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This research investigates whether a High Dynamic Range Imaging (HDRI) technique can accurately capture luminance values of a single LED chip. Previous studies show that a digital camera with exposure capability can be used as a luminance mapping tool in a wide range of luminance values with an accuracy of 10%. Previous work has also demonstrated the ability of HDRI to capture a rapidly-changing lighting environment with the sun. However these publications don’t investigate HDRI’s ability to capture a bright light source with a narrow light distribution (LED lighting).
Some of the existing concerns in LED technology today include low quality products on the market, inaccurate performance claims, and insufficient information on Solid-State Lighting (SSL) products. Division 2 in the International Commission on Illumination (CIE) (Physical Measurement of Light and Radiation) prepares the technical report (TC2-58) on measuring LED radiance and luminance; however progress has not yet been published. Manufacturers do not provide luminance data on their products even though luminance is the most important quantity in lighting design and illuminating engineering. It is one of the direct stimuli to vision, and many measures of performance and perception.
In this research two conventional luminance measurement methods of a single LED chip are implemented. One method involves the use of a luminance meter with a close-up lens, and the other method allows obtaining luminance through calculations from the illuminance measurements. Luminous intensity data can be determined using direct illuminance measurements taken in a created photometer. These data along with dimensions of an LED can then be used to calculate average luminance.
Varying apertures and shutter speeds in a digital camera allows obtaining a sequence of images with different exposures. These images are combined together using software to create an HDRI that gives pixel by pixel luminance values. The HDRI of a single LED chip is obtained using a neutral density filter. The results of this research indicate that the HDRI technique can capture luminance values of a single LED chip.
Adviser: Clarence Waters