There are many ways to portray speed through illustration: speed lines, after-images, a blurred background, etc.
Some of these are simply artistic license upon a visual effect, rather than something literally perceived by the characters within the story (a common example, visually representing an Electro-Magnetic Pulse or otherwise invisible lasers).
For Flash, some of the above, ended-up translating into actual literal in-story powers... after-images used to illustrate movement, became a power Flash could use to project multiple copies of himself; a blurred background used to convey speed, became an actual place speedsters would go at speed.
Lightning falls in this latter category.
Lightning is tied to the Silver Age Flash's origin, name, and symbol. Yet, mostly doesn't play any other role in his powers. I'm fairly confident that even after Crisis, Barry and Wally did not count lightning as part of their power set.
Sometime during Wally's run, his speed started to be represented with crackling energy and lightning unseen by anyone else. Then at some point it became literal lightning, where he had to worry about it setting off sparks or acting as illumination. Then it became a whole other facet to the power set to the point that the CW's Flash throws lightning as an attack.
When was the first time Wally's speed was portrayed with lightning effects?
When was the first time those effects entered the story as literal lightning which could interact with the story?