It is not too hard to get a grip of what integrating spheres are all about. They are simply optical devices featuring entrance and exit ports and have a reflective inner Lambertian coating which is highly reflective and functions in scattering and diffusing light. However, picking just the right one for your application is the tricky part made more so by the availability of a number of different specifications and configurations.
Your Application
One of the most important factors that are considered during the fitting of integration spheres is the application to be used with them. They include spectral measurements of Light-Emitting Diodes (LEDs), optical power measurement of lasers, and light sources and calibration of remote-sensing cameras through generation of light in a uniform field. Keep in mind that application spheres are grouped into 4 different categories including laser power measurements, reflectance and transmittance, uniform sources and lamp and light measurements.
Sizes
In the four basic categories of the integrated spheres apps, there are many different sizes of diameters, ranging from 1mm to 3m. If you need to measure laser power that is fast-pulsed, you need a small integrating sphere to ensure that the there is no negative effect on the rise time for detection. However, your integration sphere should not be less than 1m in diameter if you need to measure extremely large light sources producing multidirectional light. You may also need a large diameter if you want to use the sphere as a source of light in providing a large light-exposure field which is uniform.
Coatings
The kind of coating material used determines the reflectivity of the integrating sphere. In turn the level of reflectivity determines the quality of integration and accuracy of the measurement. The higher it is, the better the results it will achieve.
Powder or spray-on coatings rely on the wavelength range and the environment it is used in. Usually, barium sulfate which is based with a binder is used as a coating in the visible region. Near-infrared (NIR) to mid-infrared (IR) applications, however, commonly use diffuse gold coatings. Polytetrafluoroethylene (Teflon), which is sintered, is best suited for harsh environmental conditions.
Configurations
After putting all other factors into consideration, you cannot afford to leave out the configurations. You need to consider the number of detector and entrance ports to be used. In addition, you will have to give a thought to the requirements of baffles especially if the detector needs to be protected against damage from direct sources of light. However, you can leave them out if the measurements involve laser-diode with high divergence, instead position the detector near the entrance port to remove the initial hot light spot. This reduces the likelihood of saturation or damage to the photodiode.
Final Thoughts
Remember, Integrated Spheres have several great advantages over the ordinary power meters. One of the most important ones is the fact that their response to angular and spatial information is uniform which qualifies them for measuring diodes with angular divergence. Additionally, their attenuation is uniform; meaning that there is less likelihood of damage if the power level of the source is too high.