What does 'luminous' refer to?

The term 'luminous' is often used to describe something that emits or reflects light in a way that is softly bright or radiant. This can refer to objects that glow, such as stars or certain types of lighting, as well as to colors that appear bright and vivid due to their reflective qualities. Generally, 'luminous' conveys a sense of warmth and gentleness in brightness, rather than harshness.

The other choices introduce contrasts that do not align with the definition of 'luminous.' For instance, describing something as dim and shadowy would directly contradict the idea of luminosity, as would characterizing it as dark and opaque. Blindingly bright might suggest an intensity that overshadows the subtler connotations of softness and warmth that 'luminous' encompasses. Thus, the selection of 'softly bright or radiant' encapsulates the true essence of the word.