I clearly saw the combustion chambers in each engine lighting up, making a ring of bright dots.
I've seen that on a Trident. In 1974 when I was working at LHR, I was driving around the terminal for a couple of days with a propulsion engineeer. We were parking across the cul-de-sac from each departing Trident while he watched the start up with binoculars to see if the flame propagation was regular. You could see the flame move round the engine from can to can.