Methods for decreasing uncertainties in LED photometry

Abstract

Abstract. Even though energy-efficient and sustainable solutions, such as light emitting diodes (LEDs), have become popular in general lighting, mainly incandescent lamps are used as measurement standards in photometry. Optical properties of the LED lamps together with the often unstable built-in power converters bring challenges to NMIs and testing laboratories. Due to the narrow and complicated spectra of the LED lamps, the uncertainties of traditional photometers calibrated by incandescent lamps tend to increase when LED lamps are measured. Switching from an incandescent lamp to an LED-based calibration source would decrease the uncertainty related to the spectral mismatch correction. LED-based photometric standard lamps would also have other benefits, such as long lifetime and good temporal stability. Moreover, as spectra of white LED lamps are limited to the visible wavelength range, a novel method for illuminance measurements based on the Predictable Quantum Efficient Detector (PQED) can be used to characterize these standard lamps with luminous flux uncertainties significantly below 1 % (k = 2) at NMIs. The method eliminates the need of photometric filters in realization of the illuminance unit. Instead, the photometric weighting is carried out numerically using a separately measured relative spectrum of the source. Well characterized LED-based calibration lamps, together with improved electrical power measurement, would reduce measurement uncertainties of illuminance, luminous intensity, luminous flux and luminous efficacy measurements of LED lamps at NMIs and testing laboratories. This would have a high impact on the development of energy-efficient LED lamps and on the assessment of the energy saving potential of solid state lighting. It is also shown, that recent advances in illuminance and electrical power measurement will enable luminous efficacy measurements of LED lamps with uncertainty well below the present state-of-the-art level of about 1 % (k = 2).

Photometric and colorimetric analysis of light emitting diode luminaires for interior lighting design

“…Other authors are of the opinion that it is often difficult to achieve a good level of accuracy in photometric or radiometric measurements of LEDs due to uncertainties within measuring equipment and inadequate test setups 19,20 . Some authors claim that due to the narrow and complicated spectrum of LED lamps, the uncertainties of traditional photometers calibrated for incandescent lamps tend to increase when measuring LEDs 21 …”

“…Some recently published articles stated that the photometers currently used to measure incandescent light sources, halogens, and mercury vapor must be adapted to the different emission conditions of LEDs compared to previous luminaires 6,21‐25 . Kokka et al 24 performed colorimetric and photometric measurements of new white LEDs measuring 1516 LED products calculating eight representative spectral distributions for LED light sources related to color temperature categories.…”

Intelligent LED Certification System in Mass Production

“…The analytical calculation approach is the most common. This approach does not consider the entire set of changing parameters [ 13 ], which reduces its accuracy. The approach based on the direct measurement of the LED luminous flux [ 20 ] also has insufficient accuracy, since it does not consider the conversion of the luminous flux by the LED lens and does not investigate the effect of changing the temperature of the semiconductor crystal.…”

“…These applications lead to rather stringent requirements for the optical characteristics and efficiency of LEDs [ 12 ]. High quality is required when creating LED-based calibration lamps [ 13 ]. The studies presented in publication [ 14 ] proposed a method based on Zernike polynomials for characterizing the photometric values of LEDs and measuring the angular distribution of luminous intensity, total luminous flux, inhomogeneity, anisotropy and direction of the optical axis.…”

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

“…Further, when an LED lamp is used as the external source in the calibration procedure of the integrating sphere, the uncertainties due to spectral mismatch are also reduced [10]. These improvements in the measurement of luminous flux and recent improvements in the measurement of the electrical power [35,36] are discussed in [37]. After implementing these improvements and the reduced uncertainty of illuminance measurement due to improved aperture area measurement discussed in this paper, an uncertainty around 0.5 % (k = 2) in the luminous efficacy measurement of LED lamps could be achieved.…”