This article describes the types of Lux meters and Lux meters.
Also included are all the details of Optical Illumination Photo Meter, Trotter
Photo Meter, Macbeth Photo Meter, and Photovoltaic Cell or Barrier Photo Cell
Lux. Also included are working principles, textures, and diagrams.
Lux Meters
A lux meter is a portable instrument used to directly
measure the amount of illumination falling on a surface. Lux meters are also
often called photometers, light meters, or illumination meters.
In common parlance, light and illumination are used as synonyms.
Illumination is the amount of light that falls on a unit area of a surface. The
quantity will be one lux.
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| Lux Meters |
Types of Lux Meters
There are the following types of lux meters in terms of
working principle.
1. Optical Illumination Photo Meters
- Trotter Photo Meters
- Macbeth Illumino Meters
Optical Photo Meters
In optical photometers, the light coming in or measured is
compared to the light of the lamp inside the instrument. The different amounts
of light intensity are known in advance or its measurement is arranged. When
the light coming from outside becomes equal to the light of the lamp in the
instrument, then the amount of light in the lamp is noted. The use of these
meters is almost gone nowadays.
Trotter Photo Meters
The Trotter photometer is a very old illumination meter. It
is rarely used today. The range of this instrument is 0.1 to 42 lumens per
square meter. This photometer is named after the scientist who invented it.
Working Principle
This instrument works on the principle of Lamberts Cosine
Law. According to this law, illumination on a surface is directly proportional
to the cosine of the angle formed between the direction of light falling on
that surface and the normal of the surface.
This meter compares the light coming from two light sources.
One of them is inside the light source meter. Whose light is known. While the
light from another light source is determined by comparing the amount of light
known.
Construction
This photometer consists of a small box. Inside is a small
lamp on one side. The lamp "L" is supplied by a four-volt battery
"B". The light reflected from this mirror falls on the white surface
A. This surface is very light-absorbing. This level can be tilted right or
left. There is a test plate Q on the top side of the box. It shines on the
light that is meant to be measured. Its surface is also like A.
The light intensity in different directions varies according
to Cosine Law. A slot F is placed inside the test plate Q. Level A of which is
observed.
Working Method
The figure shows the outline of the said meter. The test
plate of the meter is placed in this place. The light of the place has to be
measured. Level A is then rotated by a cam (Cam) until the light level of A is
equal to the level of Q. A pointer is attached to level A. When A is rotated.
When it moves, it moves over the pre-calibrated scale S2. When the light at
both levels A and Q becomes equal, then the reading from the scale is noted.
The amount of light coming from outside. To calibrate the scale, the lamps are
marked on the scale by moving it up and down for different amounts of light.
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| Trotter Meters |
Macbeth Illuminometers
This instrument for the direct measurement of illumination
is more sensitive, more accurate, and more popular than trotter meters. Its
range is 5 to 250 lumens per square meter.
Working Method
This instrument works on the principle of Inverse Square
Law. According to which the illumination falling on a surface is suitable as
opposed to the square of the distance between the light source and the surface.
Construction and Working
The shape of this instrument is shown in the figure. It
consists of a prism, telescope, tube, transparent glass and screen, lamp, rack
and pinion, scale, dry battery milli-ampere meter, and a rheostat.
The "T" in this shape is a telescopic-type tube.
"H" is a manifesto, placed in a box in front of this telescope. On
the opposite end of the telescope is a tube "P", the open end of
which is directed towards the surface at which the light is to be measured.
This surface is a milky plate. On the left front of the manifesto is a
milky-colored glass screen or test plate "A". To the left of this
screen is a horizontal tube, one end of which (in front of the screen
"A") has a lamp L inside the closed box. This closed box has a small
window in front of the screen man "A". Is the light from the lamp
passes through this window and falls on the screen "A".
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| Macbeth Meter |
On the screen "A" the light coming from outside
also falls through the manifesto and also through the lamp. There is a Rack and
Pinion mechanism R to move the lamp back and forth. The lamp is slowly pushed
forward. Screen "A" is then monitored by I-Pice. When moving the lamp
forward (or backward) when the photometer head is in equilibrium, that is, the
light on both sides of the screen is exactly equal, the readings on the scale
"S" are noted. Is. Which is in lumens per square meter.
Photo Voltaic Cell or Barrier Layer Cell Photometers
Photometers are also often referred to as physical
photometers. It is more appropriate to use this photometer only where flex is
almost constant. Such photometers are not used in places where there is light.
Flex is changing fast. For example, television and film work, etc. These
photometers are now the most popular for direct measurement of illumination.
Working Principle
This instrument works on the principle of Photo Electric
Emission. According to this when light falls on a photoelectric cell, the flow
of electric current starts in it. Provided that this photoelectric is connected
to an electric circuit. Remember that the amount of current is directly
proportional to the intensity of light that is the amount of current changes as
the amount of light changes. Increasing the intensity of light falling on a
photoelectric cell increases the amount of current passing through the circuit.
And as the amount of light decreases, the amount of current passing through the
circuit decreases.
Construction and Working
The structure of this instrument is shown in the figure. This instrument consists of a photoelectric cell (which is a barrier liter type) and a sensitive micrometer. The photoelectric cell consists of a round iron plate. Selenium is covered with a thin layer of metal. This layer is very sensitive to light. This thin layer of selenium metal is covered with another thin layer of Gold (Platinum) G, which acts as a protective covering over the layer of selenium.
The function of the thin layer is to protect the bottom
layer). This layer of gold is so fine and transparent that the light falling on
it easily reaches the Gold Selenium Boundary. Due to photoelectric emissions,
electrons are emitted from the selenium layer. A sensitive micrometer M is a
connected parallel to the gold and iron plates so that current can pass through
it. This current, falling on this scale of Light or luminance is almost
directly proportional to the flux.
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| Photo Voltaic Meter |
Uses of Lux Meters
Such instruments are very comprehensive and lightweight and
are widely used for the direct measurement of illuminations in homes, offices,
business centers, laboratories, laboratories, and industries.
Thanks For Reading.
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