Many linear flourescent lightbulb fixtures that I see have this series of transversal fins, such as in this picture: http://www.bizrice.com/upload/20130409/T5_14w_embeded_linear_fluorescent_louver_light.jpg. What are they for? They are certainly not for efficiency, as the lamp would be more illuminating without them. My best guess is that they mitigate glare if you look at them from certain distant angles. Anybody can think of another reason?