San Jose used sodium lamps for years in deference to Lick Observatory, which is on Mt. Hamilton about 15 miles east of the city. The biggest advantage of sodiu

San Jose used sodium lamps for years in deference to Lick Observatory, which is on Mt. Hamilton about 15 miles east of the city. The biggest advantage of sodium lights over incandescent for astronomy is that the spectral lines are very distinct and easy enough to filter out when doing scientific studies; incandescent, on the other hand, floods the spectrum broadly up to visible light. I believe LED lamps have similar properties to sodium, although I'm not sure how exact they are compared to sodium lamps—there might be greater variance in the spectra emitted due to material differences; whereas all sodium lamps are arcing through a common atomic element and have very predictable wavelengths.