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What Is Haze?
Definition of Haze
Haze is one of multiple quantities that can characterize a diffusive material. The other quantities are reflectance, transmittance, absorption, total integrated scattering (TIS) measurements, and bidirectional scattering distribution function (BSDF).
Haze is measured as the percentage of incident light scattered by more than 2.5 degrees from the specular from a surface or optical element. It can be measured in transmission and/or in reflection.
Figure 1. Haze is all scattered light in all directions without the specular.
Haze is expressed as a percentage (%), with no angular information; in other words, you do not know where the flux is going, but you know the quantity. The higher the percentage, the more blurred the image will be.
Figure 2. Example of 70% haze (left) and 50% haze (right).
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Why Is Haze Important to an Optical Design?
In optical design, to obtain accurate simulation results, you must have accurately defined optical surface and bulk properties. Geometry alone cannot determine the light distribution, because the optical material and surface properties determine how the energy and direction of the rays change. For this reason, it’s important to know as precisely as possible the optical characteristics of the materials you will be using. The best way to obtain precise characteristics is to measure the material directly and export the data to use in an optical software tool. Haze is one of the typical optical material performances you will measure.
What Solutions Does Keysight Offer?
Haze measurements are particularly difficult to perform because you need to separate the specularly reflected and transmitted incident light from the scattered light. These radiation patterns normally overlap and you cannot easily separate them using the geometry of the measurement equipment.
Keysight offers measurement services in a light- and temperature-controlled laboratory and provides two methods for measuring haze: measuring with an integrating sphere and calculating from BSDF measurements obtained by a goniometer.
Measuring with an Integrating Sphere
You can measure the haze of a material sample or surface using specially designed integrating spheres. In practice, you place the sample on the exit and then entrance port of an integrated sphere, and a laser source illuminates it to measure the reflectance (specular + scattered reflectance) and the transmittance (specular + scattered transmittance power), respectively. Perform the same measurement again after opening a port that permits the specular beam out of the integrating sphere, so that it is not included in the measurements of the diffuse transmittance power and the diffuse reflectance power.
Figure 3. Reflectance and transmittance measurement illustrations showing specular rejection in transmission and reflection.
Calculating from Keysight REFLET 180S BSDF Measurements
You can also calculate haze from BSDF measurements, as shown in the following two formulas:
Where:
- θd is the scattering angle of the detector
- φd is the azimuthal angle of the detector
- θi is the scattering angle of the source
- φi is the azimuthal angle of the source
- θdSpecular max and θdSpecular min are the limits of the specular part of the BSDF
You can perform BSDF measurements with the Keysight REFLET 180S goniometer. The accuracy depends on the resolution of the measurements, and the different angular resolutions of these instruments allow you to extract the specular part from BSDF measurements with varying degrees of accuracy.
| REFLET 180S | |
|---|---|
| Type | BRDF/BTDF |
| Dynamic range | 109 |
| Wavelength range | 400 nm to 1700 nm |
| Incident angles | Tunable: +90° to –90° |
| Angular range | Full sphere |
| Angular accuracy | < 0.1° |
| Repeatability | < 1% |
| Weight | 80 kg |
Explore Keysight’s Optical Measurement Services and Solutions
We offer a comprehensive suite of hardware solutions, including the REFLET 180s, designed to deliver precise light scattering data for materials and media in optical systems. These tools enable you to measure your own optical samples and seamlessly import custom data into Keysight's advanced optical design software.
For projects requiring specialized support, our optical experts provide custom measurement services to help you characterize light behavior, diagnose defects, and build accurate digital twins.
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