Radiation of completely black body
<a href="https://sk.wikipedia.org/wiki/user:helix84" class="extiw" title="sk:user:helix84">helix84</a>
Own work based on: <a href="//commons.wikimedia.org/wiki/File:Blackbodygraph.png" title="File:Blackbodygraph.png">Blackbodygraph.png</a>