Abstract
Candles are one of the oldest lighting sources used by men, and they are still widely adopted in numberless occasions due to their warm and romantic giving emission. Nevertheless, few has full understanding about the characteristics of these widespread candles. Some myths remain unsolved regarding their color temperature, brightness, luminous efficiency, and their effects on human health. Hence, we have investigated these based on a series of paraffin wax candles with different wick. As learned experimentally, the candlelight shows in average a color temperature of 1,835 K. The brightness of candlelight is related to the braiding method and thread number of wick. A brightness of 1 cd is obtained from a tightly braided wick with thread number of 24; as for a loosely braided counterpart with thread number of 34, it is 2.2 cd. Overall speaking, the luminous efficacy is 0.27 lm/W for a candle with 96% paraffin wax, 2% microcrystalline wax, 2% stearin wax. From retina protection perspective, the candlelight has a maximum permissible exposure limit of 2,751 seconds, which is 2 times longer than the typical incandescent bulbs and warm-white compact fluorescent lamps (CFL; 2,595 K), and 3 times longer than warm-white light-emitting diodes (LED; 2,857 K). If used at night, the melatonin secretion suppression sensitivity of candlelight is 4.4%, which is 2 times better for melatonin secretion than that of the incandescent bulbs or warm-white LED, and 3 times better than that of the warm-white CFL. However, surprisingly, if compared with the candlelight style organic light-emitting diode (OLED), OLED is healthier than real candlelight: form retina protection and melatonin secretion perspective, the candlelight style OLED is 2 times safer and 3 times better than candlelight, respectively.