A type of close binary system in which the variations arise largely from non-uniform surface brightness caused by the reflection effect; abbr. R. The amplitude may be 0.5–1.0 mag. even when (as in many cases) eclipses are absent. A notable example is KV Velorum, also known as LSS 2018, which lies at the centre of a planetary nebula; it ranges from mag. 11.8 to 12.3 every 8.6 hours.