# Solid-State Lighting: Health Effects and Knowledge Gaps

Christophe Martinsons, Jennifer A Veitch, Sarah Loughran, Ashley Nixon, Rohan Mate, Rachael Harris, Linda Shen

► To cite this version:

Christophe Martinsons, Jennifer A Veitch, Sarah Loughran, Ashley Nixon, Rohan Mate, et al. Solid-State Lighting: Health Effects and Knowledge Gaps. 2024 IEEE Sustainable Smart Lighting World Conference (LS24), Eindhoven Technical University, Nov 2024, Eindhoven, France. pp.1-4, 10.1109/LS2463127.2024.10881837. hal-04957516

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Submitted on 19 Feb 2025

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# Solid-State Lighting: Health Effects and Knowledge Gaps

Christophe Martinsons
*Centre Scientifique et Technique du Bâtiment*
Saint Martin d'Hères, France
Christophe.Martinsons@cstb.fr

Jennifer A. Veitch
*NRC Construction*
National Research Council Canada
Ottawa, Canada
Jennifer.Veitch@nrc-cnrc.gc.ca

Sarah Loughran
*Australian Radiation Protection and Nuclear Safety Agency*
Melbourne, Australia
Sarah.Loughran@arpansa.gov.au

Ashley Nixon
*NRC Construction*
National Research Council Canada
Ottawa, Canada
Ashley.Nixon@nrc-cnrc.gc.ca

Rohan Mate
*Australian Radiation Protection and Nuclear Safety Agency*
Melbourne, Australia
Rohan.Mate@arpansa.gov.au

Rachael Harris
*Monash University*
Melbourne, Australia
Rachael.Harris1@monash.edu

Linda Shen
*Monash University*
Melbourne, Australia
Lindashen93@gmail.com

Authors' version of:
C. Martinsons et al., "Solid-State Lighting: Health Effects and Knowledge Gaps," 2024 IEEE Sustainable Smart Lighting World Conference & Expo (LS24), Eindhoven, Netherlands, 2024, pp. 1-4, doi: 10.1109/LS2463127.2024.10881837. Published 18 Feb 2025 by IEEE

**Abstract**— The health effects of LED lamps and luminaires used for general lighting were reviewed by an international team of researchers working under the 4E implementing agreement of the International Energy Agency (SSLC platform). Effects on the general population and subsets of sensitive groups were studied considering interactions with eye and skin, glare, circadian regulation, neuro-behavioral effects, effects of temporal light modulation, and long-term effects, such as age-related macular degeneration, myopia, and risks of cancer. This paper presents the conclusions and recommendations of the expert group. Knowledge gaps are detailed in each effect category.

**Keywords**—solid-state lighting, LED, health, sensitive population, photobiological safety, retinal damage, glare, discomfort, neuro-behavioral effects, temporal light modulation, flicker, circadian rhythm, biological clock, sleep, cancer, AMD, myopia

## I. INTRODUCTION

The relationships between light and health have been studied increasingly during the past decade following progress in physiology and medical science. Research results have important implications for lighting technology and practice. The report recently published by the IEA 4E Solid-State Lighting and Controls Platform [1] addresses the health effects of solid-state lighting (SSL) on people, with considerations of large fractions of the population as well as smaller sensitive groups of people. Different topics of light and health are addressed: photobiological safety, related to the effects of optical radiation on the skin and on the eye, glare, effects regulated by circadian rhythms, including sleep, acute neuro-behavioral effects, effects of temporal light modulation (TLM); and potential effects that may develop during periods of at least several years, such as age-related macular degeneration (AMD), myopia, and cancer.

## II. PHOTOBIOLOGICAL SAFETY

Several independent studies found that the retinal risk of acute exposure to light at the shortest wavelengths of the visible range (the blue-light hazard) is underestimated by current standards. Known sensitive populations are children,

persons without crystalline lens or wearing an intra-ocular lens (IOL) implant, elderly people, and subjects suffering from a preexisting eye disease. LED products used by sensitive people could be more reliably evaluated using lower exposure limits combined with a specific action spectrum. Because retinal sensitivity increases at night, people exposed to SSL at night can also be considered as a sensitive population.

### A. Recommendations

The photobiological safety standards addressing the blue light hazard should be revised to define more protective limits and more stringent emission requirements for products used by sensitive people, including children, people whose aversion response to bright light is not efficient, and night workers. Before these updates, it is not recommended to apply more permissive standards.

