دامنه طراحی بهینه با توجه به هزینه روشنایی حالت جامد مبتنی بر LED ، مصرف انرژی و قابلیت اطمینان

Design parameters of LED-based solid state lighting products are interdependent and the corresponding requirements are dictated by operating conditions. We propose a scheme to define optimum design domains of LED-based luminaires for a given light output requirement by taking cost, energy consumption and reliability into consideration. First three required data sets to define design domains are expressed as contour maps in terms of the forward current and the junction temperature (If and Tj): (1) face lumen and cost requirement as lumen/LED; (2) power consumption and energy requirement as luminaire efficacy (LE); and (3) reliability requirement as L70 lifetime. Then, the available domain of design solutions is defined as a common area that satisfies all the requirements of a luminaire. The proposed scheme is implemented for a wall wash light and the optimum design solutions are presented.

Recently LED-based luminaires have emerged rapidly for commercial and residential applications. For a required light output, the optimum design of a LED-based luminaire can be achieved by considering cost, energy consumption and reliability. Design considerations for LED-based luminaires are unique in that many design solutions are possible for the same required light output unlike the conventional light sources (e.g., compact florescent light, incandescent light, etc.). This is due to the well-known fact that the lumen output that each LED produces is a function of the driving current, If, as well as the junction temperature, Tj. Fig. 1 illustrates the details. The luminous flux of LEDs increases as the driving current increases, but the corresponding luminous efficacy decreases at a higher driving current because the luminous flux is not linearly proportional to a driving current. More importantly, when a higher driving current is used, heat flux becomes proportionally larger, resulting in a higher junction temperature. This increased junction temperature not only decreases the luminous flux but also significantly affects the rate of lumen maintenance (i.e., life time). A lower driving current can be utilized if more LEDs are used in the light engine of a luminaire. Yet this is often not the most desired solution due to the high cost of LEDs.

Design parameters of LED-based luminaires have been analyzed to suggest a design domain that optimizes cost, energy consumption and reliability. The required data sets were lumen/LED, luminaire efficacy, and L70 lifetime. The data sets were obtained by measuring the SPD of an LED as a function of forward current as well as junction temperature (If and Tj). The minimum junction temperature limit was also defined as a low bound of a valid design domain. The proposed scheme was implemented for a wall wash light and the optimum design solutions were presented. The scheme is general and can be applied to LED-based luminaires with either passive or active cooling solutions.