Luminous flux

Luminosity

Luminance Chamber

photometry radiometry units

Luminous flux is a measure of the perceived power of light. It represents the quantity of light emitted by a source or received by a surface, based on the wavelengths to which the human eye is sensitive. The unit of luminous flux in the International System of Units (SI) is the lumen (lm). Luminous flux is an integral part of understanding how light works in the fields of photometry, lighting design, and vision science.

Definition

Luminous flux, in simple terms, quantifies the total amount of visible light emitted by a source or incident on a surface. Unlike radiant flux, which measures all electromagnetic radiation emitted by a source, luminous flux is weighted according to the V-Lambda curve, which represents the average sensitivity of the human eye to different wavelengths of light. The V-Lambda curve peaks at 555 nm, corresponding to green light, where the eye is most sensitive, and diminishes towards the red and blue ends of the visible spectrum.

Measurement

The SI unit of luminous flux is the lumen. One lumen is defined as the luminous flux from a light source that emits one candela of luminous intensity uniformly across a solid angle of one steradian. The formula to calculate luminous flux (\(\Phi_v\)) is given by:

\[ \Phi_v = I_v \times \Omega \]

where \(I_v\) is the luminous intensity in candelas and \(\Omega\) is the solid angle in steradians through which the light is emitted.

Applications

Luminous flux is a critical parameter in many applications, including:

• Lighting design: It helps in determining how much light is required to adequately illuminate a space for various activities.
• Energy efficiency: Comparing the luminous flux of light sources to their power consumption (in watts) gives a measure of their efficiency in terms of lumens per watt (lm/W).
• Photometry: It is a fundamental quantity in photometry, used to characterize and compare light sources.

See also

• Illuminance
• Luminous intensity
• Luminous efficacy
• Color rendering index

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