Ch. 10 & 11

the science that measures light. Light is really visible energy.

Light emitted in a specific direction by a source (luminance intensity) measured in candelas (cd)

light emitted in all directions by a source (luminous flux) measured in lumens

density of light at any given point on a surface. Measured in footcandles. (fc)

accepted term for light that is reflected from a surfac in a given direction

total quantity of light emitted, reflected, or transmitted in all directions from a surface. measured in lumens per square foot (lm/ft2)

flow of electricity

potential of flow 120/240 volt

rate of flow, volt per second

path that current flows

material that allows flow

• rate of change.
• Volts x amp = watts

amount of electrical power consumed over a period of time

• the interval that flow changes direction.
• measured in Hertz (Hz)

the flow of electricity in a circuit when it is open ("off") and it allows unimpeded flow when closed ("on")

switch is connected at any point between the luminiare and the power supply

is able to direct the current to two paths at once.

controls an electrical load from two locations; this allows the circuit to use one of two alternate paths to complete itself

• 1) varying the voltage
• 2) varying the length of time that the current flows during each alternating current cycle

Dimming incandescent sources

The source is operated at less than its designed voltage because the temperature of the filament is reduced. Even though the lamps are less efficient at producing light, much energy is still being saved.

The use of special dimming ballasts, which replace the standard ballast and must be compatible with the dimming control device.