|Non-cutoff optics, allow light to be emitted in all directions.
Many decorative fixtures use non-cutoff fixtures. Non-cutoff optics are
the least efficient way to put light on the ground. They are generally
effective at throwing light up into trees, and create a large amount of
light pollution and glare. These lights are not generally used as
prinicpal light sources on thoroughfares, as the glare has the tendency to
|Semi-cutoff optics, allow most of the light to be emitted below
90 degres, but some light (up to 5%) to be emitted above 90 degrees.
These types of optics are commonly used in cobra-head style
streetlighting. They are quite effective at diffusing the light over a
large, directed area on the ground. These lights still contribute some
direct uplight, although not as much as non-cutoff lights. There is still
significant glare from these fixtures, but often, they are mounted on
taller poles, which remove them from the driver's field of
|Cutoff optics have more controlled lighting than semi-cutoff.
Less than 2.5% of the light is allowed to escape the fixture above 90
degrees. Cutoff optics are now common in parking lot applications where
greater pole spacing is desired. They offer a wider spread of light than
a full-cutoff, yet they generally cannot be spaced as far apart as
semi-cutoff fixtures. These lights allow a small amount of direct uplight
to escape above the fixture.|
|Full-cutoff optics put light on the ground below the fixture
only. Full-cutoff optics do not emit light above 90 degrees. Cutoff
optics are gaining popularity around the USA, to the delight of
astronomers. These optics direct light to the ground in a defined, tight
pattern. Typically to achieve a uniform lighting job, one would have to
use more full-cutoff luminaires or increase the mounting height of those
luminaires to achieve the same result as compared with semi-cutoff or
cutoff fixtures. |
There are five different distribution patterns for streetlights, developed
by the Illuminating Engineering Society of North America (IESNA) and the
American National Standards Institute (ANSI).
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