When light emitting means such as a light emitting element (LED) is used for display or the like, typical usage conditions are approximately 1 V to 4 V for the drive voltage and approximately 20 mA for the drive current. With the recent development of short-wavelength LEDs which uses a GaN-based compound semiconductor and commercialization of solid light sources of full color, white color, etc., application of LEDs for illumination purposes has been considered. When an LED is used for illumination, there may be cases in which the LED is used under conditions other than the above-described conditions of 1 V-4 V of drive voltage and 20 mA of drive current. As a result, steps have been taken to enable a larger current to flow through the LED and to increase the light emission output. In order to flow a larger current, an area of a pn junction of the LED must be increased so that the current density is reduced.
When the LED is used as a light source for illumination, it is convenient to use an AC power supply and allow use with a drive voltage of 100 V or greater. In addition, if the same light emission output is to be obtained with supply of the same power, the power loss can be reduced by applying a high voltage while maintaining a low current value. In the LEDs of the related art, however, it is not always possible to sufficiently increase the drive voltage.
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