The Light Meter The Light Meter An Introduction to Photometry An Introduction to Photometry

What is Photometry What is Photometry Photometry focuses on assigning numerical Photometry focuses on assigning numerical values to light energy emitted from wavelengths values to light energy emitted from wavelengths between 400nm and 700nm. This is the visible between 400nm and 700nm. This is the visible light portion. light portion.

A subject called Radiometry focuses of most of A subject called Radiometry focuses of most of the EM spectrum (400nm to 1000nm). the EM spectrum (400nm to 1000nm).

This light meter from Quantum Instruments is This light meter from Quantum Instruments is just for Photometry use. just for Photometry use.

Think of this value as what Amps or Volts is to Think of this value as what Amps or Volts is to electricity. electricity.

The Light MeterThe Light Meter

All light meters holds a plain silicon detector All light meters holds a plain silicon detector inside of it (Silicon Photo Diode) which can be inside of it (Silicon Photo Diode) which can be used for radiometry or photometry. This meter used for radiometry or photometry. This meter can only be used for photometry however due to can only be used for photometry however due to the green filter which only allows wavelengths the green filter which only allows wavelengths from 400nm to 700nm to arrive to the detector. from 400nm to 700nm to arrive to the detector. This filter simulates the energy or light our eyes This filter simulates the energy or light our eyes can see and assigns numerical values for them.can see and assigns numerical values for them.

It is called a light meter, Photo Meter, and It is called a light meter, Photo Meter, and sometimes Photometersometimes Photometer

What Exactly Does it What Exactly Does it Measure?Measure?

This specific light meter can measure two This specific light meter can measure two variables. variables.

One is the Illuminace value which is measured One is the Illuminace value which is measured in Lux. This white filter must be placed over in Lux. This white filter must be placed over the green filter. A lux is equal to [lm/m^2].the green filter. A lux is equal to [lm/m^2].

The other variable is the Luminance value The other variable is the Luminance value which is measured in [cd/m^2]. To measure which is measured in [cd/m^2]. To measure this the aperture must be placed over the this the aperture must be placed over the green filter. green filter.

IlluminanceIlluminance

Illuminance measures the intensity or power of Illuminance measures the intensity or power of the light over a surface, per unit area. [lm/m^2] the light over a surface, per unit area. [lm/m^2] or [Lux]or [Lux]

This White filter is used to collect light from all This White filter is used to collect light from all angles and get rid of the dimensional aspects of angles and get rid of the dimensional aspects of where the light is coming from. where the light is coming from.

To capture the illuminance value it must To capture the illuminance value it must integrate all the light into one source. integrate all the light into one source.

LuminanceLuminance

Luminance is the measure of the intensity of the Luminance is the measure of the intensity of the light per unit area of light traveling in a certain light per unit area of light traveling in a certain direction. direction.

This direction of the light is the difference This direction of the light is the difference between Illuminance and Luminancebetween Illuminance and Luminance

The aperture is used over the green filter to The aperture is used over the green filter to measure Luminance because it only allows light measure Luminance because it only allows light in from a fixed, known angle. in from a fixed, known angle.

Luminance is measured in [cd/m^2]Luminance is measured in [cd/m^2]

How do you use it?How do you use it? The Side which Says Photometer The Side which Says Photometer should be facing up when held. should be facing up when held.

The button on the right is called The button on the right is called Measure control. You hold this button Measure control. You hold this button down to take a measurement.down to take a measurement.

If the Display shows three dashed If the Display shows three dashed lines, the light intensity is out of range. lines, the light intensity is out of range.

If the light intensity is out of range you If the light intensity is out of range you hold on Range button (on the left hold on Range button (on the left side). This will change the decimal side). This will change the decimal places. places.

Photometers need to be calibrated to Photometers need to be calibrated to work correctly.work correctly.