For light with a narrow spectrum, it is possible to make LEDs that emit that light with high-efficiency, for any color inside 2 ranges, one from near infrared to yellow (corresponding to semiconductor phosphides and arsenides) and one from blue to near ultraviolet (corresponding to semiconductor nitrides).

Only green LEDs have worse efficiency, because they must be made with semiconductors for which optimum efficiency is attained at either lower or higher light frequencies.

Lamps using high-efficiency amber LEDs with about the same color with sodium lamps could be made at an energetic efficiency at least double to that of white LED lamps.

The double factor comes from the visual sensitivity being double for the light at sodium color than for ideal white light.

In reality the energetic efficiency of such LED lamps should be more than double, because they do not have losses caused by conversion through fluorescence.