In his beautiful paper, Hasan Fakhruddin reported observations of mirror-like reflections in the rough surface of a ground glass plate. Similar effects have been recently employed for metrology of the roughness of optical diffusers used in modern light emitting device illumination systems. We report the observations of specular reflection in nontransparent rough surfaces at oblique angles, where roughness was treated as a variable. We present a simple trigonometry-based model explaining the observed phenomenon, which we experimentally validated using aluminum surfaces that have controlled roughness. The reported demonstration requires no special equipment, other than cellphone cameras, dielectric or metal plate, and sandpaper, and serves as an introduction to wave optics. This activity can be used to get further insight into everyday applications of wave optics for students already familiar with wave optics fundamentals.

1.
Hasan
Fakhruddin
, “
Specular reflection from a rough surface
,”
Phys. Teach.
41
,
206
207
(
April
2003
).
2.
Wojciech
Walecki
and
Peter
Walecki
, “
Robust diffuser and roughness metrology tool for LED manufacturing
,” in
SPIE OPTO
(
International Society for Optics and Photonics
,
2015
), p.
93830W
.
3.
Part 8340 purchased from 80/20 Inc.
,
Columbia City, IN
. https://8020.net/shop/8340.html
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