Resources | LpR Article | Light Generation | LEDs | Human Centric Lighting | Jul 02, 2018

A Near Infrared Enhanced LED Lighting Approach

With the evolution of LED lighting, one topic has come more and more in the focus of the lighting industry: Human Centric Lighting (HCL). While HCL is not clearly defined, a common understanding is that this is light and lighting that supports health and the well-being of humans. Some new proposals are going beyond the approach of providing just visible light in adequate quality, but also to providing invisible radiation, UV and/or NIR that support health and well-being. Some research and the evolution of humans show clear evidence for positive effects of this kind of illumination. Scott Zimmerman, CEO at Silas, presents a new approach that adds NIR radiation to LED illumination. He explains the background of this idea, how it also improves the quality of visible light and discusses the health benefits.

For millions of years the sun has provided approximately 90% of its energy in Near Infrared (NIR) and Visible (VIS) wavelengths with the remaining percentage being roughly divided between ultraviolet (UV) and mid/long infrared (IR).

In a very short evolutionary time frame (200 years) we have moved from a predominately agrarian society where we spent 90% of our time in the sun to the present where we spend 90% of our time under artificial lighting (EPA estimate). In that same time frame, ethnic groups have migrated from their evolutionary regions. This raises several key issues associated with what is the optimum HCL baseline or even if there is just one HCL baseline for everyone.

As shown in Figure 1, the lighting community is in the process of radically narrowing the spectral range of our artificial lighting environment compared to what our cells have evolved under. This change has been driven by cost, technology, and energy savings but appears to not be supported by any health or wellness benefits.

Figure 1: The lighting community is in the process of radically narrowing the spectral range of our artificial lighting environment compared to what our cells have evolved under (Credits: Nick Spiker, 1: The lighting community is in the process of radically narrowing the spectral range of our artificial lighting environment compared to what our cells have evolved under (Credits: Nick Spiker,

What HCL Baseline Should We Use?

This spectral reduction started 150 years ago with filament sources which provided copious amounts of NIR/IR but very little UV/blue content needed for melatonin stimulation. Fortunately, through most of this timeframe we were a substantially agrarian society with significant time in the sun. Over the last 40 years we have begun to shift to “Just Visible” (JV) lighting via fluorescent but with still significant NIR/IR from incandescent light sources in our homes. In the last 10 years we have begun a process that eliminates virtually all NIR/IR sources from our artificial lighting environment. This unfortunately coincides with energy saving NIR reflecting window treatments and skin cancer concerns reducing our time outdoors. As shown by the UV/VIS/NIR/IR pictures our bodies absorb and react very differently to each spectral region.


UV spectral regions provide energy for Vitamin D production. On the other hand, highly energetic UV radiation UV can harm our tissues, destroy our genetic information, and cause cancer. Melanin is the dominate absorber providing protection against UV ionizing radiation and its associated skin cancer. - Fair skinned individuals with low melanin levels are 10 times more likely to develop skin cancer than dark skinned individuals.


Our visual system is limited to a range between about a little below 400 nm up to around 700 nm. This visible radiation is commonly called light, and the lighting industry is mostly focusing on it. This is characterized by the trend to offer light sources that only provide this “just visible spectrum” (JV lights). This radiation range, especially the highly energetic blue range, is also relevant for our photopic circadian cues. The blue range also affects our physiology and it may cause some damage in tissues.


The majority of the energy from the sun our bodies absorb is in the NIR. In this spectral region, melanin levels are dropping logarithmically allowing for penetration depths in excess of 1 inch into our body even through our skulls. Most organic materials (leaves, fabrics, and colorants) are essentially transparent as shown in Figure 2 (Nick Spiker).

Figure 2: The pictures demonstrate the differences in absorption and reflection of visible (VIS) radiation (left) and near infrared (NIR) radiation (right). - For comparison reasons the images are held in gray scalesFigure 2: The pictures demonstrate the differences in absorption and reflection of visible (VIS) radiation (left) and near infrared (NIR) radiation (right). - For comparison reasons the images are held in gray scales


About 8% of the energy from the sun falls in the IR spectral region. This region is dominated by water absorption as melanin absorption approaches zero. In the IR we are all created equal (dark skin and white hair). While controversial and beyond the scope of this article, there is even evidence that both NIR and IR are fundamental to energy storage in the body.