### B. Knowledge gaps

Beneficial effects of near-infrared (NIR) and red light were demonstrated on the retina, although it is not yet possible to apply these findings to improve lighting products. The effects of "spectrum enrichment" in preventing retinal damage are not known. The influence of the age factor, through the development of age-related retinal diseases, on the sensitivity of the retina to the shortest wavelengths of light should be further investigated.

## III. GLARE

Glare is the first cause of immediate dissatisfaction with lighting systems. It is experienced very quickly and is identified as a source of annoyance without ambiguity.

LED lamps and luminaire can have high luminance, or present high luminance contrasts with their background, inducing glare and subsequent discomfort in direct conditions of viewing. The luminance non-uniformity of many LED lamps and luminaires exacerbates discomfort from glare. Glare should be eliminated for persons suffering from migraines, as it can trigger or worsen headaches reinforcing their aversion to bright lights. Over several hours of exposure, glare contributes to eye strain. Discomfort experienced from
glare is likely to change with age and time of day, generally decreasing during the day, in the case of day-active people.

### A. Recommendations

Uniform luminaires with large area should be used in indoor lighting when the exposure time is long, as in schools and offices for instance. The non-uniformity correction of the unified glare rating (UGR) should be applied to assess glare from luminaires with non-uniform luminance used indoors.

The optical design of products should hide LEDs from direct view and should use diffusers. When these solutions are not applicable, guidance should be provided to users to promote the use of shading devices. Instructions should be given to avoid directing high intensity beams towards the viewer's eyes.

Migraineurs, people adverse to bright lights, people suffering from eye diseases, and children should avoid any direct viewing of high-luminance SSL sources. For these sensitive populations, both luminance and luminance contrasts should be reduced. Periodic patterns formed by dark and bright adjacent zones should also be avoided. Sensitive people should favor using warm-white lights, less likely to be glaring. Elderly people should not be exposed to glare for too long, in order to avoid potential delayed effects on visual performance.

People active during the night are intrinsically more sensitive to glare while being more exposed to it. The absence of daylight is responsible for higher luminance contrasts at night and higher discomfort experienced from glare.

### B. Knowledge gaps

The influence of the non-uniformity of lighting products based on LED arrays used outdoors should be investigated in conditions of close distance viewing by pedestrians. The effect of several simultaneous glare sources should also be studied in depth as this situation is very common in outdoor lighting.

There is currently no agreement on the spectral sensitivity to discomfort glare. The roles of the different photoreceptor types, including the photosensitive ganglion cells, are not known, although the influence of the circadian clock on glare has been demonstrated.

Knowledge about the brain mechanisms explaining visual light aversion and discomfort from glare have started to emerge but more studies are needed to fully understand them.

Glare is experienced more intensely by young adults, but the specific sensitivity of children is not known. Studies carried out with children would be useful to design better lighting systems for classrooms.

In people sensitive to glare, the dose-effect relations describing the probability and severity of eyestrain and headaches are not known.

## IV. TEMPORAL LIGHT MODULATION

Temporal light modulation (TLM) refers to rapid variations in the light emitted by lamps and luminaires, often caused by the power supply or dimmers.

Both human physiology and behavior are influenced by TLM, creating adverse effects on well-being and health. TLM is responsible for undesirable visual artefacts such as direct flicker, the stroboscopic effect, and the phantom array effect. Cognitive performance, brain activity and eye movements,

have been proven to be modified by TLM. Eyestrain, headache, and fatigue, are likely to occur particularly over long periods of exposure to TLM. Sensitive people, such as migraineurs, may develop such symptoms sooner and more severely. Some categories of people may experience debilitating symptoms such as photosensitive epileptic seizures. Currently, people cannot check if a lighting installation may create conditions that trigger these effects. Reducing TLM levels is a general precautionary principle to reduce the risks of unintentional exposure to TLM.

### A. Recommendations

Manufacturers should design lamps and luminaires to minimize the possibility of TLM at the product level (power supply, LED driver, dimmer). The use of pulse-width modulation (PWM) is common for dimming. Unfortunately, rectangular waveforms are responsible for the most problematic outcomes for observers. PWM should therefore be used with care, or replaced by other dimming techniques.

TLM should be systematically included in the list of specifications of LED lamps and luminaires. These specifications should be based on relevant standards and metrics. Mandatory limits at the product level should be set and be applicable to lamps and luminaires used at full power and at dimmed regime.

