[nine_k]

We of course can make LEDs of more or less any color. The current white LEDs are high-power blue LEDs that are covered by various phosphors to give a mix of colors for "full spectrum" illumination. Different color temperatures are produced by different mixes of phosphors. This is pretty similar to how the traditional luminescent (mercury vapor-based) lamps worked.

But different phosphors have different efficiency and price. LED lamps were first introduced for interior lighting, where sun-like spectrum is welcome. Such LEDs were produced en masse and relatively cheaply. So street lighting naturally used them, because municipalities usually look for the cheapest viable option.

We likely could produce high-power narrow-spectrum orange LEDs if there was a large market for the economies of scale to kick in. You can buy deep orange LED lamps today (look for color temperature 1800K or 1600K, "amber"), but they are more expensive, because they are niche.

[josephg]

> Different color temperatures are produced by different mixes of phosphors.

We can make LED light appear to be any given colour by mixing multiple LEDs. But mixed colour isn't the same as pure colour, made from a single spectra of light. Nor is it the same as true broad spectrum light - like we get from black-body radiation like the sun, or a tungsten bulb.

Its hard to tell the difference just by looking at a light. But different kinds of lights - even lights which look the same colour - will change what objects actually look like. And they probably have different effects on our sleep cycle and our low light vision. I was in a room once lit only by sodium vapour lights. The lights were yellow, but everything in the room (including me) appeared to be in greyscale. It was uncanny.

This is part of the reason why LED lights are still looked down on by a lot of old school photographers and film makers. Skin doesn't look as good under cheap LED lights.

[adrian_b]

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.

[functional_dev]

seafoam green choice was also influenced by eye rest studies... since our eyes are most sensitive to middle wavelengths. just keep the room dimmer without losing detail. It reduces fatigue for operators on long shifts.