> and contributes the most to obscuring the stars That part is not actually true. Any light will obscure the stars; if you want to compare different colors, it

> and contributes the most to obscuring the stars That part is not actually true. Any light will obscure the stars; if you want to compare different colors, it's the middle of the spectrum that contributes most, but the difference is small. As an amateur astronomer, the LED lights are a big problem because their light pollution is hard to filter out. Sodium is easy, it's nearly monochromatic, so a simple filter will remove most of it. Mercury is not super-hard, the spectrum is not very broad and it's pretty uneven. But LEDs have a broad, even spectrum, which is impossible to filter out.