Term
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Definition
Nanometer (nm): is a unit of length in the metric system,
equal to one billionth of a meter, and as it measures tiny dimensions is used to
describe light wave lenghts. |
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Term
| Three primary properties of light |
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Definition
Intensity;
Frequency or wavelength and;
Polarization |
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Term
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Definition
Amount of light delivered by a source. Candlepower: the unit of
luminous intensity approximately equal to the horizontal light output from an
ordinary wax candle. In the SI system of measurement, this unit is the candela
(cd). |
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Term
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Definition
amount of light flowing through a unit of area. The unit of luminous flux is
the Lumen. It is equal to one candlepower of light intensity that passes across a
one foot by one foot square, from a distance of one foot. |
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Term
| Illuminance or illumination (E) |
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Definition
the density of luminous flux (F), incident on a
surface in lumens per unit area. One lumen incident on 1 sqf of area produces an
illuminance of one footcandle (fc). In SI units , lux of illuminance. |
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Term
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Definition
the luminous flux per unit of area and unit solid angle leaving a
surface, either reflected or transmitted. (Projected or apparent.) Its unit (in SI
measurements now commonly used) is the candela per square meter (cdlm2). In
th i h the inch-pound system, the unit is the footLambert, where 1 footLambert is 1
candlepower per square foot. Luminance takes into account the reflectance and
transmittance properties of materials and the directions in which they are viewed.
Thus, 100 lux striking a 1 m2 surface with 50% reflectance would result in a
luminance of 50 candelas per square meter. (In inch-pounds units , 100 fc striking a
surface with 50% reflectance would result in a luminance of 50 footlamberts .)
Luminance is sometimes called brightness, although brightness includes the
3
g , g g
physiological sensation of the adaptation of the eye, whereas luminance is the
measurable state of object luminosity. Luminance is very important because we do
not see light, we see objects that are reflecting light, and the contrast they
create. |
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Term
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Definition
the solid angular flux density in a given direction measured in
candlepower or candelas |
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Term
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Definition
| equals the angle of reflection |
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Term
Diffuse reflection results
from |
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Definition
| a uniformly rough surface |
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Term
| Combined specular and diffuse reflection |
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Definition
makes
surfaces appear to be brighter at the point where the source is shining than in the
surrounding areas. |
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