There are a variety of synonyms that can be used instead of the phrase "lights on." Some examples include: illuminated, lit up, brightened, glowing, shining, and radiating light. Other options could include: switched on, activated, ignited, flared up, sparked, and kindled. Each of these synonyms can convey slightly different shades of meaning or tone, so it's important to choose the one that is most appropriate for the situation. Whether you're describing a well-lit room, a glowing cityscape, or a single lamp switched on in the dark, there are plenty of creative ways to describe the presence of light in our lives.