Light pollution is a problem on night-photography, especially close to urban areas. Usually on locations where horizon is clearly visible; on seashores, open fields, etc. lights reflects to clouds, water and even on thin fog. That creates blooming effect of different kinds of color casts ruining the contrast and over all tonality. To solve this problem and ease the pain of the photographer, you can find multitude of different kinds of filters.
I have been using Haida filters for years and testing out their innovations. One major step was introduction of M10-filter holder and its drop-in filters (you can find my review here). Last winter Haida released also Clear-night filter M10 drop-in version for M10. So, short story first, here are couple of samplephotos ; two consecutive exposures shot on Sony A7R4 and Sony Gmaster 16-35/2.8. Exposure settings were ISO800, f/2.8, 10 seconds. Both are edited on Lightroom with identical settings, white balance set to 4000K. I will continue to do more testing during this wintertime, so stay tuned.
With clear-night filter
Without the filter