Clear plastic sheet with (diamond, pyramid, prism, ...) pattern surface
on one side, used as a cover for fluorescent ceiling lights.
Cheap, available in 2 x 2 and 2 x 4 foot size.
Sean McGrath - Voice: 510.653.8387
Email: sean@oak.his.ucsf.EDU
Paper: 638 66th st, Oakland, Ca. 94609