The LED Surprise

Abstract

Address correspondence to Kevin W. Houser, The Pennsylvania State University, 218 Engineering Unit A, University Park, PA 16802, USA. E-mail: khouser@engr.psu.edu Five years ago, I was skeptical about predictions for light emitting diodes (LEDs). I questioned forecasts about the expected rate of adoption, and prophecies about LEDs becoming suitable for nearly every lighting application. It seemed implausible that, in just a few more years, LED lighting solutions would replace incumbent technologies in applications as diverse as office interiors, sport fields, stage and studio, museums, and surgical operating theatres. These applications—office, sports, stage, museums, surgery, and many others— are demanding in different ways, and they seemed too different to be illuminated by one underlying technology. Offices require uniform illumination on the visual tasks and glare control at the source, within rooms that typically have ceiling heights of about 3 m. Sports lighting must also deliver uniform illumination, but the distance between the luminaire and target may exceed 150 m. Stage lighting requires the ability to project deeply saturated light distances of 50 m or more. Museum lighting requires exceptional color rendition, uniformity, and stability, and tight control of the projected beam. Surgical light heads must deliver extremely high illuminance levels of exceptional color quality, without creating unwanted shadows. To my delight, manufacturers have continued to refine, broaden, and improve all aspects of LED lighting systems. LED chips have improved in luminous efficacy, lumen maintenance, and color quality. LED drivers have become more flexible and reliable. End-use controls have advanced. Optics have been developed to harness and control the radiation emitted by LED chips. LED packages have been integrated into luminaires in thoughtful and creative ways. The industry has come a long way in a short-time, from non-compatible kits-of-parts to turn-key solutions that can be specified similarly to other lighting technologies. This isn’t to say that innovation is over, or that LEDs are a mature technology. Far from it. Most LED luminaires mimic the shapes and typologies of existing luminaires. There are still many more LED products of dubious quality than of undeniable merit. Caution and skepticism should still drive specification decisions, and this will be true for quite some time. My surprise comes from the fact that the best-in-class LED products are not just exceptional, they are also better than the fluorescent, metal halide, and halogen products that they are intended to replace. That LEDs can perform so well across such a wide range of applications is evidence of their potential to deliver on the promise of a future illuminated by LEDs.