The lux (symbol: lx) is the SI derived unit of illuminance or illumination. It is equal to one lumen per square metre. SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... Illuminance is the total luminous flux incident per unit area. ... In physics, specifically photometry (optics), the lumen (symbol: lm) is the SI derived unit of luminous flux. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ...

• sunlight on an average day ranges from 32 000 (32 klx) to 100 000 lux (100 klx)
• TV studios are lit at about 1 000 lux (1 klx)
• a bright office has about 400 lux of illumination
• At sunset and sunrise, ambient outdoor light is also about 400 lux (if the sky is clear).
• moonlight represents about 1 lux
• starlight measures a mere 0.000 05 lux (= 50 μlx)

Trivia: Unicode has a symbol for "lx": (㏓), but this is just a legacy code to accommodate old code pages in certain Asian languages, and it is not recommended for use in any language today. A red sunset panorama A composite image showing the terminator dividing night from day, running across Europe and Africa. ... Sunrise over the sea Sunrise, also called sunup in some American English dialects, is the time at which the first part of the Sun appears above the horizon in the east. ... In computing, Unicode provides an international standard which has the goal of providing the means to encode the text of every document people want to store on computers. ... Code page is the traditional IBM term used for a specific character encoding table: a mapping in which a sequence of bits, usually a single octet representing integer values 0 through 255, is associated with a specific character. ...

Lux versus lumen

The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.

Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area with the same number of lux requires a larger number of lumens. A compact fluorescent lamp A fluorescent lamp is a type of electric lamp that excites argon and mercury vapor to create luminescence. ...

Relationship between illuminance and power

Illuminance is not a direct measure of the energy of light, but rather of the illumination it provides as perceived by the human eye. Thus, the conversion factor varies with the wavelength composition or color temperature of light. At 555 nm, the middle of the visible spectrum, one lux is equal to 1.46 mW/m². An eye is an organ that detects light. ... The wavelength is the distance between repeating units of a wave pattern. ... White light is commonly described by its color temperature. ... A nanometre (American spelling: nanometer) is 1. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Milliwatt (SI symbol: mW) is a unit for measuring electrical power, equal to one-thousandth (10-3) of a watt. ...

SI units of light

The second (symbol s) is a unit for time, and one of seven SI base units. ... In photometry the Talbot (T) is a nonstandard unit of luminous energy. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... In physics, specifically photometry (optics), the lumen (symbol: lm) is the SI derived unit of luminous flux. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... The candela (symbol: cd, Latin for candle) is one of the seven SI base units. ... The word luminance, a synonym for luminosity, means emitting or reflecting light. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... Illuminance is the total luminous flux incident per unit area. ... Luminous efficiency is a measure of the proportion of the energy supplied to a lamp that is converted into light energy. ... The watt (symbol: W) is the SI derived unit for power. ...

Non-SI units of illuminance

• foot-candle