To measure the exact reflection or transmission behaviour of a passive sample with a sphere, there are several things to consider:

• Size of the sample (area)
• Uniformity of the sample surface
• Wavelength region of interest (Illumination source)

 

As the reflection of a surface is strongly light source or wavelength dependent, the choice of the illumination source is of high importance.

When strong light absorbing samples (dark samples) are measured, the dynamic range of the detector should be evaluated first as the reflected signal will be low. A light trap, in contrast, needs to be used with samples which reflect direct light.

In general the end user has to decide whether he wants to use:

• Reference method or
• Comparison method

 

For transmission measurements, a second integrating sphere is used and the sample is placed in between the two spheres. With this set up, reflection and transmission (with and without direct reflected light) can be measured at the same time. The integrating spheres are,depending on the wavelength range focused on, either coated with a gold coating (700nm to 2000nm) or a barium sulfate coating (250-2500nm) to obtain the lambertian properties. To ease the measurement procedure, there are several sample holders and accessories which can be added to the system.

A novel and unique method to measure BRDF and BTDF behaviour of passive samples is the Imaging Sphere principle of Radiant Imaging Inc. Without a black room required and within seconds BRDF/BTDF data is obtained.

For further information click here or contact us directly.

(Link zur IS SA)