How to read this chart?

How to read this chart?

• The horizontal axis is the Wavelength in Nanometers (nm). 400nm is deep blue, at 520nm the human eye senses green and at 600nm red. At 656nm is the famous "H-Alpha" emission line of hydrogen.
• The transmission in % is plotted on the vertical axis.
• The red line shows the transmission of the filter.
• Visual filters: The grey line in the background shows the relative sensitivity of the human eye at night. The maximum is at ~510nm and drops to longer and shorter wavelengths. You can easily see, that you can´t see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity at 656nm is 0% at night!
• Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.
• The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by see mercury (Hg) and sodium (Na), which are used in nearly all streetlights.
• The most important emission lines from nebulas are shown in green. The most important lines are from ionized Hydrogen (H-alpha and H-beta) and double ionized oyxgen (OIII) .

The major emission lines of artifical light pollution: | Hg 435,8nm | Hg 546,1nm | Hg 577,0nm | Hg 578,1nm | | Na 589,0nm | Na 589,6nm | Na 615,4nm | Na 616,1nm |

The major emission lines of nebulas: H-β 486,1nm | OIII 495,9nm | OIII 500,7nm | H-α 656,3nm