The guidelines come in a 13-minute video produced by the Independent Television Commission warning advertising creatives and programme makers about the dangers of flickering lights or patterns to people at risk from photosensitive epilepsy.
The ITC issued its first guidelines in 1994 after reports that a commercial for Golden Wonder Pot Noodles had caused seizures in three people.
One of the worst incidents occurred in Japan in 1997, when a four-second sequence in a Pokemon cartoon resulted in 685 children being admitted to hospital, most of them having suffered seizures.
The ITC's guidelines are kept under constant review by a working group, which includes its own staff and medical experts.
Louise McMurchie, the ITC policy adviser on photosensitive epilepsy, said: "We understand the production community's desire to engage viewers, and our aim is to help them to manage risk without restricting creativity."
ITC experts agree that, because TV is a flickering medium, it is impossible to fully eliminate its risk of causing convulsions. They also point out that a sequence of flashing images lasting more than five seconds might pose a risk even though it complies with the guidelines.
The updated code warns advertisers to beware of rapidly changing image sequences such as fast cuts, if they result in the screen flashing. They also caution against the use of strips which change direction, oscillate, flash or reverse.