SHIELDING: A fully shielded (full cut-off) light fixture has a solid barrier (cap) at the top of the fixture in which the lamp (bulb) is located. The fixture is angled so the lamp is not visible below the barrier (no light visible below the horizontal angle).
The goal of fully shielded light fixtures is to prevent the following:
1. Light trespass, which adversely affects neighboring and distant properties. Unshielded light travels much farther than people realize.
2. Glare, which can cause discomfort or temporary blindness.
3. Sky glow, which keeps all of us from enjoying the splendor of the night sky.
Many different fully-shielded light fixtures are available for all lighting situations and complement buildings with various architectural styles. The IDA website can help you find Dark Sky Friendly Lighting:
The following illustrates good and bad lighting as it relates to shielding.
All fully-shielded light fixtures provide more light on the ground since energy is no longer being wasted by lighting the sky.
More examples of good and bad lighting are pictured on the website of the International Dark Sky Association (IDA)
Landscape light fixtures that predominantly provide downlighting rather than uplighting should be chosen.
In addition to shielding, the use of timers and sensors is encouraged to minimize unnecessary lighting rather than leaving outdoor lights on all night, which is a waste of energy and an annoyance to neighbors. It should also be noted that there is no clear scientific evidence that increased outdoor lighting deters crime.
Special care must be taken in selecting fixtures for buildings on hillsides, as even meeting the “horizontal angle” requirement is not sufficient to protect owners of properties lower than the hillside site. Non-clear glass and lamps with the lowest wattage or lumens possible help prevent light trespass.