Improvements to the IES TM-28-14 Lumen Maintenance Standard: A Generalized Acceleration Factor Approach for Solid-State Lighting

摘要

An SSL luminaire's lifetime is characterized in terms of lumen maintenance life. Lumen maintenance or lumen depreciation is the percentage decrease in the relative luminous flux from that of the original, pristine luminous flux value. Lumen maintenance life is the estimated operating time, in hours, when the desired failure threshold is projected to be reached at normal operating conditions. The accepted failure threshold of SSL luminaires is lumen maintenance of 70% -- a 30% reduction in the light output of the luminaire. Currently, the only industry accepted standard used to estimate the time to failure of an SSL luminaire, called L70, is the IES TM-28-14 (TM28) projection standard. TM28 utilizes the Arrhenius equation to determine SSL device specific reaction rates from thermally driven failure mechanisms used to characterize a single failure mode -- the relative change in the luminous flux output or 'light power' of the SSL luminaire. TM28 requires a minimum of 3000 hours of testing with a recommended 500 hour sampling period and necessitates two different temperature conditions, 25°C and 45°C are suggested, to determine the SSL lamp specific activation energy. One principal issue with TM28 is the lack of additional stresses or parameters needed to characterize non-temperature dependent failure mechanisms. Another principal issue with TM28 assumes one particular failure mode, lumen depreciation, adequately describes the failure of SSL luminaires. Additionally, TM28 is SSL luminaire specific for acceleration factors or lifetime estimations and is time intensive. The deficiencies in TM28 validate the need behind the development of acceleration techniques to quantify SSL reliability under a variety of environmental conditions. The methodologies developed in this work utilizes degradation data of SSL lamps under a variety of accelerated test conditions for the development of a novel generalized acceleration factor model for use with any SSL lamp. This will greatly reduce the time and effort needed to produce SSL acceleration factors for the future development of accurate lifetime predictions.