per watt consumed by a fixture) and other benefits and drawbacks of LED use. For a quick glance at the overall efficiency comparison, consider the chart below:

You'll notice some fixture types are still very efficient in their fluorescent form, such as the 2' x 4' and 2' x 2'. (Side note: Fluorescent troffers still typically cost less than the LED version, unless dimming is desired. LED fixtures usually come standard with dim-ability and fluorescent dimming ballasts can add up to $100 to the cost of a fixture.) When it comes to downlights, it makes sense to specify LED over the sibling downlight that uses a CFL (compact fluorescent lamp). And the downlight technology is rapidly changing. The chart above is for a typical LED downlight, but some manufacturers are currently approaching the 90-to 100-lumen-per-watt mark. Another great place for LED's: high-bay luminaires. This is an area where LED technology has greatly improved recently.

Not only can LED sources be utilized in standard fixture types such as 2’ x 4’, high-bay, downlights, etc., but their smaller sizes and unique performance options also allow for quite a variety of installations. Large and small coves, cabinet details and display shelving can all take advantage of the smaller sizes and ease of installation in spaces that simply cannot accommodate other lamp sources. LED sources can also be used in exterior/wet locations within small concealed spaces, which most other lamp types cannot. These can be used for signage lighting, façade lighting and general architectural detail lighting. Below are some examples of current fixture trends in LED lighting.

Increase in number of options within the LED downlight family (aperture sizes, beam spreads, color temperatures, outputs, square trims, adjustability, wall wash):

Cove/tape lighting:

Under-cabinet lighting:

Outdoor, low-profile linear grazers:

Linear pendants (great optics with LED, providing better distribution than fluorescent):

2’ x 2’ and 2’ x 4’ troffers (catching fluorescent in cost, especially when dimming is desired):

Decorative (small pendants or unique pieces requiring low-profile sources):

Task lighting (low profile, sleek pieces):

                              Sonneman                                                            Luceplan

Another benefit to LED’s can be their color temperature and color rendering. Incandescent lamping has a color temperature around the 2500K mark, creating a nice warm yellow tone. It also has a color rendering index of 100, which means it renders colors exactly correct. Fluorescent and metal halide have relatively high color rendering (around 85) and come in a variety of lamp color temperatures for the application; however, metal halide is more limited in what it can provide for the warmer colors. LED sources vary widely in both color temperature and color rendering based on the manufacturer. It is very important to pay attention to these values or you could end up with a very blue space (blue is a much easier color for LED lamps, whereas white and the warmer oranges utilize more complex, more costly technologies). Reputable LED manufactures can produce 2500K (warm) and 85+ CRI lamps, which stand the test of a residential kitchen or retail environment—both among the most demanding environments when it comes to color rendering.

It is also important to consider that LED’s require the use of a driver. Drivers are usually small and can be located in a remote location from the LED lamping, however, given the small sizes of the LED lamps themselves, sometimes these drivers can be difficult to conceal when locating the LED lamps within a small, confined space. Consideration must be given for the installation of the entire fixture, including the power source.

The life of an LED lamp source can be a huge advantage, especially in difficult-to-access locations. However, despite some industry claims, LED lamp sources do not last forever. They are tested for their “lamp life” just like any other lamp and they do fail over time. Their failure is generally characterized by reduced light output versus the abrupt popping sound you hear in traditional bulbs, in which the mechanism actually breaks and is rendered useless. LED lamps do typically last much longer than their fluorescent and metal halide counterparts, however. Fluorescent and metal halide can last up to 20,000 hours, whereas typical LED lamp life is in the 100,000-hour range. To put that in perspective, a typical fixture in a facility operating 16 hours per day and utilizing fluorescent lighting would last for three and a half years, while an LED lamp source in the same facility would last for 17 years.

Overall, efficiency of LED's continues to increase, while efficiency of fluorescent and metal halide fixtures have somewhat plateaued. As the technology continues to develop, it is important to know what to consider when specifying new products. LED's are beginning to take the place of fluorescent and metal halide lighting more and more, and it does in fact appear that LED’s will live up to their hype as time progresses.
 

This blog entry was guest written by Jon Brooks, P.E., LEED^® AP BD+C, Principal at Architectural Engineering Design Group, Inc. Jon helped found AEDG, Inc. in 2004. He provides the expertise and coordination commitment required for lighting, power systems and sustainable systems. Jon has had the opportunity to work on a number of LEED^® certified facilities, which has increased his awareness of energy-saving strategies, even when projects are not seeking LEED^® certification. He is dedicated to maintaining an up-to-date knowledge base on ever-changing electrical technologies and standards in order to provide the most appropriate solutions for the specific project and owner.