Frequency ranges[edit]
A pulse of electromagnetic energy typically comprises many frequencies from DC (zero Hz) to some upper limit depending on the source. The range defined as EMP, sometimes referred to as "DC to daylight", excludes the highest frequencies comprising the optical (infrared, visible, ultraviolet) and ionizing (X and gamma rays) ranges.
Some types of EMP events can leave an optical trail, such as lightning and sparks, but these are side effects of the current flow through the air and are not part of the EMP itself.