It’s worthwhile to take a step back and reflect on the lighting revolution that we are working on. LED lighting technology was initially motivated by the promise of improved efficiency. Indeed, LEDs have demonstrated improved efficiency compared to incumbent lighting technologies in every lighting application, and still have room to improve. They are already saving massive amounts of energy and are projected to save much more.

LED lighting can also exhibit high caliber lighting performance in terms of color quality, beam distribution, light output, and long life. It’s not easy to achieve superior performance in all aspects of lighting performance simultaneously (and at reasonable cost), but many LED products have demonstrated superior lighting performance across the board and save energy.

In addition to improved efficiency and performance, LED products show no obvious, fundamental downside. They use fewer toxic and scarce materials than previous lighting technologies. They can last much longer. They can be made for very low cost, although, with some performance sacrifices. Taken together – high efficiency, long life, reasonable cost, superior levels of performance, and new levels of control – LED lighting is clearly a once-in-a-generation (or even once-in-a-century) success story. In fact, the transition from conventional electric lighting – incandescent, fluorescent, and HID – to LED may be as a big of a shift as the transition from gas and candle lighting to electrical incandescent lights a century ago.

LEDs have also demonstrated that they can be precisely tailored and, in some products, actively controlled, in terms of intensity, spectral power distribution and optical distribution. This enables a deeper consideration of the total lighting system. By considering the LED source, the architectural space, and the human eye as a unified system, LEDs will lead us to even further energy savings. Within the lighting system consideration LED technology will enable new lighting form factors, layouts and building integration techniques, as well as new computational tools for predicting and optimizing lighting placement, optical distribution and color for a given space and activity.

LED Lighting savings projections graph
LED lighting is projected to save about 5.1 quadrillion BTUs (if DOE efficiency targets are met) in 2035, which equates to about $50B in energy cost. Source: DOE 2018 SSL R&D Opportunities.

The lighted space (room or area) affects the light coming from the light source and how human see things and experience the space. The space can change the intensity, angular distribution, and color of the light emitted from the light source on its way to reaching the eye. It has been estimated that only one photon out of a million that come out of a typical light source reach the eye. The rest are absorbed in the space. We can do a much better job of predicting and optimizing the impacts that the lighted space have on the emitted light and how it’s delivered to the eye. This will require not just modeling the interaction between the light source and space, but also considering new lighting form factors with a broader range of optical distributions and light output levels. In addition, we must re-evaluate what light levels, directionality and light colors could be for optimum visual performance of different tasks.

In terms of understanding the eye’s responses to light, there have been great strides, particularly in understanding non-visual responses to light that can greatly impact human health. From an energy-savings perspective, it is critical to understand how effectively light is being delivered and how effectively the light intensity, spectrum and distribution achieve the desired visual and non-visual responses. LED technology is a great tool for updating our basic understanding of vision science and then applying this new understanding.

Lighting application efficiency

This concept of considering the source, optical delivery, spectrum and intensity together for a given space has been labelled “lighting application efficiency” by the DOE Solid-State Lighting R&D Program. It’s great to generate light efficiently, but we shouldn’t waste it by putting it in the wrong place with the wrong color and intensity. This concept is not just an energy-savings consideration but also an important lighting design mindset. Lighting professionals do think about this, but the new levels of precision control offered by LED technology require more intense consideration of this topic.

intensity effectiveness chart
Energy savings is a function of light source efficiency, optical delivery efficiency, spectral efficiency, and getting the right intensity, or “intensity effectiveness.” Source: DOE 2018 SSL R&D Opportunities.

Thinking in terms of lighting application efficiency works for any lighting application. LED roadway lighting has long demonstrated that it can deliver required illuminance levels with less total light, achieving energy savings even at the same or lower source efficacy as legacy lighting. This doesn’t just save energy. Reducing the total amount of light and improving the optical delivery will also reduce ecological impacts of light at night.

For horticultural lighting different receptors than the human eye must be considered, the plant response to light is key to productivity. We have probably all seen the magenta horticultural lights that are believed to have a better spectral efficiency with the plants’ light response. Optical delivery efficiency is also an important consideration for getting as much light as possible to the plant, even as it grows and the leaves may change shape. Getting the intensity right is also critical. Too much light can cause detrimental effects like tip burn, and too little results in slow growth.

In architectural lighting, optical distribution and spectrum can complement LED source efficiency to save energy and provide more effective lighting for people. The lighting can be optimized to highlight a surface with a color chosen to maximize contrast. Or the lights could be tuned to provide good visual acuity simultaneously with a non-visual stimulus.

Any lighting application can be optimized by considering the source, space, and detector as a system. This will lead us to new lighting form factors, layouts, and building integration techniques, as well as new computational tools for predicting and optimizing lighting placement, optical distribution, and color for a given space and activity.

So, LED lighting source efficiency, as impressive as it is, is just the tip of the iceberg in terms of the impacts of the technology. Just as incandescent lighting changed how buildings are built, improved health and safety, increased productivity, and saved energy; with fully optimized LED technology we will see similar impacts at similar scale.

Morgan Pattison

About Morgan Pattison

Morgan Pattison is founder of Solid State Lighting Services, Inc., a consulting firm focused on the technology and application of LED lighting. Through SSLS, Pattison acts as senior technical advisor to the US Department of Energy Solid State Lighting Program and is lead author of the annually updated DOE SSL R&D Opportunities document. Morgan earned a PhD from the University of California, Santa Barbara with thesis research on gallium nitride micro-cavity LEDs.

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