The Voice final posed risk for people with photosensitive epilepsy
The incident, which generated one complaint, happened during the final of the singing contest broadcast on 4 April, when Emmanuel Nwamadi performed Somebody That I Used To Know.
Flashing lights between the frequencies of three and 30 Herz can trigger a seizure in a person with photosensitive epilepsy.
Ofcom said: 'The technical assessment of the flashing images in this performance found that on two occasions they failed to comply with the Photosensitive Epilepsy Guidance. Television broadcasters must take precautions to maintain a low level of risk to viewers who have photosensitive epilepsy.
'Where it is not reasonably practicable to follow the Ofcom guidance, and where broadcasters can demonstrate that the broadcasting of flashing lights and/or patterns is editorially justified, viewers should be given an adequate verbal and also, if appropriate, text warning at the start of the programme or programme item.'
Research into photosensitive epilepsy
A spokesperson for Epilepsy Society said: 'One in 20 people with epilepsy has photosensitive epilepsy. Flashing lights and flickering sunlight can trigger a seizure as can strobe lighting at nightclubs. People with this type of reflex epilepsy have to be ever mindful of lights around them and what they are watching on the television.
'Photosensitivity is a current area of research for us. Our researchers have recently been able to identify a genetic mutation which is a risk factor for some people with photosensitive epilepsy.'
Find out more about photosensitive epilepsy.
Read about our research into photosensitive epilepsy.