Illumination design is a job that is related to culture, and forms the bridge between illumination theories on civilization and illumination theories on culture. As a result of rapid developments in illumination technology, new light sources such as LEDs are now attracting attention, and the many calls for the elimination of incandescent lamps have led to a rather alarming situation. In illumination design, various types of light sources should be used in coordination to take advantage of their unique characteristics. In this sense, LEDs and incandescent lamps are light sources that should co-exist even in the future. In illumination design, what is more important than anything else is having the mindset to learn from natural lighting.