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# Ten FAQs about LED lights

## 1. What is the luminous intensity (luminosity) of LED lights?

Answer: The luminous intensity (luminosity, I) is defined as: the luminous intensity of a point light source in a certain direction, that is, the amount of light emitted by the luminous body in a unit time, also referred to as luminosity, the common unit is candlelight (cd, candela), An international candlelight is defined as the luminosity of a candle made of whale oil burning 120 grains per hour, and one grain is equal to 0.0648 grams.

## 2. What is the unit of luminous intensity (luminosity)?

Answer: The commonly used unit of luminous intensity is candlelight (cd, candela), the international standard candlelight (lcd) is defined as the ideal blackbody at the platinum freezing point temperature (1769 ℃), perpendicular to the blackbody (its surface area is 1m2) in the direction of 600,000 points One of the luminosities, the so-called ideal blackbody means that the emissivity of the object is equal to 1, the energy absorbed by the object can be radiated out completely, so that the temperature has always been uniformly fixed. The international standard candle (candela) and the old standard candle (candle) are interchanged The relationship is 1candela = 0.981candle.

## 3. What is luminous flux? What is the unit of luminous flux?

Answer: The definition of luminous flux (φ) is: the energy emitted by a point light source or a non-point light source in a unit of time, which can produce the visual person (the radiant flux that humans can feel) is called the luminous flux. The unit of luminous flux is lumens (abbreviated as lm). 1 lumens (lumen or lm) is defined as the luminous flux of an international standard candle light source passing through the unit solid arc angle. Since the entire spherical area is 4πR2, the first-class bright light flux is equal to one candle. The luminous flux emitted is 1 / 4π, or the spherical surface has 4π, so according to the definition of lumens, a cd point light source will radiate 4π lumens, that is, φ (lumens) = 4πI (candle light), assuming that △ Ω is a small solid arc Angle, the luminous flux △ φ in the △ Ω solid angle, then △ φ = △ ΩI.

## 4. What is the meaning of 1 foot candlelight?

Answer: 1 foot candle light refers to the illuminance on a surface that is one foot away from a candle light source (point light source or non-point light source) and orthogonal to the light. It is abbreviated as 1ftc (1lm / ft2, lumen / ft2), that is, each The luminous flux received in a square foot is the illuminance at 1 lumen, and 1ftc = 10.76lux.

## 5. What is the meaning of 1 meter candlelight?

Answer: 1 meter candle light refers to the illuminance on a surface that is one meter away from a candle light source (point light source or non-point light source) and is orthogonal to the light. The luminous flux received inside is the illuminance at 1 lumen (lumens / m2).

## 6. What is the meaning of 1 lux?

Answer: The illuminance when the luminous flux received per square meter is 1 lumen

## 7. What is the meaning of illuminance?

Answer: The illuminance (E) is defined as: the luminous flux received by the illuminated object per unit illuminated area, or the luminosity received by the object illuminated by light per unit area per unit time, the unit is meter candlelight or foot candlelight ( ftc) said.

## 8. What is the relationship between illuminance, luminosity and distance?

Answer: The relationship between illuminance, luminosity and distance is: E (illuminance) = I (luminosity) / r2 (distance squared).

## 9. What factors are related to the illuminance of the subject?

Answer: The illuminance of the subject is related to the luminous intensity of the light source and the distance between the subject and the light source, but not to the color, surface properties and surface area of the subject.

## 10. What is the meaning of light effect (lumen / watt, lm / w)?

Answer: The ratio of the total luminous flux emitted by the light source to the electric power consumed by the light source (Watts) is called the light effect of the light source

## 11. What is color temperature?

Answer: When the color emitted by the light source is the same as the color radiated by the black body at a certain temperature, the temperature of the black body is the color temperature.

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