Everyone agrees that the popularity of LEDs is on the rise, and a variety of businesses are touting the features and benefits that this new lighting technology brings to a wide array of applications. So far, lighting designers, architects, and systems contractors have learned that LEDs are an energy-efficient, low-heat, and extremely durable lighting solution. They are changing color options, creative effects, and lighting designs in venues around the world.
However, many overlook the fact that LEDs are also changing the way we measure performance. When making a lighting purchase decision, the average consumer believes that the higher the wattage, the more light is produced, but LEDs are changing this standard. How can a 2W LED bulb emit as much light as a 15W ordinary bulb but use much less power? Because of LEDs, we can no longer measure useable brightness in the traditional terms of wattage. Where do we go from here?
The lighting industry will need to clarify wattage and performance as they apply to LED usage. Until these new standards are in place, there are several other factors to consider when making informed LED purchase decisions. A new approach to measurement will affect these future decisions and the many ways LEDs can bring a significant return on investment.
A closer look at the components involved will explain LED evolution and the source of this resulting standards shift. The development of the primary component — the LED emitter, or chip — has occupied the majority of commercial efforts to bring new LED light sources to market and fulfill the requirements of specified applications. These come in countless shapes, sizes, and configurations, with a variety of packaging adapted for manufacturing and assembly. The roadmap for improvement of the LED chip (Figure 1) has been viewed as the defining factor in the evolution of LED-based products. The general theme has been, bigger, brighter, and thus better. Nonetheless, with these performance and dimensional improvements comes a host of complications that must be addressed to maintain the efficiencies and life values that make LEDs the choice for lighting specifiers. The solutions to these complications are available, and educated decisions require understanding the key components necessary for incorporating LEDs into useful lighting products.
A key component required for the integration of useful LED lighting products is the substrate and/or the mounting structure for the LED chip. These components provide for electrical and mechanical connections as well as dedicated thermal paths, assuring the lower operating temperatures that maintain the effective life of the LED. Again, there are many designs offered in the marketplace according to the application, the specific characteristics of the lighting requirement, and the environment of the LED lighting. Knowledgeable analysis is required to determine the quality and effectiveness of each design and, in fact, for an effective new design to be created in the first place.
Electronic drivers and controllers round out the list of the major component details associated with LEDs. Many driver designs have been tested and qualified in other market arenas, giving us a strong field of proven performers. As a result of ever-improving LED emitters, new drive circuits are needed that take into consideration the new electrical levels associated with high-performance LEDs. Each time a new record-breaking LED chip is developed, a whole new set of parameters is presented to the LED integrator. Although these challenges are significant, the driver suppliers continue to step up to the task and generate new products at an ever-improving rate and at very competitive costs.
A core component of the system architecture is the control mechanism for the timing and intensity matrix, which tunes the LED lighting system to each job. Most of these control systems run on standard protocols, but there is an ever-increasing movement toward new generation control protocols that will require shared visions among LED designers and manufacturers. This movement toward change is what leads to the topic of universal standards to assure that international trade in lighting follows science-based ratings for lumens and lighting patterns.
To begin to understand how lighting is measured, there must be a review of the terminology involved. The most traditional term for measuring performance is the watt. With typical light bulbs, a customer has relied on the number of watts to determine brightness. However, watts only refer to the amount of energy or power consumed, not the level of brightness, and certainly not the lighting performance. While traditional bulbs reveal a direct correlation — the higher the wattage, the brighter the bulb — this does not hold true for LEDs.
One way to measure total light output is in lumens. A lumen is fundamental unit of light (luminous energy per second). The total light output of a light bulb, or flux, is measured in lumens. The electricity usage is measured in watts. The base efficiency of the light source is determined or quantified by the number of lumens developed per watt. However, it is the directional measurement that quantifies the true effectiveness of the luminaire. This unit of measure is the footcandle or, in simple terms, the amount of light that projects to the subject area.
A major component surrounding the measurement of lighting performance is optics. Most do not recognize the role that optical technology plays in the amount of light delivered and, thus, viewable. In many cases, it is not how much light (and, therefore, energy or brightness) but where the light should be directed and focused. This leads to a discussion about one of the least understood and most overlooked technologies required to deliver the benefits of LEDs: optics.
According to Merriam-Webster Dictionary, the basic definition of optics is: “The science of sight, or of the medium of sight, i.e. light; that branch of physics which deals with the properties and phenomena of light.” This simple definition highlights the primary relationship between optics, sight, and light. Interestingly, light is described as a phenomenon. The fundamental unit of light, the lumen, is actually a rate of reception of luminous energy per second and, thus, an inherently temporal process. Even the most static scene is lit by a dynamic flow of illumination energy, traveling at the very high speed of light, continuously being scattered, absorbed, reflected, or refracted. Details, colors, and patterns can all be quantified, and their discernment measured, for a representative sample of observers to establish photometric standards. (Figure 2)
Perhaps the most critical aspect of luminaires is how they distribute light from the lamp to the workspace. Is the lighting even? Are there enough footcandles for the visual tasks it is supposed to elucidate? LEDs are nearly point sources of light, so they are ideally suited to take advantage of the most efficient optical structures known. And because prior light sources were rarely point sources of light and usually had large glass envelopes, many types of optics could not be applied, but now such novel optics can be developed to create the uniform and homogeneous light output necessary for indirect lighting application.
The use of optics allows highly collimated light, enabling greater directional control. Optics also can redirect collimated light into a variety of patterns and create increased use of multi-color mixing by lighting designers with visionary imagination. The application of optical technology with LEDs proves that the elements of brightness can be less effective than the perception and shape of light.
By using LEDs, designers get the performance without the high energy bill. Longer lifespan and reduced energy consumption and maintenance costs allow LEDs to provide an excellent return on investment. Looking even further, the advent of the LED has helped raise an even bigger issue surrounding integration — that there are a large number of incentives and rebates available to companies that use efficient energy sources.
When a designer specifies an LED lamp instead of a conventional MR-16 halogen lamp in a project requiring 100 lamps operating 12 hours per day, the simple payback would be under 18 months. The savings over the first five years of the project would be more than four times first costs. A properly designed LED would last at least 12 years in this application, giving the user total savings of over 10 times the first costs. Additional savings would result from the reduction of 2kW of electrical demand and one half ton of air conditioning per hour.
As electronic prices fall, so too will those of photometric measurement devices, so that light measurements already being made by camera phones will spread to other portable devices and become as common as temperature measurement. Within a decade, various designs for LED lighting will have accumulated an achievement record of lifetime lumens delivered, and reputations for success or failure will have been cemented. Clear and easy-to-use photometric standards that keep up with such developments will greatly facilitate the evolution of LED lighting.
John Nylander is a co-founder of OptiLED. He has been a featured speaker at key industry events, including ETS-LDI, Strategies in Light, and the SAE World Congress.