Missing Parts Of The Spectrum


Graham Jaggers TV-Bay Magazine
Read ezine online
by Graham Jaggers
Issue 107 - November 2015

Since the phasing out of conventional filament light bulbs and their replacement with fluorescent and LED, many manufacturers indicate the colour accuracy of their lamps with a CRI (Colour Rendering Index) number.

It is possible however, to illuminate a scene using lamps with quite good CRI ratings and experience inaccurate colours on a TV system, despite looking normal to our eyes.

Colour science expert Alan Roberts has developed a different standard for the assessment of lights, which is geared towards illumination for TV cameras. This is becoming the benchmark that manufacturers and TV professionals are turning to in assessing the suitability of a lamp for accurate TV colour rendition. It is known as the Television Lighting Consistency Index (TLCI).

The incandescent light bulb has been with us since the 1840s. Although notoriously inefficient and as good at generating heat as light, it also has some excellent qualities, which have helped it survive so long. One of these is colour. The filament of a light bulb radiates a broad continuous spectrum of light. It is biased towards the red end of the spectrum, but, what we tend to call white tungsten light contains the full spectrum of colours that the human eye can see. Similarly, daylight is biased towards the blue end of the spectrum, but, what we tend to call white daylight contains the full spectrum of colours.

Over millions of years our eyes have evolved into a design that principally utilises red green and blue sensors (cones) that enable us to have good colour vision in daylight conditions.

Colour cameras work to the same concept, utilising red green and blue sensitive sensors to sample the image formed by a lens. Both camera and the human systems rely on the scene being illuminated by full spectrum white light in order to correctly interpret the reflected colours within a scene.

Quite by chance, the filament light bulb has been providing us with camera-friendly illumination that can be colour corrected with a simple white balance, or graded because there is enough colour information in the picture.

Now at last, over a hundred and seventy years after the light bulb was patented, we have a number of more efficient energy saving alternative light sources. Both the motion picture and the domestic home markets are using new generations of fluorescent and LED units to massively cut down on power consumption. Unfortunately, unlike the filament light bulb, these units do not naturally produce a continuous spectrum of visible light. Gas filled fluorescents, and LEDs often have parts of the spectrum missing. (See Fig. 1)
If pictures illuminated with such lamps are compared to continuous spectrum lighting, there is a colour shift. (See Fig. 2)

In the picture each coloured panel and the portrait is a split between a daylight exposure and an LED illuminated exposure. The white balance is correct in both, hence the grey scale matches, but the colours vary widely.

It takes complexity in the manufacture of LEDs and fluorescents to get them good enough for use with TV cameras, so there needs to be a means of assessing and categorising their suitability.

Back in the 1960s the system named the Colour Rendering Index was devised for comparing a light source with an ideal or natural light source. The highest possible value was 100 (full spectrum), which would include incandescent lamps and daylight. Fluorescent lights range from about CRI 50 for the basic types, up to about 90 for the best tri-phosphor type. The CRI was developed for domestic and architectural lighting, intended for direct viewing with the human eye. According to Alan Roberts, its colour samples and mathematics are crude by todays standards and it is not really suitable for use with modern television systems. Some light sources with a high CRI score will still not reproduce accurate colours on TV. However, it is the only colour-difference metric approved by the CIE (the standards body for lighting and colour), so CRI values are commonly displayed for products from domestic compact fluorescent bulbs to sophisticated TV lights.
The Americans made an attempt to improve on the CRI and developed a system named the Colour Quality Scale (CQS), but it was deemed little improvement and it was not adopted.

Alan thought there should be a more meaningful index, suited to TV. He remembered that there had been some work done at the BBC in the 1970s that proposed to mimic an entire television camera/display channel to analyse the performance of a luminaire relative to a reference. This forms the basis of Alans TLCI system. The highest possible value is still 100, but the scale is stretched at the high quality end to give more discerning results and the calculations more accurately represent a camera system. Trials were held where a number of experienced colourists were given sample material to correct. Lamps of different quality and TLCI value illuminated the samples and the colourists reported how difficult the samples were to colour correct. The result confirmed that the TLCI was an improvement over previous systems and that the scale can be related to the potential difficulty of post-production colour-correction. (See Fig. 3)

Many manufacturers are now getting their lamps tested by Alan Roberts and are adopting TLCI values as an improved way to indicate their spectral quality. Those of us using lamps professionally should be grateful for the determined effort he has made to develop a system that will help us select lamps of appropriate quality for the job.

