[opendtv] Re: News: Will LEDs Light Your Productions?
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 25 Oct 2004 15:39:49 +0100
Jeroen,
I meant that the method of producing the initial energy is the same as in a
normal fluorescent, there's nothing special about it. Any means of producing
UV will do. And I never mentioned efficiency. only suitability for use in
film/tv lighting, because the relatively smooth spectral distribution they
produce are fine for colour rendering situations.
By the way, you CAN'T make a perfectly good tv display with monochromatic
emitters. It'll be fin for 85% or males and 93% of females, but for the
remainder, those with abnormal colour vision, they'll get very poor display
of colour. Phosphors with wide-spread spectral energy are far better,
satisfying nearer 99% of the population.
But you're right about the use of scenic illuminants with only a few
spectral lines, they're totally useless for colour analysis, that's why
tungsten filaments are still popular, and why discharge lamps have phosphor
re-emitters to get broader spectral distribution. Spiky spectra with few
lines and low background emission are rubbish for colour analysis.
The spectral distribution of the illuminant does not have to be smooth, as
long as the spikes do not dominate. I measured many fluorescents years ago
when they were being introduced for tv use, the Videssence tubes were
remarkably good, producing an almost exact P3100 chromaticity. Kino-flow
tubes are even better, simulating daylight or thereabouts as well as P3100.
I don't need to convince you of this, just look at any tv or film
production, you'll fins fluorescents in wide use, have been for years. Like
I said, there's no magic about this.
And I'm just fine with the theory, I've been investigating and using it for
25 years, and make a reasonable living in teaching it to others. I've been
trying to teach it to you for some years now, but I don't seem to be having
much success :-)
----- Original Message -----
From: <jeroen.stessen@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Monday, October 25, 2004 11:56 AM
Subject: [opendtv] Re: News: Will LEDs Light Your Productions?
>
>
>
>
> 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:
>
>
http://www.prismaecat.lighting.philips.com/LightSite/Whirlwind.aspx?eca=LEPPLG&cpf=NLEPNL&stg=ACT&lan=NL+&ecu=LMP|PHL|EP&cnt_key=TLD9GRAP|PHL&t=1&tree=0&scr_md=1111&leftnav=1_1_1_5_2_7
> (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 |
> | Phone: ++31.40.2732739 | Visiting & mail address: Glaslaan 2 |
> | Mobile: ++31.6.44680021 | NL 5616 LW Eindhoven, the Netherlands |
> | Pager: ++31.6.65133818 | Website: http://www.pdsl.philips.com/ |
> +-------------------------------+----------------------------------------+
>
>
> 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
>
> Application
> Used in applications where excellent colour rendering is crucial,
> such as the graphical industry, printing industry, photo shops,
> hospitals, etc.
>
> System
> Can be used with conventional or HF electronic gear
>
>
>
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