Historically with older types of illumination based upon tungsten lamps these light sources reproduced full spectrum of light. Just like the daylight source of light from the sun.
This full spectrum is important as it permits humans to see the colours of items truthfully. So, blues look like blues, reds look like reds, and greens look like greens.
However, under the newer LED light sources, they are unable to provide the full spectrum of light, so the items that you are looking at may not reflect the light, and therefore the colour of the item, back to your eyes truthfully. Colours appear to be off, muddy, or muted. They are not a vivid and crisp as they are under the full spectrum of light.
The human eye is incredibly adaptable and works to correct light deficiencies. So, if you see someone wearing a white blouse, then in your mind’s eye, the blouse does appear to be white. However, since everyone sees slightly differently, then the exact shade of white will vary from person to person. Likewise, if the same person in the white blouse is seen indoors under LED lights and then later seen outdoors under sunlight, the shade of white will change due to the partial versus full spectrum differences of the source light. You may even be fooled to think that she changed her blouse to a different one.
In many industries, this lack of full spectrum lighting is a difficult challenge to overcome.
For example, in the retail industry, when selling expensive clothing, items may look dull and lackluster and not appear to consumers in the same way that the retail buyers expected when they purchased these goods for the stores. Therefore, retailers often spend much more on quality lighting to ensure that the reflected light reproduces the colours faithfully to all consumers. They want their products to look their best, to be attractive, and desired. Muted colours detract from a sale.
In industrial installations of lighting, for emergency exit signs and other important workplace and public venues, the colour of light can have serious safety implications. Certain colours hold different meaning and in critical emergencies these lights can guide people to safety to escape imminent dangers. If partial spectrum lighting is used, the outcomes can mean the difference between life and death.
When broadcasters create programs, it is vital to achieve correct colour renditions in order for the viewers to see consistent colours from scene to scene. For example, if the light sabers in Star Wars changed colours from one scene to the next, the audience would instantly notice this inconsistency. In the Star Wars movies, the colour of the light saber is essential to tell the good guys from the bad guys. But, it goes far beyond the light sabers. What if the characters had greys and greens in their skin colours? Would the heroine, REY be as attractive and relatable to the viewers if she had a sickly grey skin tone? Even your home movies will suffer from the same light rendition challenges under LED lights.
What does full spectrum lighting mean? Light, as we humans see it, is electromagnetic radiation that is visible to the human eye. It is the part of the electromagnetic spectrum we call “visible light”.
The electromagnetic spectrum is the range of all frequencies, or wavelengths, of electromagnetic radiation – from very low energy frequencies like radio waves, to radiation with very high-energy frequencies such as gamma rays.
Sunlight is described as full-spectrum light and includes the range of wavelengths necessary to sustain life on Earth: infrared, visible and ultraviolet (UV).
But the human eye only responds to the visible light component, which lies between infrared and ultraviolet radiation, and emits tiny wavelengths – just 400 to 700 nanometers (nanometer = billionth of a meter).
Visible light includes the spectrum of seven color bands produced when sunlight is refracted through a prism: red, orange, yellow, green, blue, indigo and violet.
For years, ever since the workforce largely migrated from farms to factories, the lighting industry sought to develop electric, artificial light sources that mimicked the properties of sunlight. Since the dawn of mankind, sunlight has governed our daily actions. It tells us when to wake up and when to sleep. We know the time of day and the day of the year all from the quality of sunlight.
Daylight and artificial lights such as tungsten filament bulbs are full spectrum light sources. Though the intensity of light may vary between the red and blue ends of the spectrum produced by these light sources, it is unbroken through the spectrum of colours produced, just like the sub provides to us. However fluorescent and LED light sources produce a discontinuous spectrum consisting of only certain colors. The gaps in the colour spectrums of these light sources cannot be compensated for or corrected with filters or gels. In practical terms, this means that while an artificial light source may, for example, correctly reproduce shades of blue and green in a subject, shades of red may appear different when compared to how they appear in daylight. These partial spectrum light sources are said to be broken.
The International Commission on Illumination (CIE) defines colour rendering as “the effect of an illuminant on the colour appearance of objects by conscious or subconscious comparison with their colour appearance under a reference illuminant”. To enable a meaningful comparison to be drawn between different artificial light sources the CIE created the Color Rendering Index (CRI) in 1964. The CRI score does not represent the color temperature of the light source under test, but the accuracy with which it will reproduce the full range of colours in a subject.
The CRI is calculated by comparing the appearance of a range of sample colours when observed under daylight — or a standardized artificial source — against the light being tested. The results across the sample colours are averaged out to give a single score, with 100 being given to a light which renders colours as accurately as the standardized source. The lower the CRI score, the less accurately a light source will reproduce all colours in a subject. To ensure accurate colour rendition for filmmaking, safety, or retail scenarios, especially with skin tones, a CRI of 90-95 or higher is desirable.
There are some inadequacies with the CRI ratings however. The CRI gives a score for colour rendition as it appears to the naked eye and the imaging sensors in television and video cameras can perceive light very differently. Visually, it is possible to create white light with just a mix of red and blue, but to a camera this would appear very differently. In addition, some of the test colours used to determine CRI were highly saturated and outside the permitted tolerances for broadcast television.
There are other attributes of light that impact our lives, such as colour temperature and brightness. But these topics can be discussed on another post.
Light is how we see and perceive the world around us. All colours are the result of direct or indirect light. Most things that we see are actually the reflection of light off of an object. We can even judge texture from past experiences when we see the colour and quality of light being reflected off of a shiny car, or a warm wool sweater, or the cold, crisp layer of snow in a meadow. We can infer how other senses understand these objects based upon how we see them. We deduce the textures from what we see and previously experienced.
Light is a reality. Darkness is the absence of that reality. Light is a positive force. Darkness is not a force or a presence or a quantity of any kind. It appears only when light disappears. Light is not dependent upon darkness, but darkness is totally dependent upon light. If you knew the meaning of light you would yourself be a light in a dark place.
You may wonder why daylight is relevant to our modern building culture. Consider that human beings live in close relationship to sunlight well into the 20th century. We woke to a reddish sunrise, spent the day in blueish light, with the peak intensity at midday, and fell asleep to the reddish sunset or the warm red glow of firelight. Given centuries of this primordial pattern, it is no coincidence that the shifts in colour during the day regulate our physiology, at all scales, even at cellular levels. Light is vital to life.
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References:
Bair, s. (2012). What is Full Spectrum Lighting? Lumenistics. Retrieved on December 27, 2019 from, https://lumenistics.com/what-is-full-spectrum-lighting/
Tomkies, P. (2019). Understanding CRI & TLCI: The Importance Of Color Rendition. Videomaker. Retrieved on December 17, 2019 from, https://www.videomaker.com/article/c03/18602-understanding-cri-tlci-the-importance-of-color-rendition
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About the Author:
Michael Martin has more than 35 years of experience in systems design for broadband networks, optical fibre, wireless, and digital communications technologies.
He is a business and technology consultant. He is employed by Wirepas Oy from Tampere, Finland as the Director of Business Development. Over the past 15 years with IBM, he has worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin currently serves on the Board of Directors for TeraGo Inc (TGO: TSX) and previously served on the Board of Directors for Avante Logixx Inc. (XX: TSX.V).
He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology.
He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now OntarioTech University] and on the Board of Advisers of five different Colleges in Ontario. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and five certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has earned 15 badges in next generation MOOC continuous education in IoT, Cloud, AI and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, and more.