1. Full of effulgence; describing the emission of visible radiation: The night sky was the most luminous Jeff had seen during his vacation, simply glittering with starlight.

Max has a watch with a luminous face which can be seen when it is dark.

2. Emitting or reflecting lucency, with or without accompanying heat: The most luminous life in the sea tends to dazzle an eerie green under the night sky.
3. Immensely bright or brightly colored: The luminous illustration in the hand-printed text drew the reader's attention to the fine designs and complimentary colors.
4. Evaluated on the basis of the visual sensation produced in an observer rather than energy measurements: Sarah gave a luminous performance of the role as Marie in the first play of the summer season.

The ratio of the radiant energy sensed by the average human eye at a particular wavelength to that received: The ophthalmologist, Dr. McMahon, was requested to determine the luminous efficiency of his patient, Mr. Jones, who appeared to have difficulty perceiving particular colors.

The rate of flow of radiant energy, expressed by brightness that is emitted in a unit of solid angles by a uniform point source with intensities of one candela or the base unit of beaming intensity or the power emitted by a source of illumination: Dr. Young and the scientists measured the luminous flux using the latest equipment designed to indicate in lumen the rate or speed of light transmission.