About the definition of light

While light is strictly defined as those wavelengths to which our eyes respond, in the author’s opinion this definition is in part responsible for us missing the importance of UV/NIR/IR to our cells and HCL. For the purpose of this paper light will be used to refer to UV/VIS/NIR/IR radiation.

Proposed HCL Baseline

Three basic tenets are proposed for the HCL baseline:
•    Minimum NIR/VIS ratio of greater than 1
•    Zero flicker
•    Lighting should adapt to skin pigmentation levels

In general, the common sense argument is that nature is opportunistic and that over millions of years our cells have evolved to take advantage of the 60% of the spectral energy our eyes don’t see. This argument is further justified by daylighting studies [1] indicating that sunlight is always superior both short term and long term to our existing artificial lights. Even further, the medical community is publishing over 400 peer reviewed papers per year on NIR treatments [2, 3, 4]. Ironically, at the same time, the lighting community is eliminating a major source of NIR/IR from our lives, the medical community is discovering that NIR can be used to treat everything from dementia to wrinkles. Sports teams are even using NIR treatments to increase athletic performance [5] with concern that its use should be banned from competitive sports [6]. In some ways the lighting and medical communities seem to be headed in opposite directions.

The three basic tenets are derived from three observations.

The NIR/VIS ratio

All natural light sources have NIR/VIS ratios greater than 1: The NIR/VIS ratio for the sun ranges from 1 (midday) to 5 (sunrise/sunset), moonlight is around 2 and fire ranges from 5 to 10. 1000s of medical articles indicate that NIR functions to protect and repair our cells via stimulation of ATP production in our mitochondria [7]. There also exists new water research [8] which indicates NIR/IR may be fundamental to energy storage at a cellular level. Interestingly, there exists between 700 and 1000 nm a biological window [9] in which absorption is at a minimum. This allows NIR to penetrate over an inch into our bodies even through our skull. The majority of our cells only “see” NIR wavelengths. NIR is, for example, strongly absorbed by our blood but very weakly absorbed by the other surrounding tissue making the blood vessel visible in the NIR not apparent in the VIS. Also sclera transmission and absorption varies depending on the spectral range (Figure 3).

Figure 3: The UV, VIS, NIR pictures show the differences in eye absorption. Figure 3: The UV, VIS, NIR pictures show the differences in eye absorption. The sclera (white of the eye) strongly reflects VIS light but is 4 times more transmissive to NIR Credits: Nick Spiker, - For comparison reasons the images are unified to gray scales

About flicker

Flicker is harmful and may even be a factor in rising dementia rates. While probably the most controversial tenet, flicker does not occur in nature and only exists to simplify drive electronics. Recent work at MIT indicates that pulsed light impacts plaque formation as it relates to dementia [11]. It is also generally accepted that a significant percentage of the ASD population is sensitive to flicker [12].

Light and skin pigmentation

Prior to recent migrations, skin pigmentation evolved solely based on latitude and foliage conditions. As shown in Figure 4, this evolutionary adaptation leads to huge differences in how NIR light is absorbed in the human body. It is doubtful that a single optimum HCL baseline exists for all ethnic groups and, in fact, it could be argued that certain ethnic groups are being disadvantaged by our JV lighting approach. Given that we are latitude mobile, it would appear that an optimum HCL baseline needs to adapt to the skin pigmentation of the individual.

Figure 4: Lambda Research TracePro model of the differences how NIR light is absorbed in the human body. NIR uniquely penetrates over an inch into our body (even our skull) reducing inflammation, enhancing cognitive skills, and stimulating muscle strengthFigure 4: Lambda Research TracePro model of the differences how NIR light is absorbed in the human body. NIR uniquely penetrates over an inch into our body (even our skull) reducing inflammation, enhancing cognitive skills, and stimulating muscle strength

Coincidence or Critical Issue?

