Terminology

Term

Symbol

Meaning

Luminous Flux

lm (lumens)

Luminous flux expresses the quantity of light emitted by a source

Luminous Intensity

cd (candelas)

Luminous intensity expresses the strength of light. (The quantity of light radiated within a unit solid angle).

Illuminance

lx (lux)

Illuminance, expresses the quantity (intensity) of light illuminating the unit area, and thus expresses the brightness at a given location, The illuminance is a fundamental factor in lighting and standards for it are provided by JIS regulations.

Luminance

cd/m2, nt
(candela/square meter)

Luminance expresses the brilliance of an object when viewed from a certain direction. (The strength of light emitted in a certain direction from the unit orthographic area). In contrast with illuminance which expresses the quantity of light falling upon a unit area, luminance expresses the apparent brilliance of an object when viewed from an effective direction.

Color Temperature

K (Kelvins)

The color temperature is the characteristic which determines the color of light radiated by a lamp blue-white light, and if it is low the light radiated will have a reddish tinge.

Color Rendering
Properties

 

The color rendering properties of a light source determine the way in which the color of objects illuminated by that light source appear.

Color Rendering
Index

Ra

The color rendering index indicates the fidelity of color reproduction While colors look more natural the closer this index approaches 100, color rendering indexes of 80 or greater are satisfactory for practical purposes (Based on JIS standards.)?

Rated Power Consumption Rated Lamp Wattage

W (watts)

The rated power consumption or rated lamp wattage is the lamp power consumption which is indicated on lamps and in catalogs.

Efficacy (of lamp)

lm/W
(lumen/watt)

The efficiency of a lamp equals the total luminous flux divided by the lamp's power consumption (lamp wattage).

Life

h (hours)

The life of the lamp refers to an average of measurements of the number of hours until a lamp ceases to radiate light or the period until the light radiated drops to 70% (60% for some types) of the initial value (after 100 hours on), whichever is shorter.

Average Life

h (hours)

The average life refers to the average life time of a number of lamps obtained under prescribed test conditions. This number is the life value published in catalogs.

Distribution curve of luminous intensity

 

The light dispersal curve expresses the intensity of light radiated in various directions by a light source.

Divergence

 

The divergence expresses of the concentration of light radiated from a light source. The divergence is the angle formed by the center of luminous intensity (point of maximum luminous intensity) and the points on the left and right at which luminous intensity drops to 1/2 (or 1/10) the maximum.

Beam Luminous flux

lm (lumens)

The beam luminous flux refers to the luminous flux within the beam angle.

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