Lightless and Ultraviolet

Lightless adjective - Being without light or without much light.

Ultraviolet and lightless are semantically related. In some cases you can use "Ultraviolet" instead an adjective "Lightless".

Ultraviolet adjective - Having or employing wavelengths shorter than light but longer than X-rays; lying outside the visible spectrum at its violet end.

Lightless and ultraviolet are semantically related. Sometimes you can use "Lightless" instead an adjective "Ultraviolet".