A Comparison of 2pi and 4pi Photometric Testing of Directional and Omnidirectional Sources in an Integrating Sphere

ABSTRACT

The U.S. Department of Energy Solid State Lighting program, as part of its support of standards and test methods development efforts, performed a series of integrating sphere comparison tests in 2pi and 4pi geometries. These tests were conducted to help characterize the potential difference between various test protocols for identical lighting products as this would relate to light emitting diode (LED) product testing. A total of 11 different directional and 11 different omnidirectional products were tested over three different testing protocols. These protocols represent real-world test conditions depending on varying laboratory equipment and calibration capabilities. The analysis of the data indicates that there are significant differences in how lamps are testing within the same integrating sphere using common industry accepted methods and calibration standards. The testing identified differences of 4% to 18% between common industry test formats for the particular lamp type and potential alternative formats. These results provide information on the differences in test formats and to help test method developers determine when it is important to more specifically define how tests must be conducted under different formats.

KEYWORDS:

• 2pi
• 4pi
• integrating
• photometric
• pi
• sphere