Three basic types of lighting fixtures

globe

These fixtures are considered ideal by many architects. They can look fine in daylight. However, during night their light shines mostly in your eyes and into space, with only a fraction of their light falling on the ground. People with eye disabilities may see nothing but the lamps.
with round belly
Lighting fixtures with a pronounced, visible globe are still taken as a matter-of-course by uninformed people. Even such fixtures cast too much light to the sky and burden people by glare. At least one third of the radiating light serves nothing else but pollution.
with horizontal glass

Just a fixture with a flat glass on the bottom directs the light properly. Having a row of such lamps ahead, you can really see your way and the sky can be full of stars even at the end of the city. (Even an old fixture can become good by discarding the diffusing bottom belly...)

 

Both fixtures casting most of their light downwards are shown without poles, as they can be mounted in many different ways.

Plots and text by Jeník Hollan, N. Copernicus Observatory and Planetarium in Brno, January 2001. For the source programmes in PostScript (and bitmaps *.png made from them by "convert") see directory http://amper.ped.muni.cz/~jhollan/light/schemata.