| Class | Title | NELM | Approx.
SQM
mag/arcsec2 | Description | Color |
| 1 | Excellent
dark-sky site | 7.6–8.0 | 21.7–22.0 |
| Black |
| 2 | Typical trulydark site | 7.1–7.5 | 21.5–21.7 |
- the zodiacal light is distinctly yellowish and bright enough to cast shadows at dusk and dawn
- airglow may be weakly visible near horizon
- clouds are only visible as dark holes against the sky
- surroundings are barely visible silhouetted against the sky
- the summer Milky Way is highly structured
- many Messier objects and globular clusters are naked-eye objects
- M33 is easily seen with naked eye
- limiting magnitude with 12.5" reflector is 16.5
| Gray |
| 3 | Rural sky | 6.6–7.0 | 21.3–21.5 | the zodiacal light is striking in spring and autumn, and color is still visiblesome light pollution evident at the horizonclouds are illuminated near the horizon, dark overheadnearer surroundings are vaguely visiblethe summer Milky Way still appears complexM15, M4, M5, and M22 are naked-eye objectsM33 is easily visible with averted visionlimiting magnitude with 12.5" reflector is 16 | Blue |
| 4 | Rural/suburbantransition | 6.1–6.5 | 20.4–21.3 |
- the zodiacal light is still visible, but does not extend halfway to the zenith at dusk or dawn
- light pollution domes visible in several directions
- clouds are illuminated in the directions of the light sources, dark overhead
- surroundings are clearly visible, even at a distance
- the Milky Way well above the horizon is still impressive, but lacks detail
- M33 is a difficult averted vision object, only visible when high in the sky
- limiting magnitude with 12.5" reflector is 15.5
| Green/Yellow |
| 5 | Suburban sky | 5.6–6.0 | 19.1–20.4 | only hints of zodiacal light are seen on the best nights in autumn and springlight pollution is visible in most, if not all, directionsclouds are noticeably brighter than the skythe Milky Way is very weak or invisible near the horizon, and looks washed out overheadwhen it is half moon in a dark location the sky appears like this, but with the difference that the sky appears dark bluelimiting magnitude with 12.5" reflector is 15 | Orange |
| 6 | Brightsuburban sky | 5.1–5.5 | 18.0–19.1 |
- the zodiacal light is invisible
- light pollution makes the sky within 35° of the horizon glow grayish white
- clouds anywhere in the sky appear fairly bright
- even high clouds appear brighter than the sky background
- surroundings are easily visible
- the Milky Way is only visible near the zenith
- M33 is not visible, M31 is modestly apparent
- limiting magnitude with 12.5" reflector is 14.5
| Red |
| 7 | Suburban/urbantransition | 4.6–5.0 | 18.0–19.1 |
- light pollution makes the entire sky light gray
- strong light sources are evident in all directions
- clouds are brightly lit
- the Milky Way is nearly or totally invisible
- M31 and M44 may be glimpsed, but with no detail
- through a telescope, the brightest Messier objects are pale ghosts of their true selves
- when it is full moon in a dark location the sky appears like this, but with the difference that the sky appears blue
- limiting magnitude with 12.5" reflector is 14
| Red |
| 8 | City sky | 4.1–4.5 | <18.0 | the sky is light gray or orange – one can easily read stars forming familiar constellation patterns may be weak or invisibleM31 and M44 are barely glimpsed by an experienced observer on good nightseven with a telescope, only bright Messier objects can be detectedlimiting magnitude with 12.5" reflector is 13 | White |
| 9 | Inner-city sky | 4.0 | <18.0 | The sky is brilliantly litmany stars forming constellations are invisible and many fainter constellations are invisibleaside from the Pleiades, no Messier object is visible to the naked eyethe only objects to observe are the Moon, the planets, and a few of the brightest star clusters | White |
