As shown in the Figure 1, an incident angle is fixed against the position of light source and sample surface, and a photodetector is rotated in the incident light area making an incident point at the center. At this stage, the intensity of reflected light is calculated at each angle of receiving light and the relation between rotation angle of photodetector and light income is shown in the form of spatial distribution, which is called ‘”Variable angle luminous intensity distribution”. For its indication, there are two ways using partial reflection luminous flux or surface brightness.
(1) Indication by partial reflection luminous flux
Regarding the incident luminous flux, when all the reflected light from the sample surface S is received, the effective sample surface for light receiving becomes “Scosφ”. Here, light receiving luminous flux “Iφ” can be indicated as the formula as shown below. For example, when the variable angle luminous intensity at the perfect diffuse surface is indicated using the partial reflection luminous flux, it will be as shown in the Figure 2-(a).
Iφ＝Ioρcosφ
(2) Indication by surface brightness
It is possible to measure surface brightness of sample by illuminating a broad portion of sample surface at certain angle and receiving its reflected light through certain aperture. Here, reflection intensity “Iφ” can be indicated as the formula shown below. For example, when the variable angle luminous intensity at the perfect diffuse surface is indicated using the surface brightness, it will be as shown in the Figure 2-(b).
Iφ＝Ioρ
[Figure 1] Basic concept of measuring variable angle luminous intensity distribution
![[Figure 1] Basic concept of measuring variable angle luminous intensity distribution](images/img_products29.jpg)
[Figure 2] Variable angle luminous intensity distribution at the perfect diffuse surface
![[Figure 2] Variable angle luminous intensity distribution at the perfect diffuse surface](images/img_products30.jpg)
