The integrating spheres are commonly used in conducting photometric and radiometric measurements. Photometers and radiometers measure the optical energy that is coming from numerous sources such as lasers, fluorescent materials, electrical discharge sources and even the sun. The radiometer merely measures the power of the source whereas the photometers measure the power of the source the way the human eye perceives it.
They include SWIR integrating sphere, low-light integrating sphere, high-light integrating sphere, UV integrating sphere and calibrated output integrating sphere.
The Uses of Integrating Spheres
The integrating spheres measure the amount of light or power that comes from all the directions of a particular light source. The wavelength ranges include the Visible, SWIR, and UV. For instance, the sphere that has got a silicon photodiode are recommended for the measurements that range 400-1100 nm, whereas the models that have got an InGaAs detectors are suitable for the measurements ranging 800 – 1650 nm. The UV version, on the other hand, is optimized for the wavelengths between the ranges of 200 – 400 nm even though it may be calibrated to 1100 nm.
The integrating sphere is effective due to its spherical shape that integrates the light in the sphere, thereby making it easier to be captured and measured. The capabilities of the integrating sphere eliminate the inaccuracies that result from the directional characteristics of the sources of light.
The integrating sources of the spheres are made up of the sphere of varied sizes; baffles that stop the direct path of the source of light projecting from the source to the detectors; ports that allow the entrance and exit; and the specific coating for the interior of the sphere. There are different coatings that are used for different wavelengths. For example, gold is ideal for the IR spectrum whereas PTFE/Teflon is more appropriate for the visible SWIR and UV light measurement. The baffles that are used within the integrating sphere need to be coated with the same material just as the rest of the interior.
Application of Integrating Spheres
Integrating spheres are used for general purpose lighting. This includes automotive lighting, monochromatic laser lighting, solid-state lighting, LED lighting, LED backlighting as well as in architectural lighting. The integrating spheres measure the reflectance or rather transmittance of opaque samples, materials, infrared reflectance, and color properties.
Apart from measuring light outputs, the integrating spheres are also used in calibrating photometers, detectors, fiber optics, MTF testing, radiometers, and CCD cameras. The integrating sphere is also used in laser power measurements of high-powered infrared lasers and laser diode output characterization.
Conclusion
The broad range of integrating spheres, coming in different sizes and functionalities make them relevant for a wide range of applications. The most crucial factor to consider when choosing an integrating sphere is the maximum dimension of the light source that needs to be measured. In this case, whereas larger sources will need the use of larger integrating sphere, smaller sources will require smaller integrating spheres. This will greatly minimize any error in the measurement of the sources.