I made this one for an Aussie Yahoo Messenger (yo, Nobby!) buddy of mine.  This is a post HPV engine that uses the same positive phototropic visual cortex technique that the HPV uses. 

This SE uses 12 components including the solar cell!  Add feelers and you have a fully functioning photovore. 

A FLED can be substituted for R3 and you get basically the same results (I've built it both ways).