Home-made assembly includes penlight laser and light sensor duct-taped to a styrofoam platform shown at bottom of photo.
<a href="//commons.wikimedia.org/w/index.php?title=User:Sjilla&amp;action=edit&amp;redlink=1" class="new" title="User:Sjilla (page does not exist)">Sjilla</a>
<span class="int-own-work" lang="en">Own work</span>