formed by two pictography characters: 日 - the Sun on the left, and 月 －the Moon on the right. If there are a Sun and a Moon at the same time, it is bright.
This is an ideogram character.
The bronze script of the character is
The top triangle and the curve is the moon, and the circle is the sun.
The big seal script of the character is
The left is the a window, the moonlight streamed in through the window, making the room bright.