science

[Tom sawyer]

what is the measuring unit of light?

[whowhatwhy]

There are 4 units:

Candela (cd)
Unit of luminous intensity of a light source in a specific direction. Also called candle.
Technically, the radiation intensity in a perpendicular direction of a surface of 1/600000 square metre of a black body at the temperature of solidification platinum under a pressure of 101,325 newtons per square metre.

Footcandle (fc or ftc)
Unit of light intensity, measured in lumens per square foot. The brightness of one candle at a distance of one foot. Approximately 10.7639 lux.

Lumen (lm)
Unit of light flow or luminous flux. The output of artificial lights can be measured in lumens.

Lux (lx)
Unit of illumination equal to one lumen per square metre. The metric equivalent of foot-candles (one lux equals 0.0929 footcandles). Also called metre-candle.

Don't ask me what one is the most commonly used though...I haven't got a clue!

[tubeway]

Also light speed is measured in metres per second (m/s) and its frequency in hertz (Hz)

[Thunderchild]

not necesarily m/s why not km ? 300.000 Km/s or 300.000.000 m/s or 300.000.000.000 mm per second

[shaun_04]

because metres per second (ms-1) is the SI unit.

[Skids]

Tubeway, Thunderchild and Shaun_04 are quoting units for the measurement of speed, which has nothing to do with light, although light does travel at a particular speed.

whowhatwhy is quoting units for the measurement of luminosity, or luminous intensity.

[tubeway]

That is because there is some ambiguity to what is actually being asked in the question. So people are trying to cover all the bases.

Thunderchild I was trying to stick to SI units - otherwise furlongs per fortnight or cubits per month would be just as relevant

[jonskinner28]

the answer is either lumens or luminous exitance. i just covered this on my course.

Jon