Direct midday sun
32,000–100,000 lx · Order-of-magnitude range from a reference table; the solar illuminance above the atmosphere is about 127.5–133 klx, so ground-level direct sun is necessarily lower.
- What physically changes
- Very high illuminance with a hard directional beam; shadows are lit only by bluer skylight, so lit and shaded faces of one object receive different spectra.
- What only appears to change
- At this light level colours look at their most saturated and small differences are easiest to see; glare and specular highlights can hide surface colour entirely.
- For judging colour here
- The harshest test of a match: differences invisible indoors show up here. Judge out of the specular reflection and compare lit faces with lit faces.
How much does the colour of daylight change, and what are D50 and D65?
Open shade under a clear sky
10,000–25,000 lx · The reference table's range for full daylight without direct sun; order of magnitude only.
- What physically changes
- The sun's direct beam is removed, so the light is both dimmer and markedly bluer than sunlight.
- What only appears to change
- The eye adapts part of the way to the blue cast, so shade looks neutral in person while a camera on daylight white balance records it as blue.
- For judging colour here
- Whites and pale neutrals read cooler here than in sun; do not approve a warm white in open shade and expect it to look the same indoors.
Why is the sky blue and not violet?
Overcast daylight
100–1,000 lx · The reference table gives about 1,000 lux for an overcast day and about 100 lux for a very dark one; bright thin overcast can be considerably higher.
- What physically changes
- Light arrives from the whole sky with soft shadows; illuminance is one to two orders of magnitude below direct sun.
- What only appears to change
- Lower light reduces apparent saturation, and the absence of shadow makes surfaces look flatter.
- For judging colour here
- Close to the diffuse daylight that colour viewing standards simulate, which makes it a fair place to compare samples — but expect colours to look quieter than in sun.
Why do colours look flatter and truer on an overcast day?
Golden hour (low sun)
Not sourced · No sourced range; illuminance falls steeply as the sun nears the horizon and depends on haze.
- What physically changes
- The sun's beam reddens and weakens, and strikes vertical surfaces almost head-on; warm light and cool shadow coexist in one scene.
- What only appears to change
- Adaptation only partly discounts the warmth, so the scene reads as warm; the contrast between warm light and blue shadow is exaggerated perceptually.
- For judging colour here
- Flattering and unreliable. Warm colours glow and blues go grey; never approve a colour on the strength of evening sun alone.
What causes golden hour and blue hour light?
Blue hour (civil twilight)
Not sourced · No sourced range for the whole period; a reference table gives about 3.4 lux at the dark limit of civil twilight under a clear sky.
- What physically changes
- Illuminance drops by orders of magnitude within tens of minutes, and the remaining sky light is strongly blue because of ozone absorption.
- What only appears to change
- Vision moves towards rod-assisted (mesopic) seeing: reds darken before blues, and colour discrimination falls.
- For judging colour here
- Useless for judging colour. Reds look dark and blues bright relative to daylight, a change in the observer as much as in the light.
What causes golden hour and blue hour light?
Full moonlight
0.05–0.3 lx · Typical full-moon illuminance is about 0.05–0.1 lux at temperate latitudes; about 0.3 lux is a near-maximum reached only rarely.
- What physically changes
- Illuminance is about a millionth of direct sun.
- What only appears to change
- Rod vision dominates; hue discrimination largely disappears and the scene reads blue-grey even though the light is not blue — the Purkinje shift.
- For judging colour here
- Nothing about colour can be judged; the familiar 'blue moonlight' is a property of night vision, not of the light.
How does the eye keep colours stable when the light changes, and when does it fail?
Under a forest canopy
Not sourced · No sourced range; attenuation depends on canopy density and changes second by second as sunflecks move.
- What physically changes
- Chlorophyll absorbs blue and red, so the blue/green and red/far-red ratios fall; sunflecks restore a near-daylight spectrum in patches.
- What only appears to change
- Adaptation discounts much of the green cast, but skin and neutral objects still look slightly green-tinged and dull in deep shade.
- For judging colour here
- A mixed, mottled light: two sides of one object can be lit by different spectra. Move into a clearing before comparing colours.
What happens to the colour of light under trees?
Snowfield in sun
Not sourced · No sourced range; incident light is that of direct sun, but clean snow reflects most of it back, lighting surfaces from below as well as above.
- What physically changes
- Very high surrounding luminance and light from every direction; shadows and holes in snow are blue from skylight and from red absorption in the ice.
- What only appears to change
- The eye adapts to an extremely bright field, so other objects look darker and less saturated than they are.
- For judging colour here
- Colours look dim against the snow and shadows look blue; a camera's meter underexposes. Judge colour against a grey card, not by eye against the snow.
Why is snow white on the surface but blue in holes, crevasses and glaciers?
Underwater, the first few metres
Not sourced · Qualitative only; depends on water clarity, sun angle and surface state.
- What physically changes
- Water's vibrational overtone absorption removes red first; dissolved and suspended matter adds its own green or brown cast.
- What only appears to change
- Divers adapt to the cast and under-report it; a red object near the surface still reads red but duller.
- For judging colour here
- Colour is already shifting within arm's length. Any colour judged underwater needs artificial light at short range.
Why do colours disappear with depth underwater, starting with red?
Underwater, tens of metres
Not sourced · Qualitative only.
- What physically changes
- Most long-wavelength light has been absorbed, so red surfaces have nothing to reflect and look dark.
- What only appears to change
- The scene looks monochromatically blue-green; a torch reveals colours that were physically absent, not hidden.
- For judging colour here
- Any red or orange seen at this depth is being lit artificially. Photographs need strobes or heavy correction.
Why do colours disappear with depth underwater, starting with red?
Underwater, around 100 metres and below
Not sourced · Qualitative only; sunlight fades towards darkness with depth.
- What physically changes
- No red light arrives, so red animals reflect nothing and are effectively black and invisible.
- What only appears to change
- Vision is near its dim-light limit; what little colour remains is blue.
- For judging colour here
- Deep-sea red is camouflage. The colours seen in photographs are the photographer's lights.
Why do colours disappear with depth underwater, starting with red?