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History of Light Sources - Color Rendering Index (CRI)

The Pursuit for Quality of Light - Beyond CRI

Since January 2024, Nichia has introduced three blog posts on “History of Light Sources - Color Rendering Index (CRI)” and this blog will conclude its series with this fourth post. In the world of lighting sources, where there is often a tendency to prioritize luminous flux and efficiency, Nichia has strived to convey that CRI is just as important as luminous flux and luminous efficiency. Nichia, which has been involved with “light” for more than half a century since the fluorescent lamp era, hopes that this part of its philosophy has been understood by readers.

Outdoor Lighting and CRI

The first post discussed general lighting and the second one addressed specialty lighting applications requiring a higher CRI. This post will explore outdoor lighting. While it is widely understood why CRI is important for indoor lighting, is it important for outdoor lighting as well? Many people have had the experience of driving into a tunnel and not being able to see clearly, not being able to distinguish car colors directly in front or not even being able to tell the color of fellow passenger’s clothing! This is due to the extremely low CRI of sodium lamps commonly used in tunnel lighting, until recently. As shown by the above example, CRI is also an important factor in outdoor lighting.Despite the widespread adoption of LED lighting, high-pressure sodium lamps (“HPS”) remain the most widely used light source for outdoor lighting such as streetlights, road lights, and landscape lighting. Satellite images of the earth at night show cities around the globe glowing with a beautiful orange color. However, while HPS may look beautiful from the sky, the CRI of HPS is extremely low much like the lighting in tunnels. It is quite difficult to see objects clearly when walking under the illumination of HPS in older towns or container yards, again, sometimes even impossible to distinguish the colors of clothing.

CRI Required for Specialty Lighting

7 February 2024

The first post was about general lighting. In this post, Nichia will discuss specialty lighting which requires a higher CRI.Applications requiring high color rendering include lighting for printing, painting, dyeing, photography, color inspection, cosmetic mirror lighting, galleries, museums, clothing, decorations, hospitals, and schools. Depending on the application, various types of high CRI lamps are used.

The History of General Lighting and CRI

10 January 2024

In the lighting industry, the characteristics and advantages of light sources are typically discussed in terms of luminous flux and/or efficacy; however, CRI, chromaticity, and spectral distributions are also important factors of light. Among these, CRI is a very important characteristic that determines how close an illuminated object looks to what it would like under natural light. In this blog, Nichia has chosen to focus on CRI and its history as the main theme and this first blog post will discuss the importance of general lighting, which is indispensable in our daily lives.

Nichia's contribution to a realization of a mercury-free society

Through technological progress, the world is rapidly heading towards a "mercury-free" society

1 November 2023

In February 2023, Nichia started a blog with the 1st post titled "Nichia's contribution to a realization of a mercury-free society" and for nearly a year, Nichia has been introducing examples of LED/LD replacement for mercury lamps in various fields. Maybe it was surprising to readers to find out that mercury lamps are still used in various applications in modern society. This includes fluorescent lamps, high-pressure sodium lamps (HPS) used in street lights and greenhouse lighting, low-pressure mercury lamps used in disinfection applications, high-pressure mercury short arc lamps in semiconductor photolithography, liquid crystal displays (LCDs) and printed circuit boards (PCBs), medium-pressure mercury lamps used in paint curing and ultra-high-pressure mercury lamps used in projector applications. At the same time, Nichia believes that readers have also realized that new solid-state light sources such as LEDs and LDs are emerging as effective mercury-free alternative technologies.

Alternative Technologies to High-pressure Mercury Short Arc Lamps for Photolithography of Printed Circuit Boards (PCBs)

Photolithography for the manufacture of semiconductors and printed circuit boards (PCBs) is another major application for mercury lamps classified under item 4(f) in the exemption list of the RoHS Directive. This is in addition to curing and photolithography for the manufacture of liquid crystal displays (LCDs), which were described in the previous posts.

Alternative Technologies to High-pressure Mercury Short Arc Lamps for Photolithography Applications

Photolithography for the manufacture of liquid crystal displays (LCDs), semiconductors, and printed circuit boards (PCBs) is another major application for mercury lamps classified under item 4(f) in the exemption list of the RoHS Directive, in addition to curing, which was described in the previous post.

Alternative Technologies to Medium-pressure Mercury Lamps for Paint Curing Applications

Heat and ultraviolet are used to cure paints such as coatings to protect the surface of car bodies, wooden floors, and plastic containers. Medium-pressure mercury lamps are the primary light source for ultraviolet curing (UV curing). Originally, heat and drying were mainly used to cure paints, but after the invention of the mercury lamp, the development of materials that can be cured with ultraviolet increased over time, and curing with ultraviolet became and remains widely used.
Compared to curing with heat, UV curing can be used for heat-sensitive materials and can be done in a shorter time. In addition, since mercury lamps have emission spectra ranging from the UV-C to UV-A region¹ to the visible light region, ultraviolet of various wavelengths can be used for each application. Because of these characteristics, UV curing technology is now being used for semiconductor manufacturing processes, printing, and paints, making ultraviolet and the medium-pressure mercury lamps that irradiate ultraviolet indispensable to those industries.

Alternative Technologies to Ultra-High-Pressure Mercury Lamps for Projector Applications

Projectors are commonly used in meetings and seminars, and their primary light source is still ultra-high-pressure mercury lamps. As the name implies, ultra-high-pressure mercury lamps contain mercury and generate concerns regarding environmental pollution. For that reason, they are expected to be replaced by solid-state light sources which do not contain mercury such as LDs (Laser Diodes) and LEDs. However, due to cost and other reasons, this replacement is taking time, and in the RoHS Directive, ultra-high-pressure mercury lamps for projectors with an output of ≥2,000 lm can be manufactured and sold under an exemption at least until 2027.

