Friday, March 22

Light Measurement

There are many different units for Light Measurements. Let’s first discuss some of them.

1. Candela (cd)- It is the unit of Lumen Measurement of a light source in a specific direction, also called as candle. This intensity is perpendicular to the direction of the surface of a black body.
2. Foot candle (fc or ftc)- It is a unit of intensity which used to measure in lumens per square foot.
3. Lux (lx)-  It is the unit of illumination which equals to one lumen/ square metre.
4. End Foot candle- This unit is a measurement which is based on the focused beam only. It is a focal beam measurement from point A to point B at one-foot distance.
5. End Lumens- This measurement is based on a spot of light.

6. Luminance- Also called as Luminous Flux which is the quantity of light leaves the lamp and measured in lumens (lm).
7. Luminous (Light Level): It is the amount of light measured on the work plane in the lighted space. Remember a work plane is an imaginary horizontal, tilted or vertical line where the tasks in the space are performed.
8. Beam Lumens- It is the total flux in that region of space where the intensity is more than 50 percent of the maximum intensity.
9. Lux- It is a metric unit of measure for illuminance of a surface. One lux = one lumen/ square meter= 0.0929 footcandles.
10. Light Level- It is the measurement of intensity on a plane at a specific location known as illuminance which is measured in footcandles.
11. Efficiency—the measure of the luminous efficiency of a radiant flux which is expressed in lumens/ watt is equals to efficiency.
12. Watt- It is a measurement of electrical power which does not relate to the output level and defines as the rate of energy consumption by an electrical device in operating stage. Watts= Volts x Amps x Power Factor (PF)

The wavelength is a length of a function period which shows the distance between any two points with the same phase and measured in meter light.  Let’s discuss; ‘How to Measure Wavelength of Light’? It can calculate either from the energy or frequency by using the speed and Planck constants. Remember the energy is typically expressed in electron volt (eV) units and the frequency is expressed in Hertz where one Hz equals 1/sec. Therefore the relation between velocity, frequency and wavelength can be written as follows;

Velocity of Light = (wavelength) x (frequency)(meters) x (cycles per second or Hertz)
= (3 x 108 m/sec)

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