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METHODS OF CONTROLLING LIGHT A luminaire,
often called a light fixture, is a complete lighting
unit that produces and distributes light to fulfill
the design goals for the lighted space.
The primary methods of controlling light from a bare
light source via a light fixture are reflection, transmission
and refraction. Other methods include polarization,
interference and absorption. In this article, we will
discuss the first three.
Reflection
Reflection, the most common form of controlling
light, occurs when light rays impact and are
then reflected from a surface. The types of
reflection include:
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·
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Specular - Specular reflection is
when light is reflected from a highly polished
surface such as smooth polished metal, producing
a consistent angle. |
· |
Diffuse - Diffuse reflection is when light is
reflected from a rough surface, producing a variety
of angles depending on how the light impacts each
tiny part of the rough surface. Diffuse reflection
is typically used to minimize glare, hot spots
and shadows. |
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Spread - Spread reflection is when light is
reflected into a cone of light rays from surfaces
such as corrugated or etched metal, plastic or
glass. |
· |
Selective - Selective reflection is when
a colored surface is used so that only certain
color wavelengths or reflected as opposed to
absorbed or transmitted.
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Transmission
Transmission occurs when light rays are passed
through a material. The types of transmission
include:
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Direct - Direct transmission is
when light rays go through the material with no
change to their direction or color. Example: Clear
plate glass.. |
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Diffuse - Diffuse transmission is when light
rays are widely spread, useful when we want to
obscure the light source and produce a uniform
appearance of light on the transmitting surface.
Example: Inside-frosted glass. |
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Spread - Spread transmission is when the maximum
intensity of light rays passed through with little
change in direction, producing a glow on the transmitting
surface and a sense of sparkle. |
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Selective - Selective transmission is when
selected color wavelengths are allowed to pass
through the material. Example: Colored glass.
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Refraction
Refraction, used in prismatic lenses in fluorescent
fixtures, floodlighting and streetlighting,
occurs when light rays pass through one material
and into another at a different intensity.
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