1. Luminous intensity 
A: The luminous intensity (brightness, I) is defined as: point of light in the luminous intensity up a party, that is luminous body in unit time by the amount of light injection, also referred to as light, commonly used units for the candlelight (cd, candela), an international definition of a candlelight vigil for whale oil candles made from 120 per hour burning cold cell (grain) of the light emitted by a cell of cold equal to 0.0648 grams

2. What is the unit of luminous intensity (brightness)? 
A: The common unit of luminous intensity candlelight (cd, candela), the international standard candles (lcd) is defined as an ideal blackbody at the freezing point of platinum temperature (1769 ℃), the perpendicular to the blackbody (its specific surface area of 1m2) direction 60 one ten thousandth of the light, the so-called ideal black body radiation is the rate of objects equal to 1, objects can be absorbed by all the radiation energy out, so that the temperature has remained fixed uniform, international standard candles (candela) and the old standard candles (candle ) for the exchange of relations 1candela = 0.981candle

3. What is meant by flux? What is the unit? 
A: The luminous flux (φ) is defined as: point source and non-point source in unit time given by the energy, which may have a visual person (who can feel out of the radiation flux) that is known as flux. The unit of luminous flux lumens (abbreviated lm), 1 lm (lumen or lm) is defined as an international standard candles of light in the unit by three-dimensional arc angle of the flux through, the whole area of spherical 4πR2, so first-class equivalent to a prescribed luminous flux The luminous flux emitted by a candle light vigil 1/4π, or have a spherical 4π, therefore in accordance with the lumen of a cd, we can see the definition of the point radiation source will 4π lumens, that is, φ (lm) = 4πI (candlelight), it is assumed that for small △ Ω three-dimensional arc angle △ Ω in flux within the solid angle △ φ, while △ φ = △ ΩI

4. feet What is the meaning of candlelight? 
A: 1 feet away from a candlelight candlelight means of the light source (point source or non-point source) and one feet away and the surface of the orthogonal light illumination, the abbreviation for 1ftc (1 lm/ft2, lm / ft 2) , that is to receive per square foot by 1 lumen luminous flux at the time of illumination, and 1ftc = 10.76 lux

5. lux What is the meaning? 
A: per square meter received by 1 lumen luminous flux at the time of illumination

6. What is the meaning of illumination? 
A: illuminance (E) is defined as: objects illuminated unit exposed area of the luminous flux received by, or by light irradiation of the objects in unit time per unit area of the light received by the unit in meters or feet candle candlelight light (ftc) that

7. What is the relationship between the distance and Illuminance? 
A: The intensity and luminosity, is the relationship between the distance: E (illuminance) = I (light) / r2 (distance squared)