Hello

I´m trying to make a rendering engine which uses 'Glide' to show some objects.
This almost workes pretty good but there is still a problem.
To add some light I´m using the common algorithm to calculate the unit normal of a face then this vector is compared to the vector that comes from the light source to the object´s surface. Now the angle between these two vectors is calculated and the smaller the angle the 'more' the face is hit by the light. I´m not quite sure if this way
is the right one because sometimes it workes
and sometimes it doesn´t.

It's not clear what is the problem with your lighting. My guess is that you're not using any estaplished algorithm. You might consider taking a look at the tutorials in the programming section/graphics/shading Phong Lighting and specular Highlights. It's well written.