African Americans have the highest dementia death rate (80/100,000) in the world nearly twice that of their white American counterparts [13]. This is contrasted with black populations at the equator having some of the lowest dementia death rates (1/100,000) [14]. 90% of lighting in the Soviet bloc until recently was incandescent “Ilyvich” bulbs unlike the US and Europe. Dementia death rates in Russia are (2/100,000) while Finland dementia death rates are (53/100,000) [14]. Myopia rates are skyrocketing especially in Asian countries which predominately use JV LED lighting [15]. Horticulture lighting is adding NIR to enhance growth rates [16]. Non VIS circadian cues are being proposed [17]. Macular degeneration is being treated with NIR [18].

While the exact root causes for above are unknown, it is reasonable to think that lighting plays some role. Why is it so hard to establish a HCL baseline?

Need for HCL Baseline Studies

Unlike plants, it is difficult to accurately assess the impact of light on humans as we move around and live a wide range of lifestyles. Given that natural sunlight delivers up to 60 MJ/day of UV/VIS/NIR/IR onto a typical human body and that an incandescent lamp can locally deliver even higher NIR exposure levels when we sit down to read a book, simple variations in lifestyle can significantly impact light exposure studies. In general, there is a lack of long term research which takes into account the total light exposure of the participants on a daily, weekly, and monthly basis. Added to this lack of controlled studies, the medical community is motivated to develop treatments which can be done within the time constraints of an office visit, while the lighting community is motivated to limit the spectral range as much as possible to save energy. Neither of those two motivations are helpful in determining what the optimum HCL baseline should be.

Proposed Solution – Measure and Simplify Lighting

The proposed solution consists of two parts
•    Daily, weekly, monthly UV/VIS/NIR exposures levels tracking
•    Adopt NIR enhanced LED lighting that mimics the complete circadian spectrum without the need for complex drivers

Light exposure tracking

An app can accumulate daily, weekly, and monthly exposure data based on the location, time of day, and weather conditions. While an estimate, there exists a wealth of information that can be accessed from a mobile device. This combined with some individual responses regarding; does your office have LED or fluorescent lighting, do the windows have NIR reflecting coatings, what are you wearing (e.g NIR transmitting clothing), etc. can be used to further refine the accuracy of the monitoring. With the introduction of NIR cameras in cellphones it is now possible to directly measure UV/VIS/NIR levels and input the data into the app. In general, the purpose of the app is to expand the spectral range we “see”, so we can make appropriate lifestyle changes.

NIR enhanced LED lighting

Figure 5 depicts a NIR enhanced LED lighting source that mimics both the intensity and spectral shifts of the sun (Complete Spectrum Circadian™) simply by adjusting the input voltage. The system can be scaled to any lumen level and the ratio of NIR/VIS can be adjusted for individual preference or skin pigmentation levels.

Figure 5: NIR enhanced LED lighting source that mimics both the intensity and spectral shifts of the sunFigure 5: NIR enhanced LED lighting source that mimics both the intensity and spectral shifts of the sun

The system is based three components; a novel CNT Yarn LED package and 2 wire terminal filament sources. The filament sources are non-linear resistors used to eliminate the need for complex constant current drivers as shown in Figure 6.

Figure 6: U/I diagrams for an LED, an Incandescent and a combined light sourceFigure 6: U/I diagrams for an LED, an Incandescent and a combined light source

Low temperature filament sources are the longest living man-made light source known (Century bulb) and are 90% efficient at generating NIR/IR light. From room temperature to operating temperature a filament source increases its resistance tenfold. A patent pending series/parallel design is used to create the spectral and intensity IV response which mimics the sun simply by adjusting the voltage from zero to peak voltage (0-15 V in the example from figure 5). This eliminates the need for constant current drivers and flicker associated with PWM dimming methods. The technique can be used for both DC and AC inputs and scaled to any lumen output level. However based on the previous flicker discussion it is proposed that this solution should be used as a catalyst to push DC lighting solutions.

The author is keenly aware of the heresy associated with bringing filament sources back into lighting. While the use of current limiting resistors with LEDs are common place, the idea that a couple of grain of rice filament sources could be used with an LED to eliminate complex drive electronics and provide beneficial NIR/IR light is somehow taken as a step backwards.