Tags: iss107 | lighting | spectrum | colour | filament light bulbs | LED | colour science | Graham Jaggers
Contributing Author Graham Jaggers

Read this article in the tv-bay digital magazine
Article Copyright tv-bay limited. All trademarks recognised.
Reproduction of the content strictly prohibited without written consent.

Related Interviews
  • Area 48 Colour from BBandS Lighting plus more announcements at NAB 2019

    Area 48 Colour from BBandS Lighting plus more announcements at NAB 2019

  • Hive Lighting at IBC 2015

    Hive Lighting at IBC 2015

  • FilmGear LED lighting at IBC 2015

    FilmGear LED lighting at IBC 2015

  • DoP Choice show the latest lighting solutions at NAB 2019

    DoP Choice show the latest lighting solutions at NAB 2019

  • Area 48 Color and more from BBS Lighting at IBC 2018

    Area 48 Color and more from BBS Lighting at IBC 2018

  • BBS Lighting Force 7 at NAB 2018

    BBS Lighting Force 7 at NAB 2018

  • DOP Choice Lighting Bracket and Snapbox at IBC 2017

    DOP Choice Lighting Bracket and Snapbox at IBC 2017

  • LSC Lighting at IBC 2015

    LSC Lighting at IBC 2015

  • LCA - Snapgrid lighting control - BVE 2015

    LCA - Snapgrid lighting control - BVE 2015

  • Hive Lighting Wasp Plasma Par at IBC 2014

    Hive Lighting Wasp Plasma Par at IBC 2014

  • Lighting cameraman Jonathan Harrison shows the Celeb and Tegra at IBC 2013

    Lighting cameraman Jonathan Harrison shows the Celeb and Tegra at IBC 2013

  • LiteGear LED LiteMat at IBC 2015

    LiteGear LED LiteMat at IBC 2015

  • Zylight LED Fresnel at IBC 2013

    Zylight LED Fresnel at IBC 2013

  • Dedolight Felloni Turbo and Felloni 3 shown at BVE 2018

    Dedolight Felloni Turbo and Felloni 3 shown at BVE 2018

  • Rotolight Anova Pro 2 shown at BVE 2018

    Rotolight Anova Pro 2 shown at BVE 2018

  • KitPlus filming rig used at NAB 2017

    KitPlus filming rig used at NAB 2017

  • Cirrolite and Kino Flo at BVE 2017

    Cirrolite and Kino Flo at BVE 2017

  • Cineo HS2 at IBC 2015

    Cineo HS2 at IBC 2015

  • LiteGear at IBC 2015

    LiteGear at IBC 2015

  • Cineo Matchbox at IBC 2015

    Cineo Matchbox at IBC 2015

  • Litepanels at BVE 2015

    Litepanels at BVE 2015

  • LCA - LITEGEAR at BVE 2015

    LCA - LITEGEAR at BVE 2015

  • Rosco at BVE 2015

    Rosco at BVE 2015

  • Photon Beard Platinum Blonde at IBC 2014

    Photon Beard Platinum Blonde at IBC 2014

  • Photon Beard Photon Beam at IBC 2014

    Photon Beard Photon Beam at IBC 2014

  • Zylight Fresnel updates at IBC 2014

    Zylight Fresnel updates at IBC 2014

  • Photon Beard on BroadcastShow LIVE at IBC 2013

    Photon Beard on BroadcastShow LIVE at IBC 2013

  • AC Entertainment Technologies at BVE 2013

    AC Entertainment Technologies at BVE 2013

  • Litepanels at BVE 2012

    Litepanels at BVE 2012

  • Jonathan Harrison at BVE North 2011

    Jonathan Harrison at BVE North 2011

  • Litepanels at IBC2011

    Litepanels at IBC2011

