What is Photometry?
Photometry is defined as the science of the measurement of the visible range light, in terms of its brightness to the human eye. Photometry is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power. Photometry only relates to the visible range of wavelength (light).
What we call “light” is simply the radiation within this visible range. Hence, light has a wavelength range which human beings can observe. All radiation has its own energy and light has the energy to stimulate eyes. The human eye can detect radiations that have a wavelength in the range of 370 nm to 780 nm.
The human eye cannot stimulate the energy of radiation whose wavelength is more or less than the range of light. The radiation which has wavelength more than light is known as infrared radiation and the radiation which has a wavelength less than light is known as ultra-violet radiation. Photometry does not include infrared or ultraviolet radiation.
What is Fiber Photometry?
Fiber photometry is related to neuroscience. It is a technique to record neural dynamics and used to correlate the behavior of animals with neural activity.
It is used to monitor signals from the fluorescent indicator in generically defined neural in behaving animals. It is an optical recording technique that uses the light detector, light source, and an optical fiber implanted in the animal brain.
Animal brain to deliver excitation light to neurons with a fluorescent indicator and collect overall induced fluorescence.
Fiber Photometry Calcium Imaging
The genetically encoded calcium indicators are used in fiber photometry. GCaMP is a short form of Genetically Encoded Calcium Indicator.
It is used to record the neural activity of neurons through an optical fiber in animals. This allows understanding the temporally specific signaling that encodes information about features of the environment attract and that predicts their occurrence.
What is Flame Photometry?
Flame photometry is used for inorganic chemical analysis to determine the concentration of metal ions. And it is used for metals like sodium, potassium, calcium, and lithium.
The species of group-1 (alkali metal) and group-2 (alkaline earth metal) are separated. For this purpose, the thermal energy is used. And thermal energy is produced by the Flame.
When we apply thermal energy, some atoms are excited to a higher energy level. But atoms are not stable at this level.
Unstable atom will release their energy in the form of photons. For all metals, the wavelength of photons is different. And it came back to the original state.
Due to different wavelengths of photons, each metal gives a different colored flame. Under the controlled condition, the concentration of the substance can be measure from the light intensity of the wavelength produced by atoms.
Various metal produces different wavelengths and flame color which is summarized in the below table.
| Metal | Emission Wavelength in (nm) | Flame Color |
| Sodium (Na) | 589 | Yellow |
| Barium (Ba) | 554 | Lime Green |
| Calcium (Ca) | 662 | Orange |
| Potassium (K) | 766 | Violet |
| Lithium (Li) | 670 | Red |
What is Reflectance Photometry?
A reflectance photometer measures the reflectance of light from the surface. The reflectance of light is a function of wavelength.
The white light is illuminated on the surface of a substance. The reflected light from a substance is measured after passing through a monochromator.
The color of the surface can be measure by measuring the wavelength of reflected light. This method is used in paint industries to characterized the color of a surface.
