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    What is Light Intensity (Candela)?

    Light has been very important throughout human history. When the first people discovered fire, they realized that the environment was illuminated and they understood the importance of light even at that time. While items such as candles and gas lamps have been used from past to present to illuminate the environment, today, with the development of technology, we use various technological products such as fluorescents, bulbs and LEDs to obtain light. In this week's article, we will talk about light intensity, one of the basic concepts of lighting. We wish you a good reading.

    What is Light Intensity?

    Luminous intensity is the amount of light emitted by a light source in a specified direction. In the lighting literature, luminous intensity refers to the luminous flux emitted within unit solid angle from any light source. The technological products used have different ambient illumination rates. In other words, the rate at which a simple bulb and a fluorescent lamp illuminate a room is not the same. The main reason for this is that the light intensity of light-emitting products is different. 

    What is the Light Intensity Symbol?

    The SI unit of luminous intensity is known as Candela. Briefly, the symbol of light intensity is represented as cd. Luminous intensity is also one of the seven fundamental quantities. Historically, candles were first used for light intensity measurements. This is where the name Candela, the unit of light intensity, comes from. The word candela means candle in Latin. The light intensity of a normal candle is close to 1 candela.

    How to Calculate Light Intensity?

    The formula “E=I(cos θ /d2)” is used to calculate light intensity and the result is expressed in candela (cd). As can be seen from the formula, light intensity is directly related to the distance from the light source and the angle of incidence on the surface. The formula we give is used for standard calculations. 

    Today, devices called goniophotometers are used for light intensity measurements. These devices perform measurements in candela units. Goniophotometer makes intensity measurements from different angles by rotating the light source on the vertical and horizontal axis. After measurements are made from all angles, the light intensity distribution curve is revealed. By making interpretations on this curve, the light intensity of the light source is determined.

    Luminous intensity calculation is used to measure the light intensity emitted per unit time in any direction of any light source. In other words, in the results obtained by the light intensity calculation, the light intensity in a direction determined per unit time is obtained, not the total light energy produced by the light source.

    Frequently Asked Questions

    What are light intensity measuring devices?

    While candles were used to measure light intensity in history, today a goniophotometer is used to measure light intensity.


    How is light intensity measured?

    Goniophotometer, which is a light intensity measuring instrument, is used to calculate light intensity. Light intensity calculations become much easier with a goniophotometer. 

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