encoding directional lights with environment mapping

I am working on creating directional lights (runway lights) using spherical mapping. I use GL_POINTS for the lights with an associated normal. I notice this peculiar problem:The mapping is fine between -90 deg and +90 degree of the normal. In the +90 deg through 270 deg, I get the same map as between -90 to +90. Why is this?. If anyone is willing to help, I can post code to simulate this condition so that you could offer suggestions for correcting this problem.

[This message has been edited by vsranga (edited 05-14-2001).]