Looking from up there

One needs to be an astronaut to enjoy a view like one on the left, Florida from the Space Shuttle.
However, most of us have contemplated similar views during airplane takeoffs or landings. The view is fantastic, thousands of city lights shining like stars on the ground, outlining the roads and neighborhoods. But one has to go a little bit further than that and think. Should you see those lights at all? Is there any use of the light that you see, light that obviously goes up, other than illuminating bird and airplane bellies?

Light stands for Lighting

We all know why we have light outside. Outdoor lighting is used to illuminate roadways, parking lots, yards, sidewalks, public meeting areas, signs, work sites, and buildings. It provides us with better visibility and a sense of security.
People sleep better when their property is properly lit, when their car outside is clearly visible through the window. However, light alone does not provide security, but a sense of security. Unless you're up all night, nothing guards you better than a barking dog, a fence/door/window security system or neighborhoog watch/police patrols in your neighborhood.
When well designed and properly installed, outdoor lighting can be and is very useful in improving visibility and safety and a sense of security, while at the same time minimizing energy use and operating costs.
BUT, because nobody thought of this, most street lights shine light not only on the nearby ground, where IS NEEDED, but also miles away and skywards. Thus a large fraction of the light is lost, at consumer expense and without his/her consent. 100% pure waste. Paid for by you and me.

Most of the wasted light in cities comes from the POORLY DESIGNED STREET LIGHTS. Billboards, decorative lights, glary gass station lights, poorly shielded security lights are part of the problem too, but the main culprit for the waste and ugly glow one sees above one's head at night comes from streetlights.

BAD AND GOOD LIGHTING

The definitions are simple.
GOOD LIGHTING is a properly shielded light, that illuminates the sidewalk, your yard or your property. In the you have control over outdoor lighting, like security lights, you're showing RESPECT for you neighbors privacy by keeping the light in your yard.

BAD LIGHTING is a light that leaks light sideways or upward, as most of the commonly used street lights are. Also, most of the security lighting people install in their yards shines brightly on neighboring properties. Letting you yard light shine on your neighbor window or yard is rightly qualified as LIGHT TRESPASS in some states or counties and one could get a fine for an offending light.

To learn more about lighting and how to be a good neighbor, see New England Lighting Advisory Group's online publication, GOOD NEIGHBOR OUTDOOR LIGHTING.

But since the street lights are the main problem, I will mainly talk about them.

The part of a illumination device that decides where the light goes is the head of the lamp, called the fixture. The Cobra-Head design, pictured below, is the most widely used fixture for public illumination, although it produces huge amounts of upward and horizontal spill. You may wonder what's wrong with the horizontal spill. The horizontal spill reaches the ground half a mile or more from the lamp. At that distance, the intensity of the light has decreased to 0.2% of the intensity straight below the lamp. You see the lamp from half mile, but it doesn't help you see the things around you. It's like an airplane headlight in your eyes. It's only glare.
From the efficiency point of view, for a typical pole of height around 25', any light that goes less than 15 degrees with the horizontal will produce inefficient lighting. Thus, any practical design should cutoff light that shines less than 15 degrees with the horizontal.
Light that glares in your eyes will not improve your vision, it will most probably impede it.

In order to recognize the good fixtures, it's good to know what's available out there. I went to Baltimore Gas and Electric's own web site and browse the options. Here's what I found.

BAD FIXTURES

Flood Light
If used as in the picture.
30-50% light goes upward
If pointed down
Zero light loss.
photo © BGE

Decorative
~70% upward
photo © BGE

Sidewalk Light
~30% upward
photo © BGE

Cobra Head
The most used design
for street lights
Unchanged since 1960s
~30% upward
photo © BGE

Looking at the lamps above, one cannot always imagine how the the light escapes. Plus, the lamps are always being mounted during the day and usually nobody checks where the light actually goes. I will illustrate what I've just said with some examples. During a trip with the Greyhound bus some time ago, we've stopped to change the driver in a small city somewhere in Pennsylvania. Because the night was very foggy, the illumination pattern of street lamps was obvious so I stepped outside the bus and took some photos. The pictures below show mostly cobra-head lamps but you will see one flood light too. A couple of the pictures have bee taken more recently, in Baltimore. You can see more photos under GOOD FIXTURES.
BAD Two cobraheads seen from ~1/2 mile. High-pressure sodium (HPS)(reddish) photo © Alin Tolea	BAD A cobra -head in front of my former house photographed from the roof, from above the lamp. The upwards and sideways spill is visible. Too bad there was no fog outside so one can see the illumination pattern more clearly. photo © Alin Tolea	BAD One HPS and one high pressure mercury (HPHg)-greenish-, cobra-heads and a poorly shielded floodlight. With proper shielding/ reorientation the floodlight could be easily turned into a "good" light. photo © Alin Tolea
GOOD FIXTURES
Box Design Best design ever. Can have round, cylindrical or other shape head. Receded bulb Flat lens 100% downward photo © BGE	Good decorative. In campus at JHU (old lamp). Receded bulb only ~ 5% upward photo © BGE
Some Examples of good lighting

