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
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.
Fluorescence
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.
Absorption
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
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
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.