As a measure of public health, public spaces should not expose sensitive people to temporal light modulation.

### B. Knowledge gaps

The sensitivities to TLM should be studied with different populations, including migraineurs, and people in different age categories. The dose-effect relations between TLM and headaches, or TLM and eyestrain, are not known.

More data about brain activity are needed for modulation frequencies between 100 Hz and 1000 Hz and realistic temporal waveforms used by LED drivers and dimmers.

The severity of the visual effects of TLM should be based on validated metrics for all phenomena, including direct flicker, the stroboscopic effect and the phantom array effect. A standard metric for the phantom array effect is currently missing.

Task performance is affected by TLM. The assessment of visual comfort and acceptability of SSL products requires to measure longer term exposure data, typically over a duration of 8 hours.

## V. CIRCADIAN REGULATION

Circadian rhythms are exhibited by most physiological functions. They are regulated by the daily pattern of light and darkness. Short-wavelength light has a greater effect on the biological circadian clock, following the melanopic action spectrum.

The evaluation of the effects of light on circadian regulation relies on a proper assessment of individual exposure. When light exposure is not adequate, circadian perturbations disrupt sleep, nervous and endocrine systems, among other processes. In day active people, light exposure received in the morning advances the circadian clock. In the evening, light exposure has the reverse effect of delaying the clock. Light exposure history over the previous days moderates these effects, complicating the relations with sleep.
However, the concept of a healthy pattern of exposure to light and darkness is now well established.

### A. Recommendations

Public health authorities and occupational health and safety agencies should communicate more about the importance of light and dark exposure patterns.

Increasing daylight exposure and ensuring a high melanopic equivalent daylight illuminance (m-EDI) during the day should be recommended for all day-active people. SSL products used in the evening and at night should minimize m-EDI. This can be done by reducing the overall intensity of electric lighting and by using a higher level of long-wavelength light than short-wavelength light to provide enough light for vision during evening hours.

The consequence of promoting higher m-EDI values during the day is an increased energy use of electric lights indoors. Using better lighting controls and improving energy efficiency should help solving the apparent contradiction between energy savings and the need for a healthy dose of exposure to light in buildings.

### B. Knowledge gaps

The best light and dark exposure patterns should be defined for all people, including children and aging adults, night workers, shift workers, etc. Studies should investigate how sleep is affected by these patterns in these different populations. The impacts of light exposure patterns on other metabolic and neuroendocrine functions need to be better understood.

## VI. NEURO-BEHAVIORAL ASPECTS

Physiology and behavior are very quickly influenced by light exposure. Experimental studies have shown that a higher exposure increases self-assessed alertness. Stronger effects on alertness have been observed following evening exposures, as compared with exposures received in the morning or during daytime. However, the markers of alertness and cognitive performance provide inconsistent data. Better mood, vitality and social interactions have been generally reported by people exposed to higher levels of daily light. The available studies do not provide enough information to determine the optimal level of exposure associated with these positive effects.

### A. Recommendations

The healthy pattern of light exposure can be briefly summarized by “bright days, dark nights”. Recommended exposure levels during the night, the evening, and the day have been proposed following a scientific consensus. However, the question of reciprocity between amplitude and duration of the exposure has not been addressed.

### B. Knowledge gaps

More research is needed to examine the question of reciprocity. It would be very important to know if delivering a healthy light dose could be done during a shorter duration by using a higher light level. The reciprocity between light level and exposure time is of interest in all the areas involving the effects of light (cognition, sleep, circadian entrainment, well-being, etc.). More research would also be required to elucidate the relationships between the photosensitive retinal ganglion cells, the different types of photoreceptors, and the various neural pathways to the brain.

Although recent projects have found a link between exposure to long-wavelength light (red light and NIR optical radiation) and positive psychological and physiological outcomes, much remains to be learned about its potential use to improve lighting products. UV radiation might also present some positive aspects correlated with well-being, but photobiological safety requirements should not be ignored to protect the skin and the eye against potential adverse effects.

## VII. LONG-TERM EFFECTS

Several epidemiological studies and meta-analyses examined the occurrence of age-related macular degeneration (AMD) in several populations. They have reached conflicting conclusions, which make it impossible to conclude about the role of life-long light exposure.

