Television changed football, including the uniforms:

Television changed the game in many ways, both substantially and minutely. When the Bengals added uniform numbers to the sides of their jersey sleeves in 1980, they were following a slow, evolving uniform design trend that started in the mid-1960s as a result of the league's desire to become more viewer-friendly on television. In fact, uniform numbers that were added to sleeves or shoulders were referred to as "TV numbers," since their placement was intended to aid broadcast announcers and viewers in quickly identifying players from various camera angles. The league did not have a rule requiring teams to place TV numbers on uniforms until 1991, though by that time nearly all uniforms already had them. Also in 1980, the Bengals added uniform numbers to the team's helmet. Those numbers, however, were affixed for the purpose of quickly identifying which player a helmet belonged to if it was taken off and set down during a game. There still is no league rule requiring teams to place uniform numbers on helmets.

The new pants were official in 1980, but debuted in '79:

While the Bengals did not officially add the pants with the widened orange stripe to their uniform until 1980, that design actually appeared on a limited trial basis in 1979. The 1979 trials were not team-wide, with only a few players wearing the new design during select games that season.