[opendtv] Re: News: Will LEDs Light Your Productions?
- From: jeroen.stessen@xxxxxxxxxxx
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 22 Oct 2004 08:56:12 +0200
Hello,
LEDs are fantastic for displays, whether they be the pixels
directly, or used as a backlight behind an LCD, or even as the
lamp for a microdisplay (projector). You only need 3 primary
colours to reproduce an image. Just use R+G+B LEDs.
But for lighting a scene for the purpose of filming it with a
camera we have to worry about the spectrum of this LED lighting.
The lighting MUST have a wide and fairly flat spectrum, or else
the colour reproduction will be wrong. So you can not use R+G+B
LEDs, with their narrow spectra, because for example a pure
yellow object would become black... You would have to use white
LEDs then. As white as an incandescent lamp, or as the sun.
White LEDs typically consist of a blue LED die plus a yellow
phosphor on top. If you shine it directly into the eye then
it looks like white light. But the spectrum is not flat enough
to use it for lighting. If it were that easy then all studios
would be lit by fluorescent lamps instead of tungsten (halogen).
They would have to be very careful about the phosphor
composition, to create a lamp with good colour rendition. This
is also done with TL tubes, e.g. for lighting a clothes store,
but then the efficiency drops by 50%. I have some doubts
whether these LED lamps have taken this into consideration...
They might in fact be utterly useless......
Best regards,
-- Jeroen
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| From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx |
| Building: SFJ-5.22 Eindhoven | Philips Digital Systems Laboratories |
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