Alternative Technologies for the germicidal lamps (low-pressure mercury lamps)

Until today since the discovery of ultraviolet germicidal effectiveness in 1901, primarily low-pressure mercury lamps have been used for disinfection with ultraviolet. Low-pressure mercury lamps contain mercury and therefore generate concerns regarding environmental pollution. LEDs are expected to be an environmentally friendly alternative technology, similar to the LED replacement of fluorescent lamps. However, although improving year over year at a great rate, the current efficiency of UV LEDs is still less than low-pressure mercury lamps. Thus, the RoHS Directive exempts low-pressure mercury lamps for special applications until February 24, 2027 (Item 4(a)) because no alternative technology has been established. After 2027, this exemption could be extended if it is determined that no alternative technology is available. Is an extension really necessary? Nichia believes that LED adoption is immediately possible for some applications and will be possible in nearly all applications well before February 2027.

Alternative Technologies for the High Pressure Sodium lamps (HPS)

Today most fluorescent lamps are regulated by the RoHS Directive. However, despite containing mercury, there are still exemptions. In the field of general illumination, High Pressure Sodium lamps (hereinafter abbreviated as HPS) remain the highest runner of mercury-containing lamps.

Mercury-containing light sources (lamps) exempt from the RoHS Directive

As explained in the February 24, 2023 blog post, there remain lamps and light sources which contain mercury but are still exempt from the RoHS Directive. With its decades of experience and innovation, Nichia wants to contribute to the realization of a mercury-free society by promoting alternative light sources, specifically LEDs and Laser Diodes which do not contain mercury.

The world is heading towards a "mercury-free" society

24 February 2023

As of today, 24 February 2023, most types of fluorescent lamps will be banned from manufacturing and sales in Europe. Despite containing mercury, these lamps have been allowed to be manufactured and sold as exemptions from the RoHS Directive. However, these exemptions end today and will no longer be extended. Lamps not covered this time will be subject to regulation in a phased manner, and general fluorescent lamps, except for some special applications, will disappear from the market in the near future.

30th Anniversary of the High Brightness Blue LED

The Infinite Possibilities of LED Technology

30 November 2023

Since Nichia's invention of white LEDs in 1996, the market for high-brightness LEDs has expanded beyond the applications Nichia had ever expected when first launching blue LEDs. As luminous efficiency of LEDs has improved, the number of applications where LEDs can be used has continued to grow, leading to today's mass adoption.

Blue LED + Phosphor = the Creation of the White LED

11 October 2023

Several years have passed since the launch of blue LEDs, and LEDs have been adopted for the three applications introduced in the previous post (traffic signal/display/scanner). Large screen display systems, which had been used mainly outdoors, have expanded to include large-sized displays used in stadiums to small, high-definition versions for advertising, such as those installed in buildings, and now indoor applications are in sight.

Markets that have been changed by blue LEDs (Traffic Signal/Display/Scanner)

To introduce a completely new technology to the world, it is said that there are three barriers to overcome. They are called the Devil River, Valley of Death, and Darwinian Sea.
There are detailed explanations of each of these terms in specialized literature for business administration and other fields. "The Devil River" is if the development of the product becomes a success. Smooth mass production and commercialization is referenced as "The Valley of Death." Lastly, the formation of the market is known as "The Darwinian Sea". Thanks to the efforts of all involved, Nichia's blue LEDs successfully overcame the Devil River and the Valley of Death. The last challenge was the Darwinian's Sea. Nichia's high brightness blue LEDs were completely new, but the market had already been formed in terms of "LEDs," and Nichia saw the prospect of three market demands that could be obtained by filling in the missing puzzle piece, the "blue" LED.

The Launch of the Blue LED – A Small Announcement That Reached the Whole World

Blue LEDs were ready for mass production, and in November 1993, the day of the launch announcement for the blue LED finally arrived. The announcement was not some gorgeous event like renting out a conference room at a hotel to give a presentation to a large number of media outlets; instead, Nichia just asked the Tokushima branch of the Nihon Keizai Shimbun (Japanese Newspaper company) for an interview. At that time, Nichia Corporation was a completely unknown company to the public. The company was introduced in newspapers, weekly magazines, television, and other media as "the company with the longest summer vacation in Japan¹" once a year. This was how Nichia was known to the public. Also, Nichia was concerned that people would not believe it if Nichia simply announced that Nichia had developed an innovative LED because Nichia was a chemical company with only a few hundred employees in Tokushima which was a rural area at that time.

The march towards mass production of the high brightness blue LED

Rewind the clock 30 years to 1993, red, orange, and yellow-green LEDs were readily mass produced and available in the market. However, although blue LEDs utilizing different substrate materials were available in the market, production quantities were very limited. In fact, these blue LEDs were not as bright as the red and yellow-green LEDs. Therefore, because of the brightness difference between these 3 colors, balance could not be achieved between the three primary colors (red, blue, yellow) necessary to reproduce any color, including white. Various manufacturers and research institutes had been working to develop practical blue LEDs. If you are familiar with the period around the early 1990, you may remember that all LED Departure Boards installed at train stations, for example, were displayed either monochrome (red or orange or yellow-green) or tri-color. Due to the lack of practical blue LEDs, white or full colored displays were not possible. Fast forward 30 years, as the three primary colors of red, green, and blue with balanced brightness are available, more and more departure signs are being displayed in full color.

30th Anniversary of the High Brightness Blue LED

"Blue LED, 100 times brighter"
On November 30, 1993, Nikkei Business Daily headlined the front page of its popular newspaper in Japan – "Blue LED, 100 times brighter." The company that launched such a surprising product is "Nichia Chemical Industries Ltd." (Currently, Nichia Corporation), located in Tokushima, Japan.