Lighting on triangles - every other one is darkish I have a mesh in Blender, imported from elsewhere. You can see individual triangles on it in a funny checkered pattern, like this:



This is consistent with a popular bug where every other triangle is inverted, and you see half of them from the inside and half from the outside. But if you enable normal display, all the normals are facing outwards, as expected.

The mesh is available at http://www.jishop.com/temp/4osh.blend . Can someone please take a look at it explain the effect?
The triangles are all being displayed in 'Shade Flat' mode, which is the default. To change this, go to edit mode and select all faces (hit 'A' once or twice, until all triangles are selected). Then Hit 'W' then select 'Shade Smooth'

[Shade Flat] mode is appropriate for modeling a faceted gemstone, or cut crystal glass, for example. Since blender cannot know ahead of time what type of shading you need, it defaults to 'Shade Flat'.