non-luminous flame

Burners are thus usually designed to produce a non-luminous flame.

A non-luminous flame is used, to avoid masking the test colour by the flame's own colour.

The flame does not provide much light itself, and so a more heat-efficient non-luminous flame is preferred.

Blue water gas (BWG) burns with a non-luminous flame which makes it unsuitable for lighting purposes.

The test involves introducing a sample of the element or compound to a hot, non-luminous flame, and observing the color of the flame that results.