In general, a plurality of fluorescent lights are installed on a ceiling of an interior such as an office to light the interior. Fluorescent lights as light sources are relatively inexpensive but have a relatively short life span, and the brightness of the fluorescent lights decreases over time.
A radiation angle corresponding to an angle by which light is emitted is 120 degrees or more, and an interior space is illuminated at intensities of illumination which are similar as a whole.
In order to solve a problem of a fluorescent light as a light source, which has a relatively short life span and a brightness of which gradually decreases over time, technologies for employing LEDs having a very long life span and consuming low electric power have been developed.
As an example, lamps employing LEDs as light sources as in Korean Patent 10-1052457 illuminate an interior after the radiation angle of light emitted from the LEDs thereof is widened to 120 degrees or more by employing a diffusion plate or a lens.
However, in the space lighting method according to the related art, an energy saving effect cannot be obtained while LEDs of a high efficiency are used. Accordingly, an LED surface light emitting device for replacing an existing fluorescent light is adapted to illuminate an entire interior space, and does not consider a relationship between an intensity of horizontal illumination and an intensity of vertical illumination.
When a diffusion plate or a lens is used, loss of light cannot be avoided, and accordingly, higher electric power cannot help being used for the same intensity of illumination.
Further, according to the related art, a reflection plate is provided on the rear side of a light source, a lighting device cannot be easily carried and installed because a weight thereof is relatively heavy due to a metal frame for fixing a substrate, and the lighting device cannot be easily installed and maintained because a safety accident should be prevented by firmly fixing the lighting device such that the light device does not fall when being installed on the ceiling.
In addition, according to the related art, the above-described indoor LED lighting devices employing a metal frame should be individually installed, and electric power should be supplied to each indoor LED light device. Accordingly, much time is consumed in the installation operation.