The LED Lighting Revolution

Solid state lighting, namely light-emitting diodes (LEDs), are completely revolutionizing indoor and outdoor lighting.  Here’s why:

  1. 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.
  2. 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.
  3. 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-ledsthe-highest-luminous-efficacy-of-a-white-led/.

Kyba, C., Kuester, T., et al. 2017, Science Advances, 3, 11, e1701528

Two Predictions About Outdoor Lighting Technology

Here are my (ever hopeful) predictions about the future of outdoor lighting technology.

(1) Dusk-to-dawn lighting will soon become a thing of the past.

Ever see the irony that as outdoor lighting efficiency has greatly improved over the last several decades, we have moved from “light only when you need it” to “lights on all night long”?  An incandescent light, if operated less than 3 hours per night, will use less energy than even the most efficient light source operated dusk to dawn.  Yes, that’s right.  Three hours of incandescent light (which is horribly inefficient) each night throughout the year uses less energy than an LPS, HPS, Metal Halide, or LED source of comparable lumen output operated dusk-to-dawn.  Just think of the energy savings we could realize by using an efficient light source that is used only when it is needed!

Passive infrared (PIR) switches, which are rather prone to false triggering, will be replaced by image analysis software that will do a much better job of deciding when a light needs to be on and when it does not.

The HID (high intensity discharge) light sources in common use today such as HPS (high pressure sodium) and metal halide have two drawbacks.  They prematurely age if you frequently turn them on and off, and they take a while to reach full brightness after having been off for a while.  These drawbacks do not exist with efficient “instant on” sources such as LEDs, which are even dimmable.

These new technologies in lighting and control will make it both easy and affordable to have reliable light only when it is needed.

(2) Security lighting will soon be replaced by much better crime prevention technologies.

Soon, flooding a premises with light will be one of the WORST things you can do to deter and prevent crime.  As security systems improve and become more sophisticated and affordable, security lighting will only be needed when an intrusion is detected, and maybe not even then if you want the perpetrator to be detected without them knowing they have been detected.  Fixed visual recognition systems or even mobile peripheral devices (MPDs)—as Bill Gates likes to call “robots” to avoid all the anthropomorphic connotations—that operate with ambient light (visible, infrared, etc.) will soon obviate anything so primitive as security lighting. And, if the stationary or mobile sensing device is inactivated by a hostile (or non-hostile) event, its connection with the base station inside the home or business would be broken and appropriate action could be immediately taken.

As both lighting technology and lighting control technology improve, it is my hope that dusk-to-dawn lighting will be rendered obsolete.