Luminous flux in lumens (lm) to illuminance in lux (lx) calculator and how to calculate.

Enter the luminous flux in lumens, select area unit type, enter radius in meters for spherical light source or surface area

in square meters for any light source and press the *Calculate* button to get the illuminance in lux:

## Lumens to lux calculation formula

#### Calculation with area in square feet

The illuminance *E*_{v} in lux (lx) is equal to 10.76391 times the luminous flux *Φ*_{V}
in lumens (lm) divided by the surface area *A* in square feet (ft^{2}):

*E*_{v(lx)} = 10.76391 ×* Φ*_{V(lm)} / *A*_{(ft}2_{)}

The illuminance *E*_{v} in lux (lx) is equal to 10.76391 times the luminous flux *Φ*_{V}
in lumens (lm) divided by 4 times pi times the squared sphere radius r in feet (ft):

*E*_{v(lx)} = 10.76391 ×* Φ*_{V(lm)}* *
/* *(4⋅π⋅*r*_{(ft)}^{2})

#### Calculation with area in square meters

The illuminance *E*_{v} in lux (lx) is equal to the luminous flux *Φ*_{V}
in lumens (lm) divided by the surface area *A* in square meters (m^{2}):

*E*_{v(lx)} = *Φ*_{V(lm)}* *
/* A*_{(m}2_{)}

The illuminance *E*_{v} in lux (lx) is equal to the
luminous flux *Φ*_{V}
in lumens (lm) divided by 4 times pi times the squared sphere radius r in meters (m):

*E*_{v(lx)} = *Φ*_{V(lm)}* *
/* *(4⋅π⋅*r *^{2}_{(m}2_{)})

## Lux definition

The lux (symbol: lx) is the SI derived unit of illuminance, measuring luminous flux per unit area.[1][2] It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used as both the singular and plural form.[3]

The word is derived from the Latin word for "light", lux.

Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total "amount" of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area when the luminous flux is held constant.

One lux is equal to one lumen per square metre:

1 lx = 1 lm/m^{2} = 1 cd · sr / m^{2}.

A flux of 1000 lumens, spread uniformly over an area of 1 square metre, lights up that square metre with an illuminance of 1000 lux. However, the same 1000 lumens spread out over 10 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 to the same level of lux requires a greater number of lumens.

As with other SI units, SI prefixes can be used, for example a kilolux (klx) is 1000 lux.

## Lumen definition

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time. Luminous flux differs from power (radiant flux) in that radiant flux includes all electromagnetic waves emitted, while luminous flux is weighted according to a model (a "luminosity function") of the human eye's sensitivity to various wavelengths. Lumens are related to lux in that one lux is one lumen per square metre.

If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, the total luminous flux emitted into that angle is one lumen (1 cd·1 sr = 1 lm). Alternatively, an isotropic one-candela light-source emits a total luminous flux of exactly 4π lumens. If the source were partly covered by an ideal absorbing hemisphere, that system would radiate half as much luminous flux—only 2π lumens. The luminous intensity would still be one candela in those directions that are not obscured.

The lumen can be thought of casually as a measure of the total amount of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.

The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 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. Mathematically, 1 lx = 1 lm/m^{2}.

A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens. So a lumen represents at least 1/683 watts of visible light power, depending on the spectral distribution.

Electrical power equivalents for different lamps

(source: Wikipedia)

Minimum light output (lumens) | Electrical power consumption (watts) | |||
---|---|---|---|---|

Incandescent | Compact fluorescent | LED | ||

Non-halogen | Halogen | |||

200 | 25 | 3-5 | 3 | |

450 | 40 | 29 | 9–11 | 5–8 |

800 | 60 | 13–15 | 8–12 | |

1,100 | 75 | 53 | 18–20 | 10–16 |

1,600 | 100 | 72 | 24–28 | 14–17 |

2,400 | 150 | 30–52 | 24-30 | |

3,100 | 200 | 49–75 | 32 | |

4,000 | 300 | 75–100 | 40.5 |

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