LEDs for a Beacon: How far seen per "u-candela?"

Hello,

Posted this erroneously in the flashlight section, sorry.

Anyway, I need to construct a battery powered strobe beacon. How can I estimate the amount of micro-candelas (those "ucd" figures that LEDs are rated in) that I'll need to be seen from a given distance?

Daytime would require more "ucd" than night, I'd guess? Is there a rough figure for that?

If I should be looking for a better spec to convert to distance than the "ucd," please let me know.

(Any good online sources for this type of info? I hate to bog down BBS with seemingly basic questions, but I've dug and not come up with an answer so far ...)

Thanks very much,

Carl Berger