You probably don't want to disable refraction from the global level though, since sometimes you may want to see refractive distortion in the clear plastic "glass" used for lights or on pieces of trimwork/badging. (Distance shots, perhaps not so much. But with close-ups it's noticable.) Just fix that property at the shader level.

Another option is to use the "=== Glass" instead of "Common Glass" in the refraction channel. (I wonder if that translates to "Window Glass" in the original French version? Seems to be what it's good for.) The difference between that and the top level shader refraction setting of none is pretty subtle though. (You have to look closely at the fresnel that affects transparancy and reflection and perhaps the caustic if it's enabled.) The quick render I made demonstrates the difference, starting out with Carrara's "Blue, Clear" and changing only the refraction setting.

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Barbequed Pixels?

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