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mcfly_c-137yesterday at 10:48 PM3 repliesview on HN

The monochromatic light emitted from sodium lamps is also close to the peak sensitivity of the human eye. Colours are not distinguishable, but contrast is much enhanced compared to “cooler” light sources.

*edit: but it’s the overwhelmingly larger lifespan (20-30k hrs) that led to the wide adoption as streetlights. And I guess, the same is true for the change to led today, because of less power consumption.


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jacobolustoday at 2:21 AM

It's not especially close to the peak sensitivity of the human eye (in either bright or dim conditions), but that's entirely okay. The goal should be to not affect people's level of dark adaptation.

If you use shorter ("bluer") wavelengths, as happens with white LEDs which consist of a blue LED + phosphor, it causes people's eyes to become bright adapted and effective night vision is ruined, causing people to have much worse vision in the shadows.

Also, if you use bluer light, the lights themselves cause dramatically more glare in peripheral vision, because the shorter-wavelength-sensitive "S" cone cells and rod cells are mostly absent from the fovea (center of the retina), and prevalent in the outer areas of the retina. This is why LED headlamps on cars are so obnoxious for drivers going the opposite direction.

Also, the LEDs clobber people's circadian rhythms and are extremely disruptive to wildlife.

Finally, the light pollution caused by the LEDs is much worse for seeing the stars, which is maybe not as important as the other harms, but still kind of sad.

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AriedKtoday at 6:21 AM

The power savings are minor btweeen LED and low presssure sodium lamps. The LED streetlights emit light along the full spectrum, the sodium lamps only at 589 nm. The LEDs are more controllable so smart dimming ( when there are no cars) is a perceived advantage.

eastboundtoday at 12:56 AM

Sodium lamps were deemed dangerous for driving” because they made it difficult for drivers to distinguish shapes, since they were different from day shapes. A kid in bright 1980ies colors (Little Red Hood) would look black under those lights.

LED was presented as a sharp improvement because of the large spectrum of white light.

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