When an ambulance has its lights on but is silent (no siren), it generally means a lower-priority emergency or a situation where immediate clearing of traffic is not critical, but the ambulance still needs to be visible and move efficiently. This can happen when transporting a stable patient, during late- night transfers to avoid disturbing the community, or when responding alongside police who request a silent approach. Another reason could be to avoid distressing a patient on board whose condition might worsen with siren noise, or to protect vulnerable road users like cyclists or horse riders. In some cases, the silent approach is used to maintain calm at sensitive scenes or when the ambulance is transporting a deceased patient.

Thus, a silent ambulance with lights on is still an emergency vehicle that requires other road users to be aware and give way, but it indicates a situation where sirens are either not necessary or not appropriate at that moment.