The Los Angeles Times weighed in on the Rosemont copper debate, focusing on the potential impacts of round the clock lighting for mining operations to the regions astronomical observatories. An innovative lighting plan prepared for Rosemont by the former head of the International Dark Skies Association, would reduce the estimated visible light from 21.7 million lumens, or the equivalent of about 12,000 houses, down to about 5.1 million lumens according to the Times, a 76% reduction. Using their numbers, this would be equivalent to the light from about 2,820 homes. The plan relies in part on using LED lights and focusing the light downward. [I've suggested that such an approach could be used at other mine sites as well] [Top, standard lighting approach demonstrates spill light in background and excessive sky glow above. Focused lighting system with high performance optics illuminates only the simulated waste rock dump area. From Monrad Engineering report on Rosemont]
The comparison raises the question as to how this compares to increased lighting in the Tucson area from the annual increase in number of houses. The Pima Association of Governments lists building permits in the Tucson metro area from going from 12,465 in 2005 to 3,331 in 2008 (latest numbers I could find). Construction is obviously down since then although I don't have the details. This also doesn't count business or industrial lighting additions. So, it looks like the Rosemont mine would add as much lighting as one-quarter of the new houses added annually prior to the recession, and perhaps as much as current construction would add.
In searching for a count of new housing in the area, one of the links that popped up was from the Green Valley News about plans to build 19,000 new housing units in the Sahuarita and Green Valley area, converting the world's largest irrigated pecan farm into a master community, west-northwest of the Santa Rita Mountains, where the Rosemont mine site is located. Using the numbers in the Times article, that would be equal to the lighting from 6.7 Rosemont mines.
Green Valley gave approval to the first phase of the project in March, although the news reports don't mention lighting concerns from the astronomical community being raised.
Interestingly, the developer is Farmers Investment Co. (FICO) which is one of the most vocal opponents of the Rosemont mine.