These vague 'laws of discretion' really get me annoyed. So I deem it's not safe to stop (safer to quickly accelerate through) as I know my car and how well it brakes, how close or what type of vehicle is behind me etc.
The law is simple and clear. Amber means stop as long as it's safe to do so.
If you are too close to stop on the amber you don't need to accelerate to beat the red. Just keep going at the speed you were travelling at.
If you have enough time to accelerate to beat the red, you certainly have enough time to stop.
The problem is that when the lights turn amber, most of us are thinking about whether we can beat the red (because we don't WANT to stop), rather than if we can safely stop.