What Is A Photometer And What Is It used for?

Photometry is the science that studying light, concerning its brightness. Photometry used to be done using the human eye until electric light sensitive tools like the photometer was invented. So what is a photometer and what is it used for? A photometer is a device used to measure diverse aspects of the intensity of light. The instrument is used in photography, soil testing, and the water industry. It is used to compare light transmitted from two sources, when the specific characteristics from one source are known and are standard and the other unknown. The photometer gives an accurate comparison of light from different sources. An example of how a photometer works is by putting a piece of paper with an oil stain in the middle of it that makes that part of the paper transparent. When you observe that you cannot make out the oil spot from either side, it is said that the illumination or light intensity from the sides is proportional.


Types of Photometers

There are five types of photometers mainly used in photography as explained below.


Color photometers

Color photometers measure the amount of light falling on an object along with the intensity of color coming from it. Such photometers are used to balance out the saturation of color and are particularly useful when it comes to photography.


Hand-held photometers

These are used to concentrate on light readings in some locations of a photograph.


Built-in photometers

These are photometers that are integrated into the camera. The practice came about when the importance of a photometer in picture taking was discovered.


Spot photometers

Here, light readings are gotten from different areas of the subject being photographed, and then the photographer uses these readings so that he/she may know how to set the exposure of the camera for the studied areas.


Incident-light photometers

These photometers use an incident-light meter that measures the amount of light falling on the subject. It is the most accurate of the five photometers.


In around 1861, three different types of photometers were adopted for use then, and they are as follows;

Ritchie’s photometer

The photometer was used to determine uniform illumination of light on different surfaces.


Rumford’s photometer

Rumford’s photometer works on the notion that the brighter a light source is, the thicker the shadow it cast.


Method of extinction of shadows

Here, the photometer works by removing shadows, as the process implies. If a light source casts the shadow on an opaque object onto a screen, if a second source is introduced at a certain distance, it will eradicate the shadow.



When it comes to the water industry, the following are the different types of photometers required.

  • Photometers that are used in pisciculture that is, fish farming. They ensure that the right amount of light is available in the water for the fish to survive as well as thrive.


  • Photometers that ascertain the level of oxygen in water along with the ph of the water. The photometer also determines if there is the presence of any phosphates or other minerals.


  • Photometers that are used in pools and bathrooms for control of the amounts of light that can be absorbed in the materials.


  • Photometers that establish the oxygen demand in water bodies needed for different purposes.

Uses of Photometers

Just to reiterate, photometers are used to measure light intensity. Photometers do so in the following ways.



Illuminance is the measure of the degree to which light illuminates a surface, and the wavelength is weighed luminosity function to compare it with the perception of the brightness witnessed by the eye. The human eye is used here because it was the first object that was used to determine the intensity and it can differentiate a broad range of light.



Photometers help us to distinguish between materials that are fluorescent