Charalampos Kostoulas broke the deadlock before half-time, and Coventry City's afternoon fell apart after the break when Malick Yalcouye doubled the lead and Taiwo Awoniyi was sent off for an elbow on Maxim De Cuyper.
Pascal Gross converted the resulting penalty after Bobby Thomas fouled Kostoulas, before Lewis Dunk added a stunning 25-yard strike and Yasin Ayari completed the rout in stoppage time.
Speaking to Sky Sports, Lampard said the scoreline reflected the gap Coventry must close in the Premier League after their promotion from the Championship.
"We have to be realistic in this league. They are a good team," Lampard said. "We started well, the most disappointing goal is the second one and it was a mistake that you can't do at this level.
"Down to ten men it was a different game against a team with a lot of quality. The players gave everything until the end but it doesn't feel nice.
"We have to take some responsibility and understand these are the levels we need to raise to."
Lampard pointed to the difficulty of Coventry's opening fixtures, which included away trips to Arsenal and Manchester City either side of a home defeat to Hull City.
"We're four games into the season and we've played the two most difficult fixtures," he said. "It is more pressure and a lot of players have not been near that. I've been in this situation many times. I was more disappointed with Hull than today. It was a Brighton team that were very clinical."
Brighton boss Fabian Hurzeler was pleased with a controlled performance, praising his side's ruthlessness in front of goal.
"Every win away is something special in the Premier League," Hurzeler said. "The red card helps us, but Coventry were always dangerous from set pieces. We kept a clean sheet, and that's the most important thing, so a good overall performance."
Hurzeler singled out Lewis Dunk's strike and goalkeeper Bart Verbruggen's contribution to the clean sheet.
"We know he has a great technique with his right foot, and we know he has the courage, so I'm happy he gets his rewards," Hurzeler said of Dunk. "We have a great goalkeeper, big saves from him today."
The result lifts Brighton into the Premier League's top four, while Coventry remain bottom of the table without a point or a goal after four matches.