What Is a Transmission Meter?
A transmission meter is an instrument that measures the ratio of light transmitted through a glass object, for example. Conversely, it can also determine how much incident light is reflected or absorbed by the object being measured, such as glass.
Some materials are transparent, while others are colored. Transparent objects transmit light well, but not 100%.
For safety reasons, there may be legal standards that specify how much transmittance is required to ensure brightness.
Uses of Transmission Meters
When applying window film to automobiles, the law requires that the transmittance of the windshield and the driver’s and front passenger’s side glass must be at least 70%. If the transmittance is less than 70%, visibility is obstructed, which may lead to an accident. Therefore, after the windshield film is installed, the transmittance must be measured with a transmission meter to ensure that it is at least 70%.
A transmission meter is used to inspect not only automobiles but also various types of transparent films and glass after they are manufactured to determine if the transmittance is up to the specified standards.
Principle of Transmission Meters
There are roughly two types of transmittance measurement. One is to measure the transmittance of light as a whole, and the other is to measure the transmittance of each wavelength of light.
The measurement of overall light transmittance is applicable to automotive window films, for example, to check visibility for visibility purposes. The measurement system is simpler: first, calibration is performed without the object for which transmittance is to be measured, and then the transmittance is calculated by comparing the light intensity between the object and the measurement again. This is sufficient for rough confirmation of transmittance.
The type that measures transmittance at each wavelength can determine which wavelengths of light a material absorbs, and is used in research and development. In this case, the light source is divided into light of different wavelengths by spectroscopy, and the transmittance is measured by transmitting the light through the object. The major difference between this method and the whole light transmittance measurement method is that the results appear as a spectrum. The whole-light measurement method, on the other hand, only produces a percentage, making it a more complex system and more expensive.