Solid state lighting, namely light-emitting diodes (LEDs), are completely revolutionizing indoor and outdoor lighting. Here’s why:
- White LEDs on the market today have a system luminous efficacy ranging from 50 (least efficient) to 80 (average) to 140 (most efficient) lumens per watt. This far exceeds the luminous efficacy of incandescent (5-35 lumens/watt), and generally exceeds compact fluorescents (45-60 lumens/watt). Prototypes of the next generation of white LEDs have luminous efficacies up to 150 lumens/watt, and theoretically 200-250 lumens per watt may someday be achievable. Since the traditional white light source of choice for outdoor lighting has been metal halide with a luminous efficacy of 65-115 lumens/watt, white LEDs are well on the way towards replacing metal halide. Even the more efficient orange high pressure sodium (HPS) lights, with an efficacy of 150 lumens/watt, are nearly matched by the best white LEDs. Only monochromatic low-pressure sodium (LPS) with an efficacy of 183-200 lumens/watt will give more lumens per watt than the best white LEDs.
- White LEDs last much longer than other light sources: 50,000 to 100,000 hours (between 12 and 24 years, operating dusk-to-dawn 365 days a year). In comparison, high pressure sodium typically lasts about 5 years, and metal halide a little less at 4 years.
- Unlike high-intensity discharge (HID) sources such as metal halide, HPS, LPS, and mercury vapor, white LEDs are “instant on / instant off” with no warmup time to full brightness, so they can be switched on and off as often as you like with no shortening of bulb life; and they are easily dimmable. LEDs will render dusk-to-dawn lighting a questionable option rather than an operational necessity.
My only concern is that we finally “get it right” with LEDs instead of blindly following the “more is better” philosophy as we have with every lighting efficiency improvement in the past. Low levels of white light (fully shielded to minimize direct source glare) is the most effective and efficient way to provide adequate illumination. This shouldn’t come as a surprise, however. Think of the light provided by a full moon as we have this week.
Unfortunately, most places that is not what is happening. Light levels are increasing, as is the amount of lighting. We seem well on the way towards eliminating anything resembling a natural nighttime environment for most people. I don’t know about you, but that is not a world I want to live in.
References
DIAL (15 June 2016). Efficiency of LEDs: The highest luminous efficacy of a white LED. Retrieved from https://www.dial.de/en/blog/article/efficiency-of-leds-the-highest-luminous-efficacy-of-a-white-led/.
Kyba, C., Kuester, T., et al. 2017, Science Advances, 3, 11, e1701528