the night skyline of a city

The use of light at night is increasing around the globe. Whatever else we might say about it, this trend is likely to continue as the Earth’s population grows in parallel with GDP. Together, these human forces are stimulating the spread of electrification and its associated benefits throughout both developed and undeveloped regions of the planet. Increased use of lighting has sparked a wide-ranging set of concerns about corresponding increases in energy use, obscurity of the night sky, and potential health impacts. Unfortunately, as discussion of these issues spreads, so do many misperceptions and mischaracterizations of their technical underpinnings – and the difference between what has and has not been scientifically established is often blurred.

DOE has assembled a variety of resources on these topics, to provide accurate, in-depth information to clarify the current state of scientific understanding.


The use of light incurs a variety of potential costs. These include energy use and associated environmental impacts, potential health effects in both flora and fauna (including humans) due to the presence of light at unnatural times in the 24-hour light cycle, and increasing obscurity of the night sky. Such issues essentially began at scale with the invention of the electric lamp and have been growing at a rampant pace ever since. 


Concerns have recently surfaced over the rapid conversion to LED technologies in general illumination applications, mostly stemming from the perceived (but typically misunderstood) increased content of short (i.e., “blue”) wavelengths that can play important roles in some of the costs noted above. In actuality, the concerns being raised pertain to all broad-spectrum or “white” light sources in use today (interior as well as exterior). A key factor, however, is that the bulk of the incumbent outdoor lighting in the U.S., especially in street and roadway lighting applications, is presently supplied by a narrower-spectrum source (high-pressure sodium – HPS) with considerably lower amounts of short wavelength content.  Much of the new concern therefore arises from projected abrupt increases in short wavelength content that could be introduced to the night environment from converting such narrower-band exterior sources to white light LEDs.


A critical factor often missing in the popular discourse, however, is that LEDs bring numerous attributes to the table in addition to their high energy efficiency and long lifetimes, including an intrinsic ability to engineer their spectral content and inherent compatibility with controls. Combined, these capabilities enable many potential benefits like dimming and dynamic alteration of spectral output: features that no other outdoor lighting technology has offered in any practical sense to date. 

LEDs thereby represent a lighting source for the 21st Century.  No other lighting technology comes close to their ability to address the seemingly inevitable increases in the myriad costs otherwise coming to our global future; in fact, LEDs and associated controls may be the only practical means of addressing them.

The links below explore each of the topics touched on above in greater detail.

Learn more about Potential Impacts of LED Street Lighting on Sky Glow and Potential Health Impacts of Light at Night.