光沢
こうたく · koutaku · JLPT N1 · noun
luster
💎 光 (light) + 沢 (sheen): light reflecting off a glossy surface
沢 here means sheen, so 光沢 is light plus sheen. Glossy photo paper is 光沢紙 (こうたくし), a term you will see at print shops.
光 — fire 火 (top) + person 儿 (bottom)
Originally a pictograph of a person with fire above their head, depicting a torchbearer or the radiance from a flame. The character evolved to mean 'light' or 'brightness' in general, and by extension 'glory' and 'to shine.' The modern top component is a stylized form of 火 (fire).