Measured with the same custom-made integrating sphere

An integrating sphere is an optical sphere internally coated with a reflective material such that light shining into its input port would be complete diffused and uniform by the time it reaches its output port. An integrating sphere has an input port and an output port which is typically mated to a monochromator, sample chamber, or detector. A baffle between the output and input port is optionally available to assure no input light directly reaches the output port without first being diffused by the internal reflective coating. The light source can be placed inside the integrating sphere and sometimes it is used as a sample chamber itself. Due to the many reflective bounces a ray of light has to take before reaching the output port, efficiency is typically around 30%, although this can be more accurately estimated following an approximated equation in the Product Details section. Various internal reflective coatings can also be chosen (depending on spectral region required) and baffles and additional ports can also be ordered. The light that reaches the output port is completely diffused meaning it can reach the output port at any reflective angle.

A multifunctional setup based on the absolute integrating sphere method for measuring luminous flux of light emitting diodes (LEDs) is presented. The total luminous flux in 4pi and 2pi geometries and partial luminous flux with variable cone angle can be measured with the same custom-made integrating sphere. This assumes you can collect all light from all angles as normally you would then have to ratio the solid angle of collection to the light collected at all angles as well. If you are calculating the light that gets collected into a monochromator or detector, use the area of the monochromator or detector slit and not the actual output port area. A complete calibration procedure of the constructed integrating sphere photometer is presented as well as comparison measurements with a goniophotometer. The number of baffles of the sphere and area of ports was minimized. Only one absolute calibration of the integrating sphere photometer is needed for measuring LEDs in all three geometries. The sphere has three ports: an auxiliary port, a detector port, and a main port, located in the same hemisphere. The main port is used for the calibration of the sphere as well as for the LED under test. The spatial nonuniformity correction is needed only for LEDs with low directivity or having significant minor beams. The other hemisphere is free of ports. The expanded uncertainty (k=2) for the measurement setup varies between 4.6% and 1.2% depending on the measurement color, geometry, and the angular spread of the LED light beam.