  • Gekko at IBC2011

    Gekko at IBC2011

  • Photon Beard at IBC 2016

    Photon Beard at IBC 2016

  • Projects Department on BroadcastShow LIVE at IBC

    Projects Department on BroadcastShow LIVE at IBC

  • Ianiro on BroadcastShow Tour May 2013

    Ianiro on BroadcastShow Tour May 2013

  • Photon Beard: Cyc Hood at NAB 2013

    Photon Beard: Cyc Hood at NAB 2013

  • Photon Beard: Space Light at NAB 2013

    Photon Beard: Space Light at NAB 2013

  • Photon Beard: Square One Light at NAB 2013

    Photon Beard: Square One Light at NAB 2013

  • Jonathan Harrison at BVE North 2012

    Jonathan Harrison at BVE North 2012

  • Rotolight at NAB 2012

    Rotolight at NAB 2012

  • Litepanels at NAB 2012

    Litepanels at NAB 2012

  • Rotolight and TNP at BVE 2012

    Rotolight and TNP at BVE 2012

  • Datavision at BVE 2012

    Datavision at BVE 2012

  • Rotolight at ProVideo2011

    Rotolight at ProVideo2011

  • Flaghead Photographic at ProVideo2011

    Flaghead Photographic at ProVideo2011

  • Cirrolite at BVE North 2011

    Cirrolite at BVE North 2011

  • PAG at IBC2011

    PAG at IBC2011

  • Photon Beard at IBC2011

    Photon Beard at IBC2011

  • IDX at IBC2011

    IDX at IBC2011

  • Schneider Optics showing the first full spectrum neutral density grad filter at NAB 2019

    Schneider Optics showing the first full spectrum neutral density grad filter at NAB 2019

  • Full Spectrum Remote Phosphor Lights from Photon Beard at NAB 2018

    Full Spectrum Remote Phosphor Lights from Photon Beard at NAB 2018

  • Shure Sound Devices at BVE 2013

    Shure Sound Devices at BVE 2013

  • Shure Axient at BVE 2013

    Shure Axient at BVE 2013

  • Quantel Pablo Rio at NAB 2013

    Quantel Pablo Rio at NAB 2013

  • SGO at IBC2011

    SGO at IBC2011

  • Telestream Vantage Powerful, Scalable, Software-Enabled Media Processing Platform at BVE 2019

    Telestream Vantage Powerful, Scalable, Software-Enabled Media Processing Platform at BVE 2019

  • Dedolight DLED3 shown at IBC 2018

    Dedolight DLED3 shown at IBC 2018

  • Dedolight show the LED Raptor Bicolor at IBC 2018

    Dedolight show the LED Raptor Bicolor at IBC 2018

  • Rotolight Anova Pro 2 LED at NAB 2018

    Rotolight Anova Pro 2 LED at NAB 2018

  • Jonathan Harrison interviews Dedo Weigert with the DEDOLIGHT DLED3

    Jonathan Harrison interviews Dedo Weigert with the DEDOLIGHT DLED3

  • Force 7 LED LEKO light from BBS at IBC 2017

    Force 7 LED LEKO light from BBS at IBC 2017

  • Kino Flo Celeb 850 and Freestyle LED lights at IBC 2017

    Kino Flo Celeb 850 and Freestyle LED lights at IBC 2017

  • PhotonBeard - LED Redhead - at BVE 2015

    PhotonBeard - LED Redhead - at BVE 2015

  • Zylight F8 LED Fresnel at NAB 2013

    Zylight F8 LED Fresnel at NAB 2013

  • SmallHD shows the Cine 7 monitor with camera control and integrated Teradek Bolt at NAB 2019

    SmallHD shows the Cine 7 monitor with camera control and integrated Teradek Bolt at NAB 2019

