Urban Sky Glowis the brightening of the night sky (the “glow” effect) over inhabited areas; even in an unlit area, the “glow” effect from distant populated areas is visible. This light that escapes up into the sky is created by the combination of all light reflected off of what is being illuminated, from all of the badly directed light in that area, and from that light that is scattered (redirected) by the atmosphere itself from reaching the ground. This scattering is very strongly related to the wavelength of the light when the air is very clear (with very little aerosols). Rayleigh scattering dominates in such clear air, making the sky appear blue in the daytime.
Light trespass — light falling where it is not intended, wanted, or needed. Street lighting, for example, should light streets and sidewalks, not shine into peoples’ bedroom windows or illuminate rooftops or tree branches. Also known as spill light, light trespass occurs whenever light shines beyond the intended target and onto adjacent properties.
Below is an image of houses in Grainger Indiana that are irradiated by the newly installed lights of the nearby baseball fields of the Harris Township Junior Baseball and Softball Association. Officials had said that the new configuration would spill light that is equivalent to a full moon, yet it is many times stronger. Does anyone really believe that the owners of the houses shown are happy with the new lights and the interruptions of their sleep?
Glare — the sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to. It causes annoyance, discomfort or loss of visual performance, visibility and can be dangerous. High levels of glare can decrease visibility for the elderly, drivers of motor vehicles and astronomers. It is easily recognized by when a viewer’s pupils will close down in its presence. This makes dimmer objects harder to see, and that increases the danger.
Here, a brightly lit entrance to a West Boynton HOA blinds drivers trying to find the entrance:
Here a student crosses a crowded parking lot while the driver has to contend with the light at the end of the parking lot. Add a drizzle of rain, and someone’s need to hurry and we have the makings of a tragic accident.
The parking lot on the left exemplifies shielded lighting. Note how few lights are needed to illuminate the area and how it is done without glare. The photo on the right shows lights shining into the sky and creating painful glare. It’s hard to say whether the business owner is trying to attract customers or cause a traffic accident, there are so many poorly aimed lights being used.
Image Credits: International Dark-Sky Association
Which parking lot do you think people will feel is more comfortable, more welcoming, and less oppressive to drive into?
Uplight — wasted light, pure and simple. Light that goes directly up into the night sky is “lost in space” and serves no useful purpose (though the most often used for self centered vain purposes). Uplight is the bane of astronomers and the occasional stargazer because atmospheric scattering artificially brightens the night sky, making distant celestial light sources difficult or impossible to see. Uplight often results from light fixtures which also produce glare and light trespass.
See also Adam Kuban’s example on the Economics page of wasted uplight.
Clutter — bright, confusing, ugly and excessive groupings of light sources, commonly found in over-lit urban areas. The proliferation of clutter contributes to urban sky glow, trespass, and glare.
Businesses that compete against one another often try to outshine each other. This leads to a one-up-man-ship war that simply hurts all. Note how the clutter basically de-emphansizes each store and turns the view into an offensive, ugly, and blinding mess.