Historically, cases used CCFL lighting and eventually single color LEDs as strips or in fans to illuminate their interior; modern cases use RGB LED lighting instead, often incorporated into case fans. To improve airflow while allowing RGB fans to be visible, many cases as of 2020 use metal meshes, without any external bays. Many include a PSU shroud and vertical gpu mounts. Some used to include holes to support external water cooling radiators. Cases with side windows may have side fans (on the window) as well, although it is uncommon for cases with glass windows to have side fans.