Optical aperture area determination for accurate illuminance and luminous efficacy measurements of LED lamps

Abstract

The measurement uncertainty of illuminance and, consequently, luminous flux and luminous efficacy of LED lamps can be reduced with a recently introduced method based on the predictable quantum efficient detector (PQED). One of the most critical factors affecting the measurement uncertainty with the PQED method is the determination of the aperture area. This paper describes an upgrade to an optical method for direct determination of aperture area where superposition of equally spaced Gaussian laser beams is used to form a uniform irradiance distribution. In practice, this is accomplished by scanning the aperture in front of an intensity-stabilized laser beam. In the upgraded method, the aperture is attached to the PQED and the whole package is transversely scanned relative to the laser beam. This has the benefit of having identical geometry in the laser scanning of the aperture area and in the actual photometric measurement. Further, the aperture and detector assembly does not have to be dismantled for the aperture calibration. However, due to small acceptance angle of the PQED, differences between the diffraction effects of an overfilling plane wave and of a combination of Gaussian laser beams at the circular aperture need to be taken into account. A numerical calculation method for studying these effects is discussed in this paper. The calculation utilizes the Rayleigh-Sommerfeld diffraction integral, which is applied to the geometry of the PQED and the aperture. Calculation results for various aperture diameters and two different aperture-to-detector distances are presented.

Characterization of predictable quantum efficient detector in terms of optical non-linearity in the visible to near-infrared range

“…The advantage of the PQED is that it can be operated at room temperature, can be portable, and it is easy to use compared to a cryogenic radiometer. The PQED has been utilized for high-accuracy optical measurements in the visible region, including a new realization of the photometric scale [16][17][18].…”

Linearity and nonlinearity of silicon photodiodes for accurate absolute optical flux measurements: a review

“…Based on their characteristics, various studies have examined the possibility of using commercial Si PDs as standard detectors of absolute optical flux [9][10][11][12][13]. By utilizing specially designed Si PDs, a predictable quantum efficient detector was also developed [14][15][16][17][18], and its feasibility as a primary standard was demonstrated [19][20][21][22]. Nevertheless, the true capability of an optical detector constructed using Si PDs as a primary standard is still a hot research topic [23][24][25].…”

Predictable quantum efficient detector for low optical flux measurements

“…The PQED consists of two custommade induced-junction silicon photodiodes [1,4] arranged in a wedged trap configuration. Over the last decade, the properties of the PQED have been studied comprehensively [1][2][3]5], and the PQED has been applied in various fields of optical metrology [6][7][8]. The characterization measurements have shown many appreciable properties, such as highcharge carrier collection efficiency [2,9], low reflectance [1], and linear response over seven orders of magnitude [2].…”