# Light Measurement

Thereare many different units for Light Measurements. Let’s firstdiscuss some of them.

1. Candela(cd)- It is the unit of Lumen Measurement of a light source in aspecific direction, also called as candle.This intensity is perpendicular to the direction of the surface of ablack body.

2. Footcandle(fc or ftc)- It is a unit of intensity which used to measure inlumens per square foot.

3. Lux(lx)- It is the unit of illumination which equals to one lumen/square metre.

4. EndFootcandle- This unit is a measurement which is based on the focusedbeam only. It is a focal beam measurement from point A to point B atone-foot distance.

5. EndLumens- This measurement is based on a spot of light.

6. Luminance-Also called as Luminous Flux which is the quantity of light leavesthe lamp and measured in lumens (lm).

7. Luminous(Light Level): It is the amount of light measured on the work planein the lighted space. Remember a work plane is an imaginaryhorizontal, tilted or vertical line where the tasks in the space areperformed.

8. BeamLumens- It is the total flux in that region of space where theintensity 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. LightLevel- It is the measurement of intensity on a plane at a specificlocation known as illuminance which is measured in footcandles.

11. Efficiency—themeasure of the luminous efficiency of a radiant flux which isexpressed in lumens/ watt is equals to efficiency.

12. Watt-It is a measurement of electrical power which does not relate to theoutput level and defines as the rate of energy consumption by anelectrical device in operating stage. Watts="Volts" x Amps x PowerFactor (PF)

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

Velocityof Light = (wavelength) x (frequency)(meters) x (cycles per second orHertz)

=(3 x 108m/sec)

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