LUMINOUS FLUX:  The time rate of flow of light, measured in Lumens

Lumen:  A unit of measurement of light emitting from a lamp or light fixture.  The unit of LUMINOUS FLUX equal to one candle intensity. The lumen is the time rate of flow of light.

The quantity of luminous flux emitted within a unit solid angle (one steradian) by a point source with one candella intensity in all directions.

The unit of measure for the light energy which flows in air. The total light output from electric sources is expressed in lumens. A uniform source of one candlepower placed in a sphere emits 12.57 lumens or mean spherical candela equals to 12.57 lumens.
The unit of luminous flux; the luminous flux on a unit surface all points of which are at unit distance from a point source of one candle.

Lux:  The International Standard (SI) unit of measure for luminous flux density at a surface. One Lux equals one lumen per square meter.

Candlepower:  Luminous intensity expressed in candelas. Plots of luminous intensity, called candlepower distribution curves, are used to indicate the intensity of distribution characteristics of reflector-type lamps. A measure of intensity mathematically related to lumens. Candlepower is often used to measure the intensity of lamps that project light.

CRI (Color Rendering Index):  A rating system that indicates how colors appear under a given light source (lamp) on a scale of 100.  The higher the CRI number, the more accurately the object’s color will be represented.

Light Color:  A measurement in Kelvin (K).  Light sources with a lower Kelvin temperature 2000-3000K) exhibit more light in the red/orange/yellow range.  The higher Kelvin temperatures (>5000K) will exhibit more blue light.  Flourescent (2700K), quartz halogen (2800K) and metal halide (4000K) lamps produce an impression of “white” light.  Other examples: Candlelight-1500K, General-purpose incandescent  lamp-2100K.

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