10000K — Blue Shade
Open shade under a clear sky — a color, not a light source
Around 10000K you are looking at the color of the clear blue sky itself. It exists in reef aquariums, stage lighting and photographic shade conditions, but effectively never as a functional white light.
Open 10000K in the visualizer- CIE 1931 x
- 0.2788
- CIE 1931 y
- 0.2920
- Locus
- CIE daylight (D-series)
- Category
- Daylight
10000K in four rooms
What it does well
- Correct spectrum for reef and marine aquarium keeping
- Convincing 'moonlight' and night-scene effect in stage and film lighting
- Dramatic architectural accent when contrasted with warm sources
- Matches open-shade daylight for specialised photographic work
What it costs you
- Not a usable white light — renders nearly every surface inaccurately
- Skin tones look grey and unhealthy
- Extreme blue content; the worst common option for evening exposure
- Very low perceived comfort; causes eye strain quickly
- Almost no general-purpose fixtures are made at this temperature
In practice
The blue sky on a clear day measures anywhere from 9000K to well over 15000K. It is not a white light source in any practical sense — it is a strongly blue illuminant, and objects lit only by it (a subject standing in open shade, out of direct sun) take on a pronounced cold cast that photographers spend real effort correcting.
In products, this range shows up in two places. Reef aquarium lighting uses 10000K and above because corals and their symbiotic algae respond to short-wavelength light, and because it visually recreates the spectrum at depth where longer wavelengths have been absorbed by water. Stage and architectural lighting uses it as a deliberate color effect — 'moonlight' on stage is almost always a deep blue rather than a dim white.
As general illumination it fails on every practical measure: colors are badly rendered, skin looks corpse-like, and the perceived brightness advantage of cooler light has long since reversed into discomfort.
Mood
Cold, alien and theatrical. Used deliberately it is striking; used accidentally it looks broken.
Sleep & alertness
Maximally disruptive to evening melatonin. Treat as a daytime-or-effect-only source.
Color rendering
CRI is not a meaningful metric this far from a practical white point. Aquarium products are specified on PAR and spectral output instead; stage products on gel or LED color coordinates.
How it feels: Strongly blue, the colour of open shade under a clear sky.
Want to see 10000K in your own room?
The photo tool re-renders a picture of your space at this exact temperature, in your browser.
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