How do I pick a surface mount LED?
Very subjective.   

Modern LED may be typically rated at
eg 30 cd at 15 degrees at 20 mA. 

1 mA usually noticeable but not bright
 5 mA nice and bright
 20 mA eye wateringly bright. almost painful.

Larger viewing angles decrease brightness with square of angle ratios.

Trying it and seeing is liable to be useful.



lumen = candela  x 2π x (1 - cos(A/2))

Or  

candela = lumen / (2π x (1 - cos(A/2) ) )

Where A is the full cone angle of the source.

A modern LCD screen is typically 300 lm/m^2 at the surface.

Have a look towards bottom of Wikipedia candela page - and ask questions.