I. Introduction
Light-emitting diodes (LEDs) are advanced elements of solid-state lighting devices. As compared to an incandescent filament lamp LEDs are capable to provide higher quantum yield and long-term stability [1]. However the degradation processes continue to be an important problem for LEDs. Another problem is lumen-price ratio. To solve this problem current density and therefore brightness of the LED-chip can be increased. Thus lumen-price ratio will by lower. Currently a lot of international manufacturers of LED-based lighting devices use this means.