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 and those that aren’t. Fluorescent materials have absorbed light along with other radiation and proceed to give off this absorbed light. Photometers enable the measurement of the wavelength of the radiated light. For fluorescent objects, the wavelengths are usually longer, an indication of little energy being given off as compared to the much that was absorbed.
Photometers make it possible to study the intensity of a light wavelength of a material that has absorbed energy in the form of matter.
Reflection of light
Photometers enable us to study the degree to which light bounces from an object, as in the case of a mirror; or if the light is absorbed into the material. This is dependent on the nature and make-up of the object.
Scattering of light
This is where either light or sound is forced to deviate from the path it was projected. Photometers help in ascertaining the light wavelengths that have been scattered and determining to what degree it has occurred as well as its intensity.
Phosphorescence materials are similar to fluorescent ones, but the difference is seen in the amount of light emitted. Phosphorescence materials absorb the light but are very slow in radiating it out. Examples of phosphorescence are glow-in-the-dark sticks, certain types of paint and even clocks. These continue to emit light long after absorption.
Luminescence is the transmission of light but not as a result of heat. It can be due to chemical reactions or electrical energy. Most aviation tools for navigation use luminescent materials, and this makes them visible from afar off. Photometers help to distinguish which objects are luminescent and which ones are not.