Colour in the Environment

The sky, the sea, snow, fog and sunset each change colour for a physical reason, and so do the places people look at colour: galleries, shops, stages and night-time streets. This section explains what physically changes in each setting and what only appears to.

Illuminance and colour-temperature figures are typical ranges from cited sources, not measurements of any particular place. Biological colour — plumage, flowers, camouflage — lives in Nature.

15 topics · 49 evidence-labelled claims · 23 sources

Tools

Light in different environments

Sky and atmosphere

Scattering, sunsets, rainbows, aurora and clouds.

Why is the sky blue and not violet?Air molecules are far smaller than the wavelength of light and scatter it in proportion to roughly the inverse fourth power of wa…Why are sunsets red and orange?When the sun is low its light crosses far more atmosphere to reach you, and along that long path Rayleigh scattering strips out v…Why are clouds white, and why do some turn grey or dark?Cloud droplets are comparable to or larger than the wavelengths of visible light, so they scatter all colours almost equally (Mie…Why does a rainbow always appear at the same angle, and what are the faint extra bands?Sunlight refracted into a raindrop, reflected once off the back and refracted out again concentrates at about 40–42° from the poi…What makes the aurora green, red, blue and purple?Aurora is light emitted by atoms and molecules in the upper atmosphere when energetic particles from space excite them.What causes golden hour and blue hour light?Golden hour is the period when the sun is low but above the horizon: its beam is reddened by a long atmospheric path and strikes…Why do colours look flatter and truer on an overcast day?A cloud layer turns the whole sky into a large, fairly neutral diffuser.Why do fog and haze wash out colours, and why do distant hills look blue?Fog droplets scatter all wavelengths almost equally, adding white light between you and everything you look at, so contrast and s…What happens to the colour of light under trees?Leaves absorb blue and red strongly for photosynthesis and let green and far-red through or reflect them, so light in canopy shad…

Water, snow and ice

Absorption and scattering in water and ice.

Why do colours disappear with depth underwater, starting with red?Water itself absorbs light weakly in the red through vibrations of its molecules, and over metres of water that absorption remove…Why is snow white on the surface but blue in holes, crevasses and glaciers?Snow is a jumble of ice grains and air: light bounces off countless surfaces and comes back out almost unchanged, so it looks whi…

Built settings

Galleries, shops, stages, screens and streets.

Why are museums so dimly lit, and how does that change the colours of the art?Light fades many pigments and dyes, and the damage builds up with illuminance multiplied by hours, so conservators limit light: t…How do shops light products, and what does it do to their colours?Shops light merchandise brightly and directionally, often with sources chosen to make colours look vivid rather than exactly true.How does stage lighting change the colour of costumes and sets?Stage light is deliberately coloured.Why do streets look different at night now that sodium lamps are being replaced by LEDs?Low-pressure sodium lamps emitted almost only the yellow sodium lines near 589 nm, so streets looked monochrome; high-pressure so…