The working principle of a haze meter or turbidity meter

Haze meter, also known as turbidity meter:
Haze indicates the degree to which transparent or semi transparent materials are not clear. It refers to the cloudy or cloudy appearance caused by light scattering inside or on the surface of a material. Expressed as a percentage of the ratio of scattered light flux to the light flux passing through the material. Usually, only scattered light flux that deviates from the direction of incident light by more than 2.5 degrees is used for calculating haze. Distance produces beauty, and the haze is also the same. Glass made of the same material has different haze, and the display effect is also different.

Working principle:
When a parallel beam of light is incident on a certain medium (such as transparent plastic), due to the non-uniformity of the optical properties of the material; Surface defects, uneven internal organization, presence of bubbles and impurities, etc. can cause the beam to change direction (diffusion and deflection), resulting in scattered light.

According to international regulations, the ratio of scattered light flux that deviates from the direction of incident light through the sample to transmitted light flux is expressed as a percentage, which is called haze. Samples with high haze will give a more blurry impression. When light passes through the sample, it also causes loss, that is, the transmitted light flux passing through the sample is always smaller than the incident light flux shining on the sample. The ratio of the two, expressed as a percentage, is internationally defined as transmittance. The reason for the decrease in transmittance is the reflection of light on the two surfaces of the sample and the absorption of light energy at all or part of the wavelength of the incident light by the sample.

But it should be noted that haze and transmittance are two concepts. Materials with high haze can have low light transmittance. If such materials are used for window glass, the room will appear bright during the day, but it also has concealment; If making a car windshield, it is obviously required that both are good for easy observation. In the process of testing the haze and transmittance of the sample, it is necessary to measure the incident luminous flux (T1), transmitted luminous flux (T2), instrument scattered luminous flux (T3), and sample scattered luminous flux (T4). The calculation method for transmittance and haze values is as follows:

Transmittance: Tt=T2/T1 × 100%

Haze: H=T4/Tt × 100%
When testing, when there is no incident light, the accepted luminous flux is 0. When there is no sample, all the incident light passes through, and the accepted luminous flux is 100, which is T1. At this point, a light trap is used to absorb the parallel light, and the received luminous flux is the scattered luminous flux T3 of the instrument; Then place the sample, and the instrument accepts a luminous flux of T2. If the parallel light is absorbed by a light trap, the luminous flux received by the instrument is the sum of the scattered luminous flux of the sample and the instrument, T4. The transmittance and haze values can be calculated based on the measured values of T1, T2, T3, and T4.

1. The calculation principle of haze
When a beam of parallel light from a standard “C” light source is vertically irradiated onto a transparent or semi transparent film, sheet, or plate, due to scattering caused by the interior and surface of the material, all the light passing through the object causes a portion of the parallel light to deviate from the incident direction by more than 2.5 °. The percentage of the scattered light flux Td to the light flux T2 of the passing material is:

2. The calculation principle of transmittance
Transmittance, expressed as a percentage of the ratio of the luminous flux passing through the material to the incident luminous flux. Usually, it refers to the ratio of the luminous flux T2 passing through a thin film, sheet, plate shaped transparent or semi transparent material vertically illuminated by a parallel beam of standard light source to the incident luminous flux T1 shining on the transparent material, which is:

If we compare light passing through glass to soldiers breaking through levels, the initial army and horses are called incident light flux T1. They have overcome obstacles and suffered casualties, while the remaining ones who have successfully entered levels are called T2. Among the soldiers who entered the border, in addition to those who continued to move with the army, some may also escape to all sides due to the impact of the battle. We refer to deserters who deviate from the direction of the army by 2.5 degrees as Td.

3. The relationship between haze and transmittance
Haze and transmittance are two important optical performance indicators of transparent materials. In packaging applications, hazy films may reduce consumers’ quality perception, such as the appearance of blurry packaging products. Generally speaking, materials with high transmittance have low haze values, and vice versa, but this is not entirely the case. Some materials have high light transmittance but high haze value, such as Frosted glass. So transmittance and haze value are two independent indicators.

Haze Meter – Turbidity Meter HM-100 conforms to both ASTM and ISO international standards ASTM D 1003, ISO 13468, ISO 14782, JIS K 7361 and JIS K 7136. It already includes a CNAS Calibrate Certificate.  It is no need to do warm-up, after instrument is calibrated, it can be used. And measurement time is only 1.5 seconds.

HM-100 Haze Meter/Turbidity Meter

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