An integrating sphere is a hollow sphere coated internally with a matte finish, diffusing type material. The sphere is provided with ports or openings for an incoming beam of light, a sample specimen and a detector. Integrating spheres typically function as a light collection device. The collected light can then be used as a diffuse source or as a measurement device.
Integrating spheres operate by allowing light to enter the sphere through a sample port, then through multiple reflections is scattered uniformly around the interior of the sphere by the diffuse internal sphere coating. The diffused light is then detected at a port configured with a detector device.
Integrating sphere efficiency is determined mainly by the physical size of the sphere, the number of ports and most importantly the diffuse nature and reflectivity of the internal sphere coating.
Selection of the appropriate integrating sphere for your application typically can be determined by the following important factors:
Internal Sphere Coating:
The coating within the inside surface of the sphere must be a very efficient diffuse coating with high reflectance in order to deliver consistent integration and low absorption loss. Spectral Products uses a proprietary coating (Ba2SO4) to provide high diffuse reflectance of light over a wide wavelength range. Ba2SO4 is effective from 400nm up to 2500nm. For 500nm to 20µm applications, diffuse AuSpec gold-coated spheres are available.
The inside diameter of the sphere must be a minimum of 1.5 times larger than any device mounted within the sphere such as light source, sample or detector.
No more than 5% of a sphere internal surface area should be used for ports in order to provide proper sphere integration. If the number of ports exceeds 5%, a larger sphere should be considered. Contact Spectral Products for help determining surface to port area.
- Integrating spheres are used in many scientific research and industrial applications such as:
- Color Measurements
- Lamp Measurement Photometry
- Fluorescence Studies
- Reflectance of specular or scattering samples
- Laser & LED Measurements
- Uniform Light Source