The phrase "be light" can have a variety of different meanings, depending on the context. Some synonyms that could be used to convey a similar idea might include "shine," "glow," or "illuminate." In a more physical sense, "be light" could refer to weight or heaviness, in which case synonyms might include "lightweight," "airy," or "feathery." Alternatively, "be light" might be used to suggest a lack of seriousness or gravity, in which case synonyms could include "playful," "lighthearted," or "flippant." Overall, the most effective synonym for "be light" will depend on the specific meaning and connotation that the phrase is intended to convey.