While the IP covers a host of means of creating NIR enhanced LED lighting including NIR phosphors, NIR LEDs/LD/VCSELs, and quantum dot converters, this filament configuration is the most efficient, cheapest, greenest, longest life expectancy, broadband, and the simplest HCL solution. The life expectancy of small filament sources exceeds 300,000 hours when they are not required to generate significant blue/green light. They do however provide significant orange and red even at these low drive levels to the benefit of color quality while they generate copious amounts of NIR. By combining two competitive technologies both technologies benefit.

The majority of the resistance change in filament sources occurs at lower drive levels. By matching the filament resistance curves with the LED IV curves it is possible to eliminate the need for constant current drivers. Given that the filament sources are 90% efficient at generating NIR most of the energy consumed is used by the LEDs (only 40% to 50% efficient) at peak drive levels depending on what NIR/VIS ratio is selected. Using this approach, 80 to 100 lm/W source efficiencies are possible with NIR/VIS greater than 1. The reduced raw material costs, health benefits, higher reliability, and cost savings associated with simpler drive electronics offset any energy penalty incurred by adding NIR back into our lives.

As stated earlier the filament sources are 90% efficient and have longer life expectancy than the LEDs. At these low drive levels the only significant thermal load on the LEDs from the filament sources is via radiation coupling which represent only a fraction of the light emitted by the filament and can be easily minimized via placement or shrouding. Unlike incandescent and halogen sources of the past, the function of the filament sources in these design are only required to match the VIS optical watts outputted by the LEDs. At 90% efficiency a small T1 filament bulb run at 80% drive level can output more NIR optical watts than the VIS optical watts generated by a 300 lumen JV LED bulb.

To improve the LED reliability, a novel interconnect method was developed. Using CNT Yarns a dual sided CSP emitter can be formed. Unlike conventional solder based connections, the gold/CNT contacts are glued together using a high temperature rigid silicone rated to 600°C. CNT Yarns are inherently “sticky” due to the large surface area created by millions of fibers making up the yarns. In this design the CNT Yarn serves as both the electrical and thermal conductors. Two Seoul Semiconductor CSP die are bonded back to back as shown in Figure 7.

Figure 7: Structure of the proposed LED+Filament light sourceFigure 7: Structure of the proposed LED+Filament light source

By using CNT Yarn instead of metal wire and solder, failures associated with electromigration are eliminated and a wide range of mounting configurations can be used. Typically filament sources and CNT Yarn LED packages are simply crimped or tied together. Additional cooling surface area can be attached as needed. The lumen output can be scaled either by using additional groups or by using high wattage components. In both cases, peak drive levels on the filaments are maintained at low levels such that the product lifetime is defined by the LEDs not the filaments. This design approach uses the minimum raw materials possible, contains no red listed materials, and is compatible with cradle to cradle.

NIR Enhanced LED Lighting offers a practical, common sense solution that complements all daylighting efforts. We have a very limited knowledge of how light interacts with our cells, but the deeper we look the more we find that light plays a significant role in our health. Lighting should follow the medical community’s lead and adopt a “first do no harm” philosophy. As the data from the app becomes available we may be able to limit the spectrum for some individuals. Until that time the daylighting studies and medical research would seem to indicate that we should mandate that all artificial lighting we are spending significant time under have a minimum NIR/VIS ratio of greater than 1.


For millions of years our cells have received a specific spectral and temporal exposure. It is naïve to think that nature has not developed mechanisms that take advantage of this exposure and recent medical data appears to support this position. For the last 150 years we have been removing spectral content from our lighting. Recent government action, lifestyle changes, skin cancer concerns, and the blind pursuit of energy savings will eliminate over 70% of the solar spectrum from our lives over the next decade. There appears however to be no data which supports reducing the spectral range yet numerous indications to the contrary. The medical community appears to be headed in the opposite direction of the lighting community showing the NIR/IR light benefits the body and can even be used to treat ailments using energy exposure levels similar to those possible in lighting systems. There exist practical, energy efficient, and lower cost solutions that don’t require us to compromise. At this point, standards and government programs represent the most significant hurdle to HCL. It is proposed that the NIR enhanced LED Lighting is consistent with daylighting efforts in the architectural community and should be mandated for areas in which there is long term exposure.




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