Top five questions to ask when specifying LEDs

These are the top five questions every lighting designer and engineer needs to ask before specifying LEDs.

By Mark Hand, Acuity Brands, Atlanta October 8, 2014
Learning objectives
  • Name the important factors to consider when selecting LED lighting for a facility.
  • Understand how to mitigate costs by evaluating specific factors.
  • Identify how controls can help further maximize cost savings.

Today’s challenge for lighting engineers is to deliver solutions on time and on budget, but to also achieve maximum energy savings. It is ironic that lighting, once an energy hog, is now a solution engineers are asked to specify to help reduce energy usage. Consider what U.S. Energy Secretary Steven Chu once said: “The cleanest energy is not solar, geothermal, or wind. It is the energy saved; the energy that is never used at all.”
 According to the U.S. Dept. of Energy, widespread use of LED lighting has the greatest potential impact on energy savings in the United States. Luckily, the highly efficient nature of LED luminaires, coupled with their innate ability to be controlled, makes this digitally addressable light source ideal for many uses. With increased demand for LED lighting, specifying engineers must know the details of selecting and specifying LED lighting. 
Specifying energy-efficient lighting used to be a challenge for engineers, but with the opportunity LEDs present to the lighting industry today, the task no longer needs to be difficult. While the general perception of LED lighting is it is costly, there are ways to mitigate costs with well-written specifications by making educated choices.
1. Does the value outweigh the cost?
Short answer: Yes. 
An LED lighting solution, when properly applied, can achieve better illumination for everyday living by delivering superior performance and significant energy savings. However, the perception of better illumination is that it comes at a high cost. While some LEDs are more costly, there is typically a reason. Long lifetimes, high color rendering index (CRI), tight binning, extreme ambients, lots of control, and serviceability are often the reasons for elevated prices. 
The important point about these features is that engineers can choose what types of opportunities LED lighting provides. Since LEDs typically cost more than luminaires with traditional sources, customers often expect a longer life, better color quality, better distribution, reduced energy usage, and more control.
2. What is a reasonable lifetime?
The lifetime of LED luminaires matters greatly to end users because LEDs offer unprecedented levels of energy efficiency and have an exceptional lifetime. But what exactly is considered a reasonable lifetime, given that published lifetimes are frequently exaggerated?
Lifetimes are often inflated because LEDs are assembled in fixtures and are subject to many adverse conditions. These conditions include but are not limited to a wide range of ambient temperatures, drive current variations (i.e. inrush, surge, dimming), being turned on and off several times a day, thermal shock, and a variety of vibrations.
With that said, quality LED products can last 25 times longer than incandescent products and use 75% less energy. A quality lifetime for LED lighting is based on the application. For example, for applications where lighting is on for 24 hours a day, seven days a week, it is likely that 50,000 to 60,000 hours would be a reasonable lifetime. 
3. How important is a high CRI? 
CRI is a measure of a light source’s ability to show object colors. But when specifying LED luminaires, just how important is specifying a high CRI? Not all applications have a high CRI for existing lighting, and even if applications do have a high CRI that does not mean it is needed when replacing lighting with LEDs. 
A lower CRI often means a higher lumen per watt (Lm/W). It all comes down to considering price requirements. A higher Lm/W provides a lower cost. The lower cost is affiliated with fewer LEDs, less energy used, and better total cost of ownership. While a decent price for LEDs with a high CRI is not unheard of, lower CRI readings typically provide a better cost for projects. 
Engineers should specify only what they need and not what used to exist for the CRI. Additionally, high Lm/W does not guarantee quality illumination. 
4. What does the project really need?
When specifying a new project, a number of factors must be considered to align the lighting solution with the project’s needs. For example, when considering ways to mitigate prices of LED lighting, consider how important energy savings is versus a high Lm/W. While both options are available and can exist in one fixture, the end user may not need both. 
Also, prioritize the need for extreme ambients. Projects seldom need extreme ambients unless the temperatures are dramatically hot or cold. Having extreme ambients could provide additional costs for specialized components as higher ratings require more thermal control. 
Because each application is different, make sure each application is specified individually instead of just measuring to equivalent projects. There is typically more than one option for Lm/W to meet required specs, so consider the options and select the one that is best for the application.
5. Does more control mean more money?
Initially, the use of controls with LED luminaires does mean an additional cost. However, simple controls can pay for themselves very quickly and, throughout time, produce a dramatic return on investment. The initial increase in energy savings provides a quick financial return on investing in LED luminaires with controls. Then, over time, those same controls allow LED luminaires to have even longer life, which saves money that would have been spent replacing traditional luminaires. 
LEDs are critical, as are controls. Pairing LED lighting with controls allows luminaires to perform at their highest ability. Dimming LED luminaires does not damage them, and turning the luminaire on and off does not affect their life. Therefore, LED lighting integrated with controls is a simple solution to save additional energy and to create a convenient user experience. 
From the cost to the opportunity to pair LED lighting with controls, there are a wide range of choices for engineers to consider when specifying lighting. The right solution for the application can deliver energy and maintenance savings, and enhance the quality of light.
Mark Hand is vice president of engineering – indoor for Acuity Brands Lighting. He has been entrenched for 9 years in the lighting industry in the research, conceptualization, development, and commercialization of LED luminaires.