Knowledge of Light



·illumination
the process of seeing is as the light illuminate the object with the environment in the scene.

illuminative environment

the physiological and psychological effects relate to the light.


·luminous flux

indicates all the radiated power emitted by a light source in all directions, evaluated at spectral at spectral eye sensitivity.

unit: lumen [lm]


·luminous intensity (lux)
a light source generally emits it luminous flux in different directions. luminous intensity is the luminous flux emitted through unit solid angle (1 steradian) in a particular direction.
unit: candela (cd)

·illuminance (e)
illuminance is the total luminous flux incident on a surface, per unit area.
unit: lm/㎡

·luminance (l)
luminance is a photometric measure of the density of luminous intensity in a given direction. it describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle.
unit: candela per square meter = (cd/㎡)

·color temperature
temperature of the black body that emits radiation of the same chromaticity as the radiation considered.
unit: kelvin, (k).


·color rendering index

color rendering index is the measure of the degree to which the psycho-physical colors of objects illuminated by the source conform to those of the same objects illuminated by a reference illuminant for specified conditions.


·dazzling light
the conditions of the unsuitable luminance distribution or the scope or the strong contrast gradient causes discomfort or weaken the ability of distinguishing.

·uncomfortable dazzling light
the light causes the uncomfortable sense, not reducing the visibility of the object surely.

·disabled dazzling light
the light reduces the visibility of object, not causing uncomfortable sense surely.
the dazzling light is caused by reflection, special the reflection occurring on the same or contiguous directions of the observing object.

·light curtain reflection
it appears on the object the mirror surface, not distinguishing the object partially or completely.

·bright vision
the object provides human’s visual information---5 factors 1. color 2.luminace 3. contrast 4. size 5. migration:
the human obtains the visual information. it needs to be in the bright vision, same as the suitable degree of illumination; the vision is clear, rich in level, and causing the color senses. therefore, under the appropriate degree of illumination, the wyes can distinguish the object easily, such as the clearly, the rich level, and plentifully color easily. the eyes are used for a long time; the moderate degree of illumination is able to alleviate the eye weariness, protecting vision.

·illumination appliance
the appliance that can distribute penetrate or transforms the light, shining out from one or many light sources according to the design, including all parts used to strut, fix and protect the light source, as well as essential electric circuit auxiliary appliance and power source equipment without light source itself.

·general illumination
one location basic balancing illumination, not providing the special spot lighting.

·spot lighting
the illumination for special visual purpose, as assistant for ordinary illumination and separate controlled.

·direct lighting
with the aid of the characteristic of light-intensity distribution in the lamps and lanterns, radiates the 90%-100% luminous flux on the working surface directly.

·indirect lighting
with the aid of characteristic of light-intensity distribution in lamps and lanterns, 0%-10% luminous flux direct radiates on working surface directly, and through the reflection.
·the illumination uniformity to the surface ( in an assigned plane)
the ratio is measured by the smallest degree of luminance intensity.

·luminaries efficiency
it is the ratio between the luminous flux emitted by the luminaries to the luminous flux of the lamp (or lamps) installed in the luminaries.

·luminous efficacy
quotient of the luminous flux emitted power consumed.
unit: lumen per watt [lm/w]

·life of light source

the duration of a lamp’s working hours, or the total working hours until to be considered out of efficiency according to a certain standard.