Lucas shares its root with the Latin lux, light, and the name is often read as describing illumination in a literal sense -- clarity brought into a space rather than metaphorical enlightenment alone. It suggests someone whose presence tends to make things easier to see, plainly rather than dramatically.
When the Moon and lord of the ascendant shall be impedited by the lord of the 8th, the sick person hath cause to fear. - William Lilly (1602.-1681.)