How will we reduce light pollution and still have the light we desire? By following the recommendations below you can reduce, if not eliminate, light pollution with one exception: ecological light pollution. In Ecological Consequences of Artificial Night Lighting, Drs Longcore and Rich note that “Artificial light disrupts interspecific interactions evolved in natural patterns of light and dark, with serious implications for community ecology.” The solution to “ecological light pollution” is to turn lights off during the hours of natural darkness. To solve the other challenges associated with artificial lights at night:
- Select a suitable light fixture.
- Shield lights to direct the illumination well below the horizontal
- Shield every light
- Reduce the amount of light
- Select lights with a warm color
- Turn lights off when you are not there or use a motion sensor
Select a Suitable Light Fixture
Better Lights for Better Nights Handout is a great starting point to learn about fixtures that control where the light goes and therefore may be able to reduce light pollution versus those fixtures that pollute our shared sky. Notice the acceptable lights shield the source of the light from most direct viewing angles. None of the acceptable fixtures allow any light above a horizontal line drawn through the lowest point of the illuminating elements. The best fixtures cut that illumination off so that the angle made by the outer side of the illumination to the ground is even less.
Shield Lights to Direct the Illumination Well Below the Horizontal
Aiming lights “down” does not mean to just angle the light towards the ground. The light must be positioned so as to not allow any light to be projected above a horizontal line drawn through the lowest part of the light-producing part of the fixture. Think of that horizontal line as a line 90 degrees from a line to the ground. A better angle to cut off the illumination is around 75 degrees.
The light from a properly installed fixture should project below and out to the sides of the fixture. To facilitate this requirement to aim lights down, install lights so that the fixture is above the area to be illuminated.
Fixtures installed so they allow no light above the horizontal and no more than ten percent of their lumen output in the ten degrees immediately below the horizontal are called full cutoff (FCO). Using additional shielding to reduce the light projected in the ten degrees immediately below the horizontal to zero is even better for glare control.
An acceptable fixture that is mounted at an upward angle would change it into an “unacceptable” fixture. An acceptable fixture mounted up on a hill would require the addition of a shroud or shield to keep it from becoming unacceptable.
Shield Every Light
Light fixtures that allow no light above the horizontal and only a small amount of light near the horizontal are often recommended. In the past, these were called full cutoff light fixtures. They were considered a good option. However, we now know that light emitted near the horizontal contributes more to sky glow than any other light. A light fixture with the light source shielded so that it cannot be seen from another property, and that therefore eliminates light near the horizontal, will reduce that sky glow and eliminate light trespass.
The photo above is of a standard “shoe box” style fixture with additional shielding to stop light from being emitted near the horizontal. The light source is not seen from any other property because of the use of the shielding and the positioning of the light pole. The pole is installed at least 4 times the height of the pole away from the property line.
To improve vision, the eye must be protected from directly viewing the light source. So, even full cutoff/fully shielded lights may need additional shielding to be installed in a manner that hides the source of the light from a normal viewing point. Shielding the light concentrates it where it’s needed and usually allows you to reduce the wattage to get the same or more light where you actually need it. In fact, a wattage reduction is usually required to keep that concentrated light from producing reflective glare and an over-lighted situation.
Reduce the Amount of Light – Lumens Matter
Consider the way the human eye works when selecting the wattage, or more accurately the number of lumens, for a particular outdoor application. Using significantly less light than is the modern habit enhances night vision. Remember that a very bright light will make the unlit areas seem impossibly dark.
What you cannot tell from the “Better Lights for Better Nights” handout at the beginning of this section is the amount of light that each fixture produces. The amount of light produced is measured in lumens. Too many lumens (i.e. too bright a light) will cause light to bounce off of the surfaces it shines upon and reflect up in the sky, in the eyes of people trying to see nearby, into the habitat of nearby wildlife, etc. The light may draw in birds and insects that then won’t be able to proceed with their natural activities. So, the shape of the fixture isn’t everything. Lower the lumens (and wattage) when you switch from an unshielded fixture to a shielded fixture.
Select Lights with a Warm Color
Normally warm colored lights indicate the light produces less light in the blue wavelength. Living things need light in the blue wavelength during the morning hours but it should be reduced in the late afternoon and avoided after dark. The color temperature of light is expressed in its Kelvin rating. Old-fashioned incandescent bulbs were rated around 2700K, which is described as a warm color. Many of the bright white LEDs are rated at 5000K and upwards. This bright white light is the light that suppresses the production of melatonin in living organisms.
New light sources will usually provide the Kelvin rating. Know your application and what the color of the light does to living things. You may find it interesting to research the lighting studies led by Dr. George Brainard focused on the type of lighting used inside the International Space Station and its effects on the astronauts.
Turn Lights Off When You Are Not There or Use a Motion Sensor
Lighting an unoccupied area will normally not keep criminals away and may attract them. It’s often a waste of energy. A big plus for turning off the lights when no one is there to use them is that it allows wildlife to exist in natural darkness. As you know by now, wildlife needs natural darkness. Timers, motion detectors, and half-night photocells can help you achieve this.