App note from OSRAM focuses on the measurement of LEDs and provides a fundamental understanding of optical measurement, calibration and measurement uncertainty. Link here (PDF)
With the recent rapid growth of the LED market and the development of its applications, LEDs have become more common. They can now be found in many new applications within the lighting community. These new applications have placed increasingly stringent demands on the measurement of LEDs. Hence, accuracy and precision are the keys in the optical measurement of LEDs. The radiometric, photometric and colorimetric quantities of the LEDs are typically derived from the optical measurement.