Xlib: connection to ":0.0" refused by server

[Nikhil Prabhakar <nipraonline@gmail.com>]

Hi all,
When opening emacs from terminal as "su" I'm getting this error:

debian:/home/nipra# emacs
Xlib: connection to ":0.0" refused by server
Xlib: No protocol specified

emacs: Cannot connect to X server :0.0.
Check the DISPLAY environment variable or use `-d'.
Also use the `xhost' program to verify that it is set to permit
connections from your machine.

While opening as normal user it works fine and with "su -" emacs open
up in terminal itself.

Regards
Nikhil Prabhakar