Quote:
Originally Posted by O-tacular
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I've worked in the commercial lighting industry my entire career, here's my two cents.
Those articles are flawed. A) you're comparing two images taken at separate times with different cameras. Not apples to to apples. B) what those images show is what the ground looks like, not the sky above the ground.
Light pollution generally refers to artificial lighting lighting the sky, which LED does a much better job of limiting than traditional sources due to LED being a directional source. Ie. The light can only go in the direction the source faces. Traditional sources (in the case of roadway High Pressure Sodium and Metal Halide) are omni-directional sources meaning that the light from the bulb goes in all directions. The fixture has a reflector which directs the light where it's intended to go, but in most cases you still get light that go above the fixture. With LED fixtures you don't, unless it has been designed to do so.
The only way LED fixtures used for roadway can illuminate the sky is by reflecting off the ground, which in the case of pavement is typically less than 1%, usually closer to 0.1%.
The only real differences in those two images is that the colour of the illuminated surfaces has changed from amber to white, and on a photograph white will appear brighter.
LED has its cons, but increased light pollution isn't one of them. In fact most municipalities now require all public works light fixtures to be dark sky compliant, meaning zero light going above the fixture's horizontal.
There are also now much more stringent bylaws limiting light trespass, which basically means the light should only illuminate what it's intended to illuminate and nothing else. The reason these bylaws exist is because with LED this is now possible. With traditional sources it would've been much more difficult to achieve. LEED is the most stringent I've seen in this regard, they allow for a maximum of 1 lux on the property line and 0.1 lux 3m from the property line for private properties' site lighting. 0.1 lux is essentially what you're getting from moonlight.
The reason that this misconception of "LEDs are too bright" exists is because a lot people don't know how to design with LED properly. They overlight to 30-50 lux for site lights when IES recommendation is 10-20 lux. But that's because in the HPS and MH days you'd have a vig hotspot underneath the fixture which increased the overall average to 30-50. LEDs are nuch more uniform so the hotspot underneat the fixture is almost nonexistent, so 10-20 lux with LED is just as safe if not safer than 30-50 lux with HPS/MH due to the property bein much more uniformly illuminated.
All that said, the people above who said LED can mess with circadian rhythms are correct. LED has a spike in the blue spectrum which our bodies associate with daylight. Most pole lights jave an amber colour option, however the it's about 30% less efficient than 4000K light due tobextra layers of phosphor coating being required on the LED, so municipalities by and large haven't gone for that option until recently.
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