Common Electrical Terms, Abbreviations and Definitions
lumen (lm)
Practical Definition: This is a measurement of how bright a light source is rated. Really not a good
practical measurement. An example is when you purchase a 100-watt light bulb. Watt is the power
consumed, not a measurement of light, but we all know that a 100-watt light bulb is pretty bright.
Used to compare two light sources to one another. See Lux definition below.
Technical Definition: The lumen (symbolized lm) is the International Unit of luminous flux. A unit of
luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one
candela (see definition below) intensity.
lux (lx)
Practical Definition: Lux is the amount of light you actually see. One lux is equal to one lumen per
square meter. It is the amount of light cast on a surface. This is the most practical measurement of
light. See the chart below for examples:
Illuminance
0.00005 lux
0.0001 lux
0.001 lux
0.01 lux
0.25 lux
1 lux
10 lux
50 lux
80 lux
400 lux
400 lux
1000 lux
32000 lux
100000 lux
Abbreviation
50 µlx
100 µlx
1 mlx
10 mlx
250 mlx
1 lx
10 lx
50 lx
80 lx
400 lx
400 lx
1 klx
32 klx
100 klx
Pronunciation
50 micro-lux
100 micro-lux
1 milli-lux
10 milli-lux
250 milli-lux
1 lux
10 lux
50 lux
80 lux
400 lux
400 lux
1 kilo-lux
32 kilo-lux
100 kilo-lux
Example
Starlight
Moonless overcast night sky
Moonless clear night sky
Quarter Moon
Full Moon on a clear night
Moonlight at high altitude at tropical latitudes
Candle at a distance of 1 ft
Family living room
Hallway/Toilet
A brightly lit office
Sunrise or sunset on a clear day
Typical TV studio lighting
Sunlight on an average day (min.)
Sunlight on an average day (max.)
Engineering Definition: The lux (symbol: lx) is the unit of illuminance and luminous emittance. It is
used in photometry as a measure of the intensity of light, with wavelengths weighted according to
the luminosity function, a standardized model of human brightness perception. It is used as a
measure of the intensity of light. In English, "lux" is used in both singular and plural. 1 lux = 1
lumen/sq. meter.
foot-candle (fc)
Practical Definition: In practical applications, as when measuring room illumination, it is very
difficult to measure illuminance more accurately than ±10%, and for many purposes it is quite
sufficient to think of one foot-candle as about ten lux. Therefore, it is commonplace to simply state
1 fc = 10 lux.
Technical Definition: One foot-candle ≈ 10.764 lux. The foot-candle (or lumen per square foot) is a
non-SI unit of illuminance. It is obsolete but it is still in fairly common use in the United States,
particularly in construction-related engineering and in building codes. Because lux and foot-candles
are different units of the same quantity, it is perfectly valid to convert foot-candles to lux and vice
versa.
Common Electrical Terms, Abbreviations and Definitions…pg 2
The name "foot-candle" conveys "the illuminance cast on a surface by a one-candela source one
foot away.” As natural as this sounds, this style of name is now frowned upon, because the
dimensional formula for the unit is not foot · candela, but lumen/sq ft. Some sources do however
note that the "lux" can be thought of as a "meter-candle" (i.e. the illuminance cast on a surface by a
one-candela source one meter away). A source that is farther away provides less illumination than
one that is close, so one lux is less illuminance than one foot-candle. Since illuminance follows the
inverse-square law, and since one foot = 0.3048 m, one lux = 0.30482 foot-candle ≈ 1/10.764 footcandle.
ampere (amp or A)
Practical Definition: The ampere, in practice often shortened to amp, is a unit of electric current, or
amount of electric charge per second.
Technical Definition: The base unit of electric current in the International System of Units that is
equal to a constant current which when maintained in two straight parallel conductors of infinite
length and negligible circular sections one meter apart in a vacuum produces between the
conductors a force equal to 2 × 10−7 newton per meter of length.
ampere–hour (Amp-Hours or Ah)
Practical Definition: A unit of measure to describe how long a battery will run. For example, a 12
Ah battery will run for 12 hours with a 1 amp load on it, or 6 hours with a 2 amp load on it, or 3
hours with a 4 amp load on it, and so on.
Technical Definition: A unit quantity of electricity equal to the quantity carried past any point of a
circuit in one hour by a steady current of one ampere.
Light Emitting Diode (LED)
Practical Definition: A very small light source used in electronics.
Technical Definition: A semiconductor diode that emits light when a voltage is applied to it and that
is used especially in electronic devices (as for an indicator light).
watt (W)
Practical Definition: A unit of power, often incorrectly associated with light output.
1 Watt = 1 Volt x 1 Amp
Technical Definition: The watt (symbol: W) is the SI derived unit of power, equal to one joule of
energy per second. That is, if 1 volt of potential difference is applied to a resistive load, and a
current of 1 ampere flows, then 1 watt of power is dissipated.
Common Electrical Terms, Abbreviations and Definitions…pg 3
volt (V)
Practical Definition: Volt is used to quantify the electrical potential of an electrical source. See list
below for common examples:
Nominal voltages of familiar sources:
• Nerve cell action potential: around 75 mV
• Single-cell, rechargeable NiMH or NiCd battery: 1.2 V
• Mercury battery: 1.355 V
• Single-cell, non-rechargeable alkaline battery (e.g. AAA, AA, C and D cells): 1.5 V
• Lithium polymer rechargeable battery: 3.75 V
• Automobile electrical system: "12 V", about 11.8 V discharged, 12.8 V charged, and 13.814.4 V while charging (vehicle running).
• Household mains electricity: 120 V in North America
• Rapid transit third rail: 600 to 750 V
• High speed train overhead power lines: 25 kV (kilo-volt)
• High voltage electric power transmission lines: 110 kV (kilo-volt)
• Lightning: Varies greatly, often around 100 MV (mega-volt)
Technical Definition: The unit of electrical potential difference and electromotive force equal to the
difference of potential between two points in a conducting wire carrying a constant current of one
ampere when the power dissipated between these two points is equal to one watt and equivalent to
the potential difference across a resistance of one ohm when one ampere is flowing through it
Rated Power: the maximum amount of wattage (W) the solar panel is rated for
Peak Power: the maximum amount of power in watts (W) the solar panel will produce
Peak Power Voltage: the maximum amount of voltage (V) or power the solar panel will produce
Peak Power Current: the maximum amount of current in amps (A) that the solar panel will produce
Open Circuit Voltage: a short spike in voltage (V) that is not sustained over a period of time
Short Circuit Current: a short spike in amps (A) that is not sustained over a period of time
UV: (Ultra Violet) beyond the visible spectrum at its violet end -- used of radiation having a
wavelength shorter than wavelengths of visible light and longer than those of X-rays