## 1 Introduction  
After the invention of blue light emitting diode (LED), most of the conventional lighting sources for general lighting applications are replaced by LED-based light sources. LED-based light sources have advantages to the conventional ones in terms of guaranteed longer life, lower power consumption, higher brightness, and less harmfulness for the environment [1; 2; 3; 4]. However, there are some disadvantages of LED-based light source. For example, heat generated from the junction in light emitting diode chip must be managed properly to prevent over-heating, which may damage the chip and/or cause degradation of materials in the package. As more light is produced from the high-power LED, industries keep developing more efficient heat-dissipating materials. Some are concerned about the use of high-power LED light sources which may raise potential risk to human health because of the blue spectrum from the LED [5]. LED itself is a kind of point light source; the glare of LED light source is another problem.  
Organic light-emitting diode (OLED) is one of the future-proof solid-state-based lighting sources since it may solve problems mentioned above. It has lower blue spectrum and surface light sources naturally. Moreover, it can create large lighting area even flexible and/or transparent panels. The OLED has relatively similar spectrum to natural sun light compared to that of LED and OLED light sources that are already showing great aesthetic potential without glare.  
Several companies already offer OLED products for general lighting applications. However current production lines are still small and prices are still high. But with mass production and higher efficacy, OLED will be one of the mainstream lighting sources in very near future. However, to replace conventional lighting with OLED products, long-term reliability characteristics of OLED panels and luminaires should be solved. There are some studies on long-term reliability characteristics of OLED light sources [6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. However, these studies focused on the light output degradation of OLED light sources mainly. In this paper, we have investigated long-term reliability characteristics of OLED panel and luminaries in terms of maintained optical and electrical characteristics such as lumen output, correlated color temperature (CCT), color rendering index (CRI), and operating voltage. To investigate the maintained characteristics dependences on the different panel shape, form factor, emitting surface size, and operating power, total twelve OLED panels with four different kinds and six OLED luminaires with two different kinds were analyzed up to six thousand hours for the general lighting applications. For example, to analyze the different panel shape effect on the long-term reliability with same emitting surface area, square shape panel (type A) and rectangle shape panel (type C) were tested. For the different form factor effect, flexible panel (type B) and rigid panel (type C) were compared. To check the emitting surface size dependence, small size panel (type C) and large size panel (type D) were analyzed. Finally, to investigate the operating power effect, high-power luminaire (type E) and low-power luminaire (type F) were studied.  
This paper is organized as follows. In Section 2, experimental setup and selected various kind of samples under test are described. In Section 3, measured results about the long-term optical and electrical characteristics of OLED panels and luminaires with operating time of six thousand hours are shown and analyzed. Luminous output maintenance, correlated color temperature, and color rendering index maintenance and operating voltage maintenance characteristics of OLED panels and luminaires are analyzed in this section. Then, discussion on the results such as light spectrum variation and color shift is followed in Section 4. Finally the conclusion of this paper is presented in Section 5.