The illuminance is 1 lux if a luminous flux of 1 lumen falls uniformly on an area of 1 m².Īnother formula for calculating illuminance at greater distances is as follows: Lux = luminous intensity / radius or distance squared Illuminance is calculated with the following formula: Lux = luminous flux / area. The value lux is purely a receiver quantity. Lux indicates how much luminous flux (lumen) of a light source arrives per unit area of a receiver surface. It is a measure of the brightness with which an area is illuminated. Lux provides information about the illuminance. From this, conclusions can be drawn about the luminous intensity.Ī standard candle, for example, emits a luminous intensity of 1 cd, i.e., it emits about 12 lumens (lm) in all directions. This creates a luminous intensity distribution curve. If the calculation according to the above formulae is not possible for the lamp, a light measurement can be carried out with an integrating sphere and a spectrometer. If the solid angle is not known, but only the beam angle, this can be determined with a conversion formula: Luminous intensity = luminous flux / solid angle. The units of luminous flux are lumens, for the solid angle it is steradians.

The value of the luminous- or light intensity is given in candela. To determine the luminous intensity of a lamp, you need the luminous flux and the beam angle or solid angle. The luminous intensity of the lamp with the smaller beam angle is higher than that of the lamp with the wider beam angle. The diagram shows two lamps with the same luminous flux (lumen) but different beam angles. The more focused the light is emitted, the more intense it is. The luminous intensity or its candela value indicates how intensively the light is emitted. The beam angle indicates the angle at which the light is emitted by the lamp. Lamps with the same luminous flux can have completely different luminous intensities due to their beam angle.

Luminous intensity is an important value for comparing different lamps. As an example, the luminous intensity of a candle is approximately one candela. What is the metric unit used for measuring luminous intensity? Candela (cd) is the metric unit of luminous intensity. The luminous intensity therefore indicates how concentrated the light is or what density the emitted light has. It relates the light flux to the beam angle of a light source. Light intensity is one of the photometric quantities. Since the radiation behavior of an optical signaling device is not only determined by the light source but also by the design of the domes, the luminous intensity is best suited to characterize the signaling effect of optical signaling devices.

The luminous intensity is a photometric value that describes the radiation of light emitted in a certain direction. What is light intensity (candela definition)? Exemplary lumen values: Fluorescent tube (48 Watt)Įxamples of the luminous efficacy of different lamps: Incadescent lamps The higher the value, the more efficient a light source is. It is the ratio of lumens to power or watts, so it is measured in lumen per watt (lm/W) in the International System of Units (SI). The luminous efficacy is a measure that indicates how efficient a light source is. Compact fluorescent lamp/energy-saving lamp: with 15 W electrical power: luminous flux Φ = 900 lm Incandescent lamp with 15 W electrical power: luminous flux Φ = 90 lm Two examples of typical luminous flux values: Short wavelengths are termed ultraviolet and longer waves are termed infrared. How bright and colourful the human eye can perceive a light depends on the wavelength of the radiation and the intensity with which the radiation hits the retina. When visible light is emitted, this is also called luminescence. Light is created when energy is converted.

They travel in waves and transmit energy impulses. Light consists of photons, also called light particles. The total luminous flux emitted by a light source over a certain period of time. The ratio of emitted luminous flux to required electrical power. The measure for the impression of brightness of a surface, perceived by the human eye. The measure for the light that arrives at a receiver surface. Gives information about how much light is radiated in a certain direction. The measure for the total amount of light emitted by a light source. The following table provides an overview of the most important photometric quantities and units: Photometrische Größe In light measurement, a distinction is made between various photometric quantities by which the unit of light intensity can be evaluated. Important photometric quantities and units

Equations for light intensity