When defining the Initial Intensity of a light source, define the parameters as follows.
| Parameter | Description |
|---|---|
| Wattage | A measurement of the electrical power consumed by a light source. Tip: When adjusting Wattage, it is also important to consider Efficacy. If you change Wattage alone, you may make the light source unintentionally bright. Luminosity is defined as Wattage (W) times Efficacy (W/lm). Luminous Efficacy for a 100 W tungsten incandescent (110 V) is 175, while a 32 W fluorescent tube (T8) is 60.
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| Efficacy | The amount of light (luminous flux, measured in lumens) produced by a light source as a ratio of the amount of energy consumed to produce it (measured in watts). |
| Luminous Flux | The quantity of light energy per unit of time arriving, leaving, or going through a surface. The lumen (lm) is the unit of luminous flux in both the International System (SI) of units and in the American System (AS) of units. If you think of light as particles (photons) moving through space, then the luminous flux of a light beam arriving at a surface is proportional to the number of particles hitting the surface during a time interval of 1 second. Tip: In general, Luminous Flux provides more accurate lighting in rendered images than Wattage and Efficacy.
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| Luminous Intensity | The light energy per unit of time emitted by a point source in a particular direction. Luminous intensity is used to describe the directional distribution of a light source, that is, to specify how the luminous intensity of a light source varies as a function of the outgoing direction. The Candela (cd) is the unit of luminous intensity. |
| Illuminance | The luminous flux incident on a surface of unit area. Illuminance measures how much energy has fallen on a surface. This quantity is useful for describing the level of illumination incident on a surface without making the measurement dependent on the size of the surface itself. The lux (lx) is the International System (SI) unit of illuminance. The American System (AS) unit for illuminance is the footcandle (fc), equivalent to 1 lumen per square foot. |
| At a distance of | Illuminance is a function of the distance from the light source. Specify the distance at which the illuminance is measured. |