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sean Downsizer Moderator
Joined: 28 Oct 2004 Posts: 42219 Location: North Devon
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jema Downsizer Moderator
Joined: 28 Oct 2004 Posts: 28237 Location: escaped from Swindon
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dougal
Joined: 15 Jan 2005 Posts: 7184 Location: South Kent
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Posted: Wed Feb 09, 05 9:29 pm Post subject: |
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tahir wrote: |
Pure white LED's in 2008 apparently |
Problem is that "pure white", on its own, is not technically meaningful.
The concept of "colour temperature" - Picture a blacksmith heating a horseshoe. Initially its a not glowing - in the range that the eye works in! When it starts glowing, its a dull red. The hotter it gets, the bluer the light given off - it gets "white hot". By measuring the 'colour', the temperature can be measured. Maplin will sell you a "non-contact" thermometer starting at about �20.
Note that the *colder* the source, the subjectively *warmer* the light!
Daylight is from a source at nearly 6000C (I know about K, but please recognise I'm simplifying!) No bulb can possibly run at such a temperature. Take a photograph (on a camera using ordinary colour *film*) by artificial light, and it will be a strange colour. Ordinary bulbs produce something that looks like candlelight!
Note that digital cameras typically try and adjust themselves to the colour of the light. Its because the eye and brain do this so well that we don't think we are living in candlelight!
However all fluorescent lights (inc "energy saving bulbs") don't give out a "continuous spectrum" - they give out a set of specific (pure) colours, which if well spread and carefully balanced give us the impression of 'white-ish' light... but it isn't!
To see what's missing look at a paint colour chart under different lights. The difference between halogen and "energy saving" bulbs is pretty dramatic.
Camera flashguns produce a simulation of daylight, good enough to satisfy ordinary film. Similarly "natural daylight" bulbs produce a simulation of daylight's blue/red balance - but this makes for a seemingly strangely "cold" light...
People doing colour critical work on computer screens not only need to "calibrate" their screens, but also to standardise their room lighting, (and be restrained in their decor), otherwise a 'real' colour that matches the screen colour at midday, will not match in late afternoon, let alone by artificial light in the evening! |
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jema Downsizer Moderator
Joined: 28 Oct 2004 Posts: 28237 Location: escaped from Swindon
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tahir
Joined: 28 Oct 2004 Posts: 45674 Location: Essex
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hardworkinghippy
Joined: 01 Jan 2005 Posts: 1110 Location: Bourrou South West France
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Bernie66
Joined: 14 Jan 2005 Posts: 13967 Location: Eastoft
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tahir
Joined: 28 Oct 2004 Posts: 45674 Location: Essex
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jema Downsizer Moderator
Joined: 28 Oct 2004 Posts: 28237 Location: escaped from Swindon
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hardworkinghippy
Joined: 01 Jan 2005 Posts: 1110 Location: Bourrou South West France
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jema Downsizer Moderator
Joined: 28 Oct 2004 Posts: 28237 Location: escaped from Swindon
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tahir
Joined: 28 Oct 2004 Posts: 45674 Location: Essex
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hardworkinghippy
Joined: 01 Jan 2005 Posts: 1110 Location: Bourrou South West France
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tahir
Joined: 28 Oct 2004 Posts: 45674 Location: Essex
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dpack
Joined: 02 Jul 2005 Posts: 46233 Location: yes
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