Spectrophotometer
is an analytical instrument used to measure the intensity of light as a
function of its wavelength. Spectrophotometer is a common tool in physics
laboratories, commonly used to measure light absorption. It measures
transmission or apparent reflectance of light as a function of wavelength.
Thus it allows precise analysis of colour or accurate comparison of luminous
intensities of two sources or specific wavelengths.
Classes of Spectrophotometer
The two major measurement classes of spectrophotometers are : Single beam
and Double beam spectrophotometers. There are certain differences between
the single beam and the double beam spectrophotometers. In the early days of
spectroscopy, double beam spectrophotometers were popular but now it is
thought that the single beam spectrophotometer is more advantageous.
- Single Beam Spectrophotometer : A single beam
spectrophotometer is used to measure the absolute light intensity.
- Double Beam Spectrophotometer : It is used to measure the
ratio of light intensities on two separate light paths.
How Do Spectrophotometers Work?
Spectrophotometers use a monochromator to analyze the spectrum. Some
spectrophotometers also use arrays of photo-sensors. Spectrophotometer
quantitatively evaluates the fraction of light that passes through a given
solution. A light from the lamp is guided through a monochromator, which
selects light of one particular wavelength out of the continuous spectrum.
This light is then passed through the sample that is being measured. As the
light passes through the sample, the intensity of the remaining light is
measured with a photo diode or other light sensor. Then the transmittance
for this wavelength is calculated.
The sequence of events in a spectrophotometer can be listed as follows:
- The light source enters the sample.
- The sample absorbs light.
- Then the detector detects that how much light is absorbed by the
sample.
- The detector then converts the amount of light absorbed by the sample
into a number.
- The numbers are plotted straight away, or are transmitted to a
computer to be further manipulated.
Components of a Spectrophotometer
A spectrophotometer consists of the following components :
- A equired Light Source
- A Monochromator
- An Appropriate Photomultiplier
- A Photo-detector
Applications of Spectrophotometer
The most common application of spectrophotometers is the measurement of
light absorption. They are used to measure diffuse or specular reflectance.
Spectrophotometer is an essential piece of equipment in any lab. It has
found applications in physiological, biochemical and molecular research.
Other Related Products
Reflectance Spectrophotometer
The reflectance spectrophotometer evaluates the amount of light reflected
by a surface as a function of wavelength to produce a reflectance spectrum.
In it the sample is illuminated with white light and calculate the amount of
light reflected by the sample at each wavelength interval. The reflected
light is passed through a monochromatic device that splits the light up into
separate wavelength intervals.
Spectroradiometers
Spectroradiometers
operate mostly like the visible region spectrophotometers. They are designed
to measure the spectral power distributions of illuminants. They are
generally used to evaluate and categorize lighting for sales by the
manufacturer, or for the customers to confirm the lamp they decided to
purchase is within their specifications. A spectroradiometer consists of a
light source, which shines onto the sample. The sample either transmits or
reflects the light. The detector detects how much light was reflected from
or transmitted through the sample. Then the amount of light transmitted or
reflected is converted into a number.
