A photometer is an instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Photometers measure: Illuminance, Irradiance, Light absorption Scattering of light, Reflection of light, Fluorescence, Phosphorescence, Luminescence. Photometers are made in many forms for various applications. They may be used directly, as in photography or in measuring glare, colour variation, reflectance, or other qualities, or they may be incorporated into such devices as densitometers, spectrographs, and telescopes.

2. The measurement of the intensity of brightness of light that
can be perceived by the human eye is called photometry.
Photometry is the science behind the measurement of
light, which is perceived in terms of brightness to the
human eye.

3. A photometer is a device that measures the
strength of electromagnetic radiation in the range
of infrared radiation to ultraviolet radiation,
including the visible part of the electromagnetic
spectrum.
Usually, a photometer converts light into electric
current by using a photoresistor, photomultiplier,
and photodiode.

4. Photometers examine how light interacts with reflective
materials.
The Photometers basically works on the principle of
Beer-Lambert’s Law.
Beer-Lambert Law helps us define the relationship
between the intensity of light and the exact quantity of
substance present in the unknown solution.

5. where,
A is the amount of light absorbed
C is the concentration of the absorbing component
Beer’s law was stated by August Beer which
states that
“When a monochromatic light passes through a
solution the absorbance is directly proportional
to the concentration of the components present
in the solution”.

6. Johann Heinrich Lambert stated Lambert law. It states that
“When a monochromatic light passes through a solution the
absorbance is directly proportional to the path length of
the solution”.
where,
A is the amount of light absorbed
b is the path length or band width

7. Beer –Lambert’s law states that
“When a monochromatic light passes through a solution the
absorbance is directly proportional to the concentration
and path length of the solution”.
where,
A is the amount of light absorbed
C is the concentration
b is the path length or band width
where,
A is the amount of light absorbed
C is the concentration
b is the path length or band width
ε is molar absorptivity constant

8. “ When a monochromatic light passes through a solution at a particular
wavelength some amount of light is absorbed by the solution”, and the
amount of light which is getting absorbed is called absorbance.
• Concentration of the sample is directly proportional to the Absorbance.
• But the Absorbance is negative logarithm of Transmittance.
where,
T is the transmittance
A is Absorbance
I is the transmitted light
I0 is incident light

9. “ when a monochromatic light passes through a solution at a particular wavelength some
amount of light is absorbed by the solution and remaining light is getting transmitted”, and
the amount of light which is getting transmitted is called Transmittance.
• Concentration of the sample is inversely proportional to the Transmittance.
• And the Transmittance is inversely proportional to Absorbance.
where,
T is the transmittance
I is the transmitted light
I0 is incident light

10. where,
A is the amount of light absorbed
C is the concentration
b is the path length or band width
ε is molar absorptivity constant
Molar Absorptivity
Molar absorptivity, also known as the molar extinction coefficient, measures how
well a chemical compound absorbs a given wavelength of light.
It is an intrinsic property of the chemical compounds.
The higher the molar absorptivity, the lower the concentration of compound.
The SI unit of molar absorption coefficient is the square meter per mole (m2/mol)

11. Absorption Maxima
It is a particular wavelength at which substance
absorbs maximum light in the form of photons.
The absorption maxima (λmax) is independent of
concentration.
The molar absorption coefficient is a measurement
of how strongly a substance absorbs light. The
larger its value, the greater the absorption.
It is used for quantitative estimation using Beer-
Lambert’s Law.