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How to test glass transmittance?
Date:2013/7/22 12:55:54
Theoretical Introduction
When the light is incident on the glass, the performance of reflection, absorption and transmission of three kinds of properties.
The nature of the light through the glass, known as the "transmission" to the transmission rate is expressed.
When the light through the transparent or translucent body of luminous flux with the percentage of incident light.

Transmittance properties
When the light is incident on the glass, the performance of reflection, absorption and transmission of three kinds of properties.
The nature of the light through the glass, known as the "transmission" to the transmission rate is expressed.
Light is blocked by the glass, reflected at an angle, called "reflection", expressed in reflectance.
Light through the glass part of the light energy is lost, called "absorbent" to absorb rate is expressed.

Transmittance calculation methods
Glass absorptivity reflectance + + = 100% transmittance. Ordinary light transmittance of the glass is higher than the average 80% (for shading and insulation of heat-reflective glass, requires a high reflectance; for insulation, heat-absorbing glass glare effect, requires both absorb large amounts of infrared radiation, while maintaining good transmittance.)

Affect the light transmittance four areas:
Light through any medium in which the light transmittance (T), reflectance (R) and absorption (A) the conservation of energy between the following relation: T + R + Q = I to obtain a high transmittance it is necessary to reduce the light reflective surface of the glass, the glass absorption and scattering loss.
1,
Reflectance reflectance increases with the angle of incidence, but less than 40 degrees angle with the angle of incidence the reflectance did not change significantly, and when the incident angle is greater than 70 degrees, the reflectance increases sharply with increasing angle of incidence, the reflectance but also with the two difference in the refractive indices increases.
The glass and the air interface, the refractive index of air no = l, the refractive index of glass, n1 = 1.52, the refractive index fixed, so the impact is mainly reflected by the size of the angle of incidence.

2,
Visible absorption losses generally darker, its transparency coefficient is smaller.
In order to reduce the loss of light absorption glass can choose to use lighter glass, in addition to the glass with the thickness of the glass transmission loss decreases exponentially, visible light transmittance thickness smaller the smaller the loss.

3,
Scattering loss glass scattering loss mainly occurs in the composite glass, the glass can exist within some of the particles change the direction of light, part of the light can not be imaged and useless.
Light scattering loss depends on the size of the scattering point, the point when the size of the scattering of incident light wave has a wavelength of the same magnitude as the maximum scattering time, when the particle diameter of the wavelength of incident light is about 1/2 of the maximum scattering.
For organic materials exist within microparticles, the object observed through the glass on the same side of the object and the light source, there is a forward light scattering surface may cause haze and surface haze will result in the loss of contrast, thus affecting the clarity observed through the glass.

4,
Other factors affecting the panel transmittance of the light transmittance of different surface finish is not small, the same piece with the part of the panel operation is different from the hand of the measured surface condition can sometimes transmittance difference of 1% or more, the type of the panel is more likely to differences.
Finish should be mainly affect reflectivity.
Impurities in the glass raw material comes also affect transmission, such as ferric oxide, it should be because the absorption rate is affected.

Other Remarks
We are talking about are the visible light transmittance, there are other ultraviolet UV light transmittance, infrared IR light transmittance, and sometimes have to test industrial products, these are professional test equipment to help.
 
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