bright
粲 centers on brightness, especially a clear, shining quality. The meaning is straightforward and does not branch into unrelated senses.
粲 is thought to combine 米 (rice) with a phonetic element that also suggests brightness or purity. The exact historical development is uncertain, but the character likely expressed the idea of polished, gleaming rice.
The bottom 米 is rice, and the upper part looks like a shining light over it. Imagine polished white rice gleaming brightly under a lamp.
For サン, picture the bright sun (サン) shining on a bowl of polished rice: sun -> サン, and the rice glows brightly.