In the foreground, a box design lamp Dozens of bad cobra-heads shine in the background. Far in the background, at the photos' right, a poorly oriented floodlight. photo © Alin Tolea	Illumination pattern from a box design lamp in downtown Baltimore. Also along Martin Luther King Jr. Boulevard. All the light goes down, as witnessed by light cone on the trees. See the picture below for a wider view photo © Alin Tolea	Good lighting in bad neighborhoods I was amazed to find this full cutoff lamp among dozens of cobra-head design lamps at the corner of Barclay and 29-th st. in Baltimore. photo © Alin Tolea
	Another downtown Baltimore picture BAD Unshielded street lamps on the right side of Charles St. GOOD Two box design lamps on the left side of the image. The difference is obvious. The box design lamps have better illumination downwards and no light spill upwards as witnessed by the shadow on the tree at the image left. The Cobra-heads spill light at far distances in almost all directions. There could an explanation for the presence of both types of lamps. The more efficient, modern design, box type lamps have been requested and paid for by the nearby office buildings and hotels. The other lamps have been installed by the municipality, constrained by BGE to this old design, which the utility company probably has in stock. BGE "recommends" the Cobra head as the best design for street illumination. You sell what you have most, I guess. Looking at the photos, cobra-head is far from being the best design. photo © Alin Tolea

FROM THE ABOVE. Where is all the light going? One does not realize how much light is lost until one does not look from the above. The tremendous amount of light that is wasted from poor designed lights has been acknowledged for the first time the moment satellite imagery of the Earth at night has become widely available. One's first thought when looking at the photos below is: Oh, this is light from the cities. It's true, but the light you see below is mostly the light that leaks UPWARDS. There is of course a certain amount of light reflected by the ground, but is about ten times fainter (the average sidewalk reflectivity is about 10%) then the light which goes straight up. Thus the light you see is 90% the one that goes up...
Night fall over North America © Astronomical Society of Pacific	Daybreak © Astronomical Society of Pacific
North America at Night Defense Meteorological Satellite Photo (DMSP) Source: International Dark Sky Association (IDA) Satellite imagery © IDA	Wasted light from North America's cities The photos above witness the the color of the most common used street lamps in today's US. As one can see, bad lighting habits have spread light pollution to virtually every corner of US, even to the "dark skies" in the SW USA, place of America's main Northern Hemisphere inland astronomical observatories.

So, Why is the sky bright?

Looking at the satellite photos above one could think, ok, the light goes up and is lost in space. It is indeed wasted, and we pay for it. But is the light simply going straight to space? No it's not. Some of it returns to Earth but with little use but to obliterate stars...In order to understand where the light goes, let answer another question.

Why is the daytime sky bright and blue? The daytime sky is bright because Earth is surrounded by an atmosphere. Air molecules reflect, scatter and diffuse sunlight. Thus the sky becomes bright, the same way the air becomes bright in the front of your flashlight in a foggy evening. Dust and water vapor accentuate the light scattering. That's why the sky looks bright whitish in humid summer days and dark blue in dry winter days.
The color is a different issue. Air molecules and dust preferentially scatter blue light. If one scatters blue light, one gets bluish colored surroundings. The effect is cumulative. Thus, the miles of skies above you look blue, although the nearby you air looks transparent.

So why is the night sky bright? Light escaping from poorly shielded streetlights illuminates the air above us. Light scatters on air molecules and the sky becomes brighter. This is the reason the sky is bright even in dry, clear winter nights. Adding moisture and dust to the sky makes the situation worse. The scattering becomes terribly efficient and the sky becomes red from the light escaping HPS lamps or white from Mercury lamps.
Faint stars disappear, only the Moon and the brightest planets stars remain visible. If the night is cloudy, the light pollution effects are striking. The clouds are red and bright and one could read the newspaper using the light reflected by the clouds. So much light is uselessly pumped toward the skies that the reflected light is enough for a decent illumination. I'm fairly sure that was not the intention here... The waste is enormous. At a fraction of the cost, we could have good design lamps with lower power which can provide the same illumination.

Some private individuals and companies use good lighting. Their lighting engineers are good and well paid and they are doing their job of minimizing loss.
City municipalities lighting engineers don't recommend good lighting from obscure reasons. One of them could be that they are not doing their job of minimizing the public outdoor lighting bill. Incompetence, utility companies influence? Aliens? Stock of bad lights and contracts with manufacturers? Most probably ignorance.
The worst part is their bad advice costs us, the taxpayers, money. Big money, as we shall see. Money that get in the pocket of utility companies. So:

Light stands for Lighting

So, Why is the sky bright?

Next: How Much Does Light Pollution Costs?