Photometer

The photometer is an instrument or a device that measures the strength of electromagnetic radiation in the range of ultraviolet (UV) to infrared (IR). This range also includes the visible spectrum. These devices act as transducers that convert light into an electric current using special devices such as photodiodes, photomultipliers etc.

The photometer also helps measure the scattering of light, luminescence, light absorption, phosphorescence etc. While analysing the light, the device will measure the amount of light which will pass through a monochromator (or a filter) to evaluate the spectral distribution of that light. Let’s understand the different types and uses of photometers.

Uses of Photometer

There are various uses of a photometer. It is extremely useful in photography, astronomy etc. It helps us determine the following properties.

• Illuminance: Illuminance in photometry is the measure of total luminous flux (amount of perceived power of light) that is incident on a given surface per unit area. In simpler words, it tells us about the quantity of the incident light illuminating the surface.
• Absorption: Absorption is the phenomenon where a material absorbs energy in the form of matter when light hits it.
• Scattering of Light: It is the phenomenon where a light beam redirects in another direction after interacting with the particles of the medium. 
• Reflection of Light: A light ray falling on a smooth or polished surface bounces back into its medium.
• Luminescence: The property of light emission by any material in a cool state is luminescence. 

Some other applications or uses of photometers involve photon counting, UV and visible light transmission photometry, atomic absorption photometry, visible light transmission photometry etc. 

Types of Photometers

The main types of photometers are as follows:

• Visible Light Reflectance Photometer: This photometer measures reflectance as the function of the wavelength. The surface is illuminated by white light. The reflecting light passing through the monochromator is then measured. It has great application in the paint industry.
• UV-Visible Photometer: This photometer measures the absorption of light on coloured substances in a given solution. Beer’s law is the principle of such photometers. These devices can receive wavelengths ranging from 240 nm to 750 nm. The two basic types of such photometers are UV-Visible Spectrophotometer and UV-Visible Filter Photometer. UV-Visible photometers have great use in different fields of analytical chemistry and biochemistry.

• Infrared Photometer: This device helps analyse the structure of the given substance and provides the absorption rate at specific wavelengths. These photometers do not use water as the water tends to absorb infrared light very strongly. Instead of water, they use compounds in their gas phase.
• Atomic Absorption Photometer: These photometers absorb the intensity of light in a flame and analyse specific metal content. In this method, the substance for analysis is injected into the flame at a known rate and the metal within the given solution is in the form of a scattering of atoms. The discharge lamp produces monochromatic light in such photometers. Moreover, the discharge happens in the gas state with the given metal. Now, the beam will emit the light of a wavelength that will be equal to the spectral line of the metal under analysis.

Photometer vs Spectrophotometer

The basic differences between a photometer and a spectrophotometer are as follows:

Conclusion

A device that measures the strength of electromagnetic radiation within ultraviolet to infrared radiation is called the photometer. Photodiodes and photomultipliers help them convert light (photons) into electric currents. Some of the uses of photometers involve photon counting, UV and visible light transmission photometry, photography, atomic absorption photometry, visible light transmission photometry etc. There are different types of photometers, such as visible light reflectance photometers, atomic absorption photometers, infrared photometers and UV-Visible photometers.