Tuesday, February 08, 2005

Sky spectrum in Chicago

Chicago city lighting is nearly universally high pressure sodium (HPS). The street grid is lit with 310W Crimebusters on main aterials, 200W cobras on alleys, and 90W on side streets. New lights that get put in are 400W cobras on aterials and 150W or 250W on side streets. (Damnit! Way too much light, way too much glare. Put in full-cutoff lights and you can drop the wattage in half and get the same amount of light).

University of Chicago lighting is different. Most pedestrian lighting is mercury vapor. Newer floodlights have been metal halide.

If I took a spectrum of the light pollution, I could measure the strength of a sodium line and a mercury line and compare them to determine how much light pollution is from campus sources versus the city.

For this sort of spectroscopy I don't need a telescope--just a camera, grating, slit, and lens.


Ceriouslighting said...

Yes, way more light than is necessary.

I am aware of a set of LED streetlights that were sold to City of Chicago, not sure which department, maybe an environmental group.
The product came from luxbright but I don't believe this company is still supplying.

We need a greater movement in this country to reduce light pollution, as the IDA is doing. There will be a real commercial LED luminaire for streets and parking garages in production in October. Food for thought.

Dean W. Armstrong said...

The thing is though, LEDs aren't very efficient. They are about as good as halogen incandescents. They are great for colored lighting applications, like traffic signals, but when you need to light something with an ok CRI, they are not useful. The first step is to show the city the approximately $10 million a year savings in switching to full cutoffs.

Ceriouslighting said...

No question about it, LEDs may never reach the efficacy now seen in the HID industry. But HID bulb fixtures are only 60% to 70% efficient and their ballasts eat up minimum 20% of the watts going in. But that's a trial now on-street with LED luminaires by other manufacture, will keep you posted.

The more important issue you mention is whether or not the City will actually reduce wattage if they did go to Full Cut Off. Most do not, they simply maintain same wattage. This FCO vs wattage is a huge concern and frequent topic at Outdoor Lighting Forum an interesting group you may like to visit.

Dean W. Armstrong said...

Thanks, I'll take a look.