Conversion relationship between illuminance meter brightness and illuminance unit
Luminous flux
Luminous flux: the rate of light energy emitted by a light source or the flow rate of light (Flowarte), which is the basic quantity to explain the ability of a light source to emit light, and the unit is Lumen. For example, a 100 watt (W) bulb can produce 1,750lm, while a 40W cool white fluorescent tube can produce 3,150lm of luminous flux. According to the definition, 1lm is the luminous flux emitted by a uniform point light source with luminous intensity (l) 1cd within a solid angle of 1 steradian.
light intensity
Luminous intensity (Candlepower): Luminous intensity, referred to as luminosity, refers to the luminous flux emitted from a solid angle (unit: sr) of the light source, that is, the distribution density of the luminous flux emitted by the light source or lighting fixture in the selected direction of space, The unit is candlelight (Candle or Candela, cd). A light source with a luminous intensity of 1cd can emit a luminous flux of 12.57lm. Illuminance (luminance): The density of the luminous flux received on the illuminated plane, which can be measured by the luminous flux per unit area. The luminous flux of 1lm is evenly distributed on the surface of 1 square meter (m2), that is, the illuminance of 1 lux (Lux, environmental protection technology> illuminance meter) is produced; the luminous flux of 1lm falls on the surface of 1 square foot (ft2), and its illuminance value is 1 foot candle (Footcandle, fc).
Luminance Luminance or brightness (luminance, Brightness): When the human eye sees something, it can be expressed in two ways: one is used for those with higher luminous value such as light sources or lamps, and it is directly expressed by its luminous intensity Indicates; the other is used for those who do not emit light and only reflect light, such as: indoor surfaces or general objects, expressed in brightness. Brightness is the luminous intensity emitted or reflected in a certain direction per unit area of the illuminated object, which is used to show the difference between light and shade of the illuminated object. The metric unit is Candela/m2, cd/m2 or nit (nit), the imperial unit is Footlambert (Footlambert, fl).
Reflectance or reflection factor: the brightness of a surface depends on the amount of light falling on it and the ability of the surface to reflect light; the amount and distribution of light it can reflect depends on the nature of the material surface, Expressed by the ratio of reflected light to incident light, it is called the reflectance or reflectance (%) of the surface of the material. **The reflectance of the black surface is 0, that is, no matter how much light falls on it, there is no brightness and it is all absorbed; on the contrary, the reflectance of the **white surface is 1 (reflectivity 100%, absorption rate 0% ). For the measurement of reflectance, first, place the illuminance meter on the surface of the object to read its surface illuminance value Ei (Incidentlight), and then place the illuminance value on it 5-8cm (the photosensitive part faces the surface and confirms that there is no shadow blocking), that is The reflected illuminance value Er (Reflected light) can be measured, and the quotient obtained by dividing the surface illuminance by the reflected illuminance is the reflectance of the material surface
(Illuminance meter) Conversion relationship between brightness and illuminance units Luminous flux: symbol Φ, unit lumen Lm, indicating the sum of the amount of light emitted by the luminous body per second, that is, luminous flux Light intensity: symbol I, unit candela cd, indicating that the luminous body is in a specific direction The luminous flux illuminance emitted within the unit solid angle: symbol E, unit lux Lm/m2, indicating the luminous flux brightness of the luminous body irradiated on the unit area of the illuminated object: symbol L, unit Nito cd/m2, indicating that the luminous body is in a specific direction Luminous flux and luminous efficiency per unit solid angle per unit area: the unit is lumen per watt Lm/w, indicating the ability of the electric light source to convert electrical energy into light, expressed by dividing the emitted luminous flux by the power consumption.
