Lux Meter-Photo Meter-Lux Meter Types & Construction-Lux Meter Working & Uses-Lux Meter Diagram

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.

Lux Meter-Photo Meter-Lux Meter Types & Construction
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
2. Photo Voltaic or Barrier Layer Cell Photometers

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.


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.

Lux Meter-Photo Meter-Lux Meter Types & Construction
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".

Lux Meter-Photo Meter-Lux Meter Types & Construction
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.

Lux Meter-Photo Meter-Lux Meter Types & Construction
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.

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