A Simple Lighting Question?

Hi,

I have a 3D modelling app that uses OpenGL to render data. I’ve noticed that when I add an object to the scene the lighting changes, sometimes getting dimmer, sometimes brighter, sometime the lights seem to change the direction they are pointing in.

Anyone have any ideas why this is?

thanks in advance!

Wich 3D modelling app ?
Looks like bugs.

sorry i was a bit vague, the app is my own app, i can’t work out what i’m doing wrong.