New Delhi, Oct. 30 -- a less disruptive bedroom, a better night's sleep or treatment for a persistent sleep disorder. Those are not interchangeable claims.

some research suggests better sleep quality, but not necessarily longer sleep or fewer awakenings. Its conclusion is more restrained than the prospect of a light that fixes the night.

That distinction matters before anyone buys a device. Feeling more rested is a worthwhile outcome, but it does not establish that a lamp treats insomnia. Nor does evidence from a particular therapy instrument automatically validate every red bulb, bedside light or panel sold under the same broad label.

Daniella Marchetti, a clinical health psychologist and behavioral sleep medicine specialist identifie...