The likelihood of myopia onset in children has been correlated with an insufficient time spent outdoors. Exposure to SSL have not been found to be responsible for myopia. An indirect link with LEDs may exist because the growing use of smartphones and tablets, equipped with LED displays, makes children more likely to spend too much time indoors.

There is a consensus among scientist about the link between the absence of adequate light-darkness exposure patterns over long periods of life and an increased risk of cancer. Several mechanisms are at play, involving circadian clock, melatonin secretion, inflammation, as well as epigenetic modifications of the action of genes involved in circadian regulation.

Several categories of people cannot receive a healthy dose of light exposure: people working in indoor environments deprived of daylight, people who have to sleep in lit environments, long-term night shifters, etc. These people are a special population who is more at risk because of the combination of an increased sensitivity to adverse effects and a higher exposure to these effects.

Nighttime work has been identified as a risk factor for cancer. However, no specific lighting technology can be associated with cancer.

### A. Recommendations

As a measure of precaution against a possible early onset of age-related retinal diseases, people working under strong electric lights should avoid looking repeatedly at high power SSL luminaires. Stage artists and lighting professionals are concerned, among other categories of workers.

For the population who cannot access daylight, initiatives should be taken to increase daily light exposure and promote darker nighttime environments. Nursing homes, long-term care facilities, and prisons should implement such measures to help maintain the individual and collective quality of life in their premises.

The prevention of myopia requires to regularly expose children to daylight during the school day, especially in elementary schools. People living or working in prisons, hospitals, long-term care facilities, nursing homes, are often deprived from daylight. Adaptations of work schedules, working and living areas would be needed to promote a better quality of life thanks to an increased exposure to light at the proper time and level.
## B. Knowledge gaps

The role of the shortest wavelengths of light (violet, blue) in the growth of the eyeball during childhood would have to be studied in details to better understand the mechanisms behind the onset of myopia in children.

The effect of the life-time environmental exposure to electric light should be studied to better understand the link with the aging of the retina and with the development of AMD. Epidemiological studies relying on the assessment of individual light exposure at the eye and the separation of daylight, electric lights and light from displays would be needed.

## VIII. CONCLUSIONS

A large variety of psychological and physiological processes are dependent on light. The pattern of individual exposure to light and darkness plays the most important role in the potential risks and benefits associated with these effects. Electric lighting is responsible for a significant and growing fraction of the overall light exposure, motivating the assessment of health effects of new technologies. Solid-state lighting technologies have replaced legacy light sources because of energy and environmental considerations, but they also contributed to increase the demand for light, and therefore the exposure levels.

Overall, solid-state lighting has not been found to present new health hazards. However, LED lamps and luminaires can have a very wide range of characteristics, increasing the probability of being adversely exposed to inadequate light levels, unbalanced spectral distributions and wrong timing that are not part of a healthy pattern of exposure. Considering solid-state lighting as a highly diversified product category, there are better and worse individual products. Nevertheless, even the best product can be badly used, depending on the awareness of potential health issues it may pose and the consideration of these issues in standards, regulations and everyday lighting practices.

Given the diversity of solid-state lighting products, sensitive people have more chances to be exposed to adverse effects, whether they are aware of it or not. For this reason, these individuals should be better protected by defining and enforcing more protective limit values. These limits should be applicable at the product level, through mandatory reporting and labelling, or used to check lighting systems whenever they are installed in buildings or cities.

In most countries, national energy regulations cover electric lighting with the objective of limiting its energy consumption and prescribing light levels needed to ensure acceptable visual performance. This approach does not consider the current knowledge about the healthy dose of light exposure that people should receive during the day. This dilemma should be addressed by revising standards and regulations to make sure that everyone has access to the best quality of lighting and can receive a healthy dose of light during the day. A closer collaboration of energy regulators with public health agencies is required to reach this goal.

## ACKNOWLEDGMENT

The authors wish to express their gratitude to the management committee and experts of the IEA 4E SSLC Platform. The authors are grateful to the member governments for their support of this work, as well as the Australian

Radiation Protection and Nuclear Safety Agency, Natural Resources Canada, the National Research Council of Canada, and the Agency for Ecological Transition (ADEME).

## REFERENCES

[1] C. Martinsons, J. A. Veitch, S. Loughran, A. Nixon, R. Mate, R. Harris, L. Shen, "Solid-state Lighting: Review of Health Effects", ISBN: 978-1-83654-223-0, Eds. International Energy Agency 4E SSLC Platform, Stockholm, Sweden, 2024