Solar array size important In Anne L. Fischer’s interesting article titled “Solar-heated bridges, roads” (February 2010, p. 38), she did not comment on the size of the solar array that would be needed. Because the roadway itself is a solar collector, and that area is not enough, the area of the collector would have to be larger than that of the roadway. She also did not mention the number of batteries needed. During a snowstorm, there is not much sunlight, so energy would have to have been saved from several days before. Edwin Norbeck Department of Physics and Astronomy University of Iowa Battle of the bulbs I enjoyed reading about the analysis of various light devices conducted by University of Pittsburgh researchers in the May issue (“LED streetlights shine in cradle-to-grave study,” p. 40). However, the investigators should have included incandescent bulbs in their comparison. Did they assume that incandescent bulbs are being mostly outlawed and are not politically correct? You included the rarely discussed environmental issues for manufacturing LED lights. LEDs are touted as the big solution, just as compact fluorescent lightbulbs (CFLs) were not so long ago. LEDs are not yet ready for widespread lighting, but are getting there. There should be more discussion about the manufacturing process and disposal of all of these lighting products. My experience with CFLs and tubular fluorescent bulbs is that they do not last nearly as long as claimed, can require time-consuming and costly ballast replacement, and are difficult to properly discard. What is the cost in time, transportation, energy and emissions to get rid of one CFL or a pair of 40-W fluorescent tubes? Few facilities will accept them. The local garbage company won’t pick them up. The incandescent bulb (e.g., 60 W), although not the most efficient operational choice, is cheap, easily manufactured, uses simple and mostly recyclable material (glass and aluminum), is not hazardous or toxic, and will not generate radio-frequency emissions. The total cost and effects of ownership should be considered. It is sad that the federal government does not allow people to make free choices in a free market. I am glad to see the city of Pittsburgh making a scientific study rather than spending a large amount of money irrationally. Oddly, carbon dioxide is treated as a harmful material, when it actually is the basis of life on Earth. Many people make that wrongful assumption and get on the bandwagon. This false idea will cost us huge amounts of money while some people gain huge amounts of money, for an infinitesimal change in the atmosphere. I believe that carbon dioxide is not a pollutant, but that its changing level in the atmosphere is a result of natural events. Too many people blindly accept theories from a small number of researchers who use suspicious methods. Science should be used in an honest way, not as a selective tool to support selfish political agendas. Dan Bosque San Bruno, Calif. Erratum A “Bright Ideas” product listing on page 80 of the May issue featuring the Genesis CX355-250 from Coherent Inc. should have read as follows: The Genesis CX355-250 from Coherent Inc., a solid-state CW ultraviolet laser, delivers more than 250 mW of output power. Its TEM00 output beam has an M2 value of <1.2, enabling optimum collimation and/or refocusing to a diffraction-limited spot, and its optically pumped semiconductor technology provides <0.5% noise, enabling OEM instruments to achieve good signal-to-noise characteristics. Applications include flow cytometry of live cells such as eggs, fertilized egg sorting, fluorescence-based confocal microscopy and 3-D prototyping such as stereolithography.