Like all other elements of the lighting market, with LEDs and lighting control technologies replacing traditional light sources and simple photocells, outdoor lighting is undergoing tremendous changes. In this article, we will look at some of the factors driving these changes, as well as the future prospects of outdoor lighting.

LEDs
Outdoor lighting applications were one of the earliest environments where LEDs became popular, along with indoor downlights. The twin features of energy and maintenance savings were the driving factor. As often occurs with new technologies, it was a few smaller players who introduced LED-based outdoor luminaires first, with the major manufacturers following within a couple years. The expansion from early walkway and bollard lights to streetlights, highway fixtures up to the stadium lighting available today followed the performance improvements predicted by the empirical relationship known as Haitz’s Law. That relationship states that the average performance of LED technology improves by a factor of 20 over a period of 10 years while the average cost decreases by a factor of 10 over that same period.

Two other factors made LED technology appealing to those responsible for outdoor lighting applications. First was the intrinsic high directionality of light, which LEDs provide. Precise control of light distribution is very important in many outdoor applications and LEDs offered the ability to put light exactly where it was needed.

Second was the white color that LEDs offered. Just like metal halide lighting and induction lighting which also was a competing technology a decade ago, LEDs provided a much wider spectral content than high-pressure sodium, which was the dominant outdoor source. Typical Color Rendering Index (CRI) for high-pressure sodium lighting is around 25 (on a scale of 0 to 100) while LEDs typically have values of 70–85. Police and security personal liked the fuller spectrum that LEDs offered over high-pressure sodium as it made eyewitness reports much more accurate—reds look red under LED sources versus brown under high-pressure sodium.

Lighting Controls
Unlike LEDs -- which have only recently begun to expand in the outdoor lighting market—simple lighting control technology has been available for years, starting with the introduction of photocells for street lighting in 1949 in the town of New Milford, Conn. In recent years, the ever more restricting ASHRAE requirements for allowable energy usage for lighting can only be achieved using controls. 

Just as with LED technology, lighting controls are rapidly evolving as microprocessors and communication technologies become smaller and more powerful. Controls (dimming) and communications are moving into the outdoor segment of the lighting market as they allow both energy savings and a way of reporting fixture status.  

Since LEDs typically dim rather than catastrophically fail, having a means of evaluating their status is important in order to determine when to replace lamps, and the ability to do that remotely via wireless or wire communications is a big plus. For the future, reduction in the cost of control and communication technologies will drive adoption, and I expect that every outdoor fixture will come with sensing and communication capabilities built in.    

One issue, which still requires work, involves implementing new universal lighting standards (at least by country) that provide for acceptable dimming levels. As is often the case, it takes a while for standards to catch up with technology advances. Being able to dim parking or street light fixtures when no one is present is one major appeal of lighting control for outdoor applications. However, what level of dimming is acceptable from a security, safety and even occupant comfort level. Unfortunately, that answer is going to take some time for the researchers, engineers and lawyers to determine. 

A second issue that will take some time to resolve is the matter of communication protocols. The range of different control protocols (e.g. DALI, DMX, Zigbee, etc.) is large and within each protocol, different manufacturers have their own versions. At this point, turf wars are still underway and it is going to take a few more years until one or two victors emerge.

Lighting and Health
By now, most people have heard or read something about the effect of blue light on human health. It is a very popular topic for scientists, medical practitioners, journalists and salespersons, all with their own differing slant and view about what the facts are. The American Medical Association has weighed in on the subject with their publication “Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting.”2 The report recommended “that communities considering conversion to energy efficient LED street lighting use lower CCT lights that will minimize potential health and environmental effects. The Council previously reviewed the adverse health effects of nighttime lighting, and concluded that pervasive use of nighttime lighting disrupts various biological processes, creating potentially harmful health effects related to disability glare and sleep disturbance.”

The US Department of Energy also has published information on the subject and tried to set out the facts from a technology point of view.  “While the AMA's guidance is intended to reduce the harmful human and environmental effects of street lighting in general, it focuses on LEDs in particular. But it's important to note that these issues are neither new nor restricted to LED technology.”3 The DOE goes on to point out that blue light emitted by LEDs are no different than light of the same power and wavelength from other sources, including televisions, phones, computer displays, etc.

Trends in outdoor lighting using LED technology have tended to favor cooler Correlated Color Temperatures (e.g. 4000 to 6500K) since the higher temperatures usually provide higher efficacy. Also the addition of more spectral content in the blue region (for both metal halide and LED sources) provides a higher CRI which is typically favored by city residents, security and police, etc. since it provides a more realistic lighting than the common high pressure sodium fixtures.

I believe the trend for outdoor lighting will continue to move from high (or in some cities low) pressure sodium to LED. Should medical research show that shifting to a lower CCT is desirable, that can be accomplished relatively easily with LED technology by changing phosphor content. However, it is important to realize that by removing blue content, the ability of a light source to provide a true representation of a scene is limited by the physics, there is no way around that. Expect to see some arguments from both sides over the next couple of years until more definitive research arrives.

Better Design
The change in lamp design will gradually improve the efficacy and return to a better design, that is, there will be no glare bombs. This trend makes sense-LED has easily become the most efficient light source available, so there is still some room to make up for the efficacy of the luminaires, and more emphasis is placed on creating better light. This trend is particularly important in street lighting because glare can be dangerous for drivers and pedestrians. Therefore, I hope to see in the marketing literature that the power curve is flatter, and more emphasis on the first thing we think of for people.