A simple monochrome icon of an incandescent lightbulb.
<a rel="nofollow" class="external text" href="http://thenounproject.com/mr.sheepman/">Diego Carneiro</a>
CC BY 3.0
<a rel="nofollow" class="external text" href="http://thenounproject.com/noun/light-bulb/#icon-No2654">The Noun Project</a>