  • KitPlus filming rig used at BVE 2017

    KitPlus filming rig used at BVE 2017

  • Filming kit review from NAB

    Filming kit review from NAB

  • Kino Flo at NAB 2016

    Kino Flo at NAB 2016

  • Dedolight at NAB 2016

    Dedolight at NAB 2016

  • Photon Beard at IBC 2015

    Photon Beard at IBC 2015

  • Zylight at IBC 2015

    Zylight at IBC 2015

  • Dedolight at IBC 2015

    Dedolight at IBC 2015

  • Kino Flo Select at IBC 2015

    Kino Flo Select at IBC 2015

  • LCA - Inteca products at BVE 2015

    LCA - Inteca products at BVE 2015

  • Zylight on BroadcastShow LIVE at IBC 2013

    Zylight on BroadcastShow LIVE at IBC 2013

  • Sonifex at BVE 2012

    Sonifex at BVE 2012

  • Pixelution at BVE North 2011

    Pixelution at BVE North 2011


Related Shows
  • LED Lighting with Den Lennie at BVE

    LED Lighting with Den Lennie at BVE


Articles
The World of 12G 4K/UHD Processing
Varun Patel Technology moves fast and when it comes to audio and video broadcasting, there is always room for improvements in audio and video quality and ease of production. One of the main goals of broadcasters and content providers today is to create an immersive experience for the viewers, giving them the feeling of being part of the viewed content. The 4K/UHD buzz has been in the consumer world for some time but what does that actually mean for the content producer?
Tags: iss138 | lynx technik | ott | greenmachine | yellobrik | conversion | Varun Patel
Contributing Author Varun Patel Click to read or download PDF
How LiveU Has Changed The Way We Work At ITV Daytime
Tim Guilder As my job title suggests, I’m responsible for planning and executing technology projects across ITV’s Daytime, including outside broadcasts, which are central to what we do. We broadcast live for more than six hours every weekday with four shows: Good Morning Britain, This Morning, Lorraine and Loose Women. With a history as one of the main UK terrestrial broadcasters – of course, we have also evolved alongside the industry in terms of viewing options – we have high standards. We constantly generate new ideas to keep audiences engaged and we also need to be responsive to the latest breaking news.
Tags: iss138 | liveu | itv | daytime | cobham | explorer 8100 | satellite | lu600 hevc | ka-band | lu300 | garland | Tim Guilder
Contributing Author Tim Guilder Click to read or download PDF
Industry Ready Broadcasting Students
KitPlus Cardiff Metropolitan University traces its roots back to 1865, when they opened their first school in an old library. Now Cardiff Met is a global, practice-focused and professionally oriented institution, committed to ensure every student fulfills their potential to make outstanding contributions in their future industries.
Tags: iss138 | newtek | live production | cardiff metropolitain | sports broadcasting | tricaster | cardiff devils | KitPlus
Contributing Author KitPlus Click to read or download PDF
Centre Stage for Cameras with All About Eve
Anthony Newton Taking its inspiration from the classic 1950 film, Ivo van Hove’s stage production of All About Eve, starring Gillian Anderson as theatre darling, Margo Channing, and Lily James as the eponymous Eve, retains the themes of ageing, celebrity and obsession. The piece, produced by Sonia Friedman Productions and Fox Stage Productions garnered stellar reviews during its recent run at London’s Noel Coward Theatre.
Tags: iss138 | blackmagic design | micro studio camera | ronin | smartscope duo | Anthony Newton
Contributing Author Anthony Newton Click to read or download PDF
Making a Difference in Wireless Transmission
Lukasz Malankowski

We are very proud to say that we are the only company that provides a highly specific service, and that is the hire of wireless video transmission solutions operating in the licence exempt spectrum.

There are other companies that provide licensed equipment and offer a diverse range of wireless solutions based on different modulations, but our products, coupled with the offerings of others rather than competing with them produce a wireless workflow that is greater than their separate capabilities.

Tags: iss138 | boxx | production | wireless | 4k | Lukasz Malankowski
Contributing Author Lukasz Malankowski Click to read or download PDF