This light pollution filter is made of a special glass called didymium glass, with multi coating
This filter can significantly reduce the transmission of light from sodium vapor and mercury vapor lamps, which are mainly located in the range from 575nm to 600nm wavelengths, please refer to the chart below. Sodium vapor and mercury vapor lamps, commonly used in street lighting and industrial lighting, emit yellow and orange lights from the ground to the sky, ruining the nightscape views and pictures. So light with wavelengths from 575nm to 600nm is the main cause of light pollution.
This filter is able to greatly block the wavelengths from 575nm to 600nm, helping the camera get the correct color of the night sky and landscape. With the help of the filter, the images with the right color can also save a lot of bother from after-processing.
The filter does not add blue color or any other colors to the images, it just stops the wavelengths of the polluting lights. The contrast from the sky to the ground will be enhanced, and the true and beautiful colors of the landscape will be restored.
Usually using light pollution filters requires about 1 f stop of increased exposure. What is the difference on exposure time when using this filter?
The filter removed the yellow light pollution color cast but the rest of the image wasn't noticeably darker so I would say certainly less than one stop.