[opendtv] Re: News: Will LEDs Light Your Productions?

  • From: jeroen.stessen@xxxxxxxxxxx
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 25 Oct 2004 12:56:48 +0200

Dear Alan,

You wrote:
> Fluorescent lamps for tv use are normal discharge lamps that have
> phosphor coatings.

I hope that they are not too normal, because normal home/office
fluorescent lamps have an inferior colour spectrum. But we make
special lamps for a.o. the graphics industry, like the TL-D 90:

 (see below).

> Judicious mixtures of phosphors can produce a really good white
> that works extremely well for tv. That's how Videssence
> and Kinoflow work.

That's the point: it is a special phosphor mixture, optimized for
colour rendering. It is NOT also optimized for high efficiency.
For high-efficiency use the standard lamps, e.g. TL-D 80.

> It's also how tv crts work, three phosphors emit coloured light when
> illuminated with high-velocity electrons. The ad-mixture reproduces any
> colour within the gamut of the chromaticities of the three phosphors.

That is totally uncomparable ! You could make a perfectly
good TV with 3 monochromatic phosphors, LEDs, lasers, etc.
It takes only a linear 3x3 matrix to correct it to R.709
colorimetry. But if you had some "white" lamp with only 2 or
3 spectral lines to illuminate a scene, then no matrix in the
world can correct that signal back to a R.709 standard signal.
In fact, the human eyes that are present on the scene will
also see the wrong colours. It's a bad lamp in any case...

At least with a bad lamp and a good camera, the TV viewers
will see approximately the same bad picture as the studio
audience. With a good lamp and a bad camera (with the wrong
colour filters that can not be corrected by a 3x3 matrix)
it is only the TV viewers that suffer. But with a bad lamp
and a bad camera, all bets are off.

I would hesitate before I applied LED or fluorescent lamps
which have not been designed specifically for good colour
rendering, i.e. with an almost flat spectrum without major
gaps. Convince me otherwise...

> This is standard colour science, there's no magic.

You might want to brush up a bit on the theory...

Best regards,
-- Jeroen

| From:     Jeroen H. Stessen   | E-mail:  Jeroen.Stessen@xxxxxxxxxxx    |
| Building: SFJ-5.22 Eindhoven  | Philips Digital Systems Laboratories   |
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TL-D 90 Graphica Pro

Product Description
      Low-pressure mercury discharge lamps with a tubular 26 mm envelope

Product Features
      High-quality fluorescent coating
      Available in two colour designations

Product Benefits
      Excellent colour rendering. Making representation of colours
      extremely realistic. (Pro range: high quality light!)
      Lamp developed to answer the needs of the demanding graphical
      industry (consistent with ISO 3664:2000, norm for viewing conditions
      in grahical industry)
      Very accurate color point
      Attractive packaging configuration
      Direct retrofit for all Standard and Super /80 TL-D lamps operating
      on conventional or HF gear
      Choice of daylight and cool daylight colours

      Used in applications where excellent colour rendering is crucial,
      such as the graphical industry, printing industry, photo shops,
      hospitals, etc.

      Can be used with conventional or HF electronic gear

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