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Are LEDs really harmful to health?

March 2018, by Alan Grant, Design and Development Director

Where do the ‘danger edges’ lie for blue light, and blue light hazard?

LEDs have come a long way in recent years. The multitude of types, efficacies, colour temperatures and colour quantity have increased dramatically, and improvements continue to be made. The benefits of LED are vast and well documented. But how much do we really know about this evolving technology, a technology that is moving so fast that neuroscience, photobiology and lighting standards are struggling to keep up?


For manufacturers, the LED revolution has proved a radical departure from lamp technology and a steep learning curve, but many innovative products would not exist today without it. In some respects, we (the lighting industry) started from the wrong place with early LED technology, particularly in street lighting, where there was an emphasis on trying to match the performance of established lamp technology.

Now, as the market is beginning to mature, it’s easy to look back and criticise early LED products, with their poor optical control and very high CCT (by today’s standards). Yet this was the only way to achieve the required lumen output and meet the lighting design requirements.

Add to this some poor installations – too close to properties, with significant light trespass and no shielding. The result? Unhappy residents and some pretty bad press, particularly in the UK and US, with regards to glare and brightness of LED lighting, potential health concerns and sleep deprivation.

Addressing the evidence

In 2016, in the US, a report from the American Medical Association (AMA) entitled Human & Environmental Effects of Light Emitting Diode Community Lighting caused a stir and some backlash amongst lighting professionals[1]. One of its notable conclusions was that the use of colour temperature lower than 4000K 'will minimise potential health and environmental effects' (of LED lighting), which fuelled the adverse-press-reports fire.

Also in 2016, in the UK, Public Health England (PHE) published a report commissioned by CIBSE & the SLL entitled Human Responses to Lighting Based on LED Lighting Solutions which covered both interior and exterior lighting[2]. One of its conclusions was: 'Consideration should be given to reducing the CCT (below 4000K); avoiding potential adverse effects on melatonin production in the evening '. Both reports made recommendations related to colour temperature, but only PHE explained why.

In July 2017, one of the two independent scientific committees within the European Commission, The Scientific Committee on Health, Environment and Emerging Risks (SCHEER), which represents the opinion of the independent scientists committee members and several external experts including a leading PHE scientist, published its Preliminary Opinion on Potential Risks to Human Health of Light Emitting Diodes[3].

For lighting professionals, this is perhaps the most relevant report. It is the most recent and it used papers and reports published in international scientific journals, including up-to-date research, in this fast-moving area of science. The committee’s report concluded that: 'There is no evidence of direct adverse health effects from LEDs emission in normal use (lamps and displays) by the general healthy population. There is a low level of evidence that exposure to light in the late evening, including that from LED lighting and/or screen, may have an impact on the circadian rhythm. At the moment, it is not yet clear if this disturbance of the circadian rhythm leads to adverse health effects'.

The conclusion continued that, 'there are studies conducted on animals showing adverse effects (of exposure to white LED lighting) raising concerns particularly in the susceptible population (young children, adolescent and elderly people), but that the results obtained in these studies were using exposure conditions that are difficult to relate to human exposure'.

Furthermore, 'reliable information on the dose-response relationship for adverse health effects for the case of the healthy general public is not available in the scientific literature for all wavelengths emitted by LED devices'.

So, are the LEDs harmful to health?

To pick the bones out of this, the headline here is that there is currently no evidence of direct health effects from LED emission in normal use by the general healthy population.

The committee qualifies this statement by identifying those who are not within the ‘general healthy population’ as follows: 'Vulnerable and susceptible population (young children, adolescent and elderly people) have been considered separately. Children have a higher sensitivity to blue light and although emissions may not be harmful, blue light (between 400nm and 500nm) may be very dazzling and may induce photochemical retinopathy, which is a concern, especially for children below three years of age. The elderly population may experience discomfort with exposure to LED systems, including blue LED display (for example destination displays on the front of buses will be blurred)'.

The effects on children

From this, we can surmise that children, and particularly those under three years of age, are particularly susceptible to blue light. A quote from the SCENIC[DB1] R (European Commission Scientific Committee on Emerging and Newly Identified Health Risks) explains this as follows. 'A child’s crystalline lens is more transparent to short wavelengths than that of an adult, making children more sensitive to blue light effects on the retina' [4].

A quick look at Wikipedia defines photochemical retinopathy as: 'damage to the eye’s retina, particularly the macula, from prolonged exposure to solar radiation or other bright light, eg lasers or arc welders. The term includes solar, laser, and welder’s retinopathy and is synonymous with retinal phototoxicity. It usually occurs due to staring at the sun, watching a solar eclipse, or viewing an ultraviolet, Illuminant D65, or other bright light' [5]. Anyone who has welded or studied welding will be aware of the term ‘arc eye’, which is photo-retinopathy.

The ageing population

It is well-known and well-understood that the human eye degrades over time. This is evident in the large proportion of those aged over 40 who require glasses for reading, distance vision or both. The bad news therefore contained in the report is that elderly people may experience discomfort with exposure to LED systems, including blue LED displays (which may include white LEDs with a high colour temperature and therefore typically a blue light content) making it difficult to read.

With the passage of time, the proliferation of LED-illuminated displays or signs will only increase. We know that the proportion of over-60s in the UK population is also increasing. At present about 25% of the population is aged over 60, or the equivalent of 15.3 million people. By 2035, this is predicted to be 29%, or around 21 million people. The statement from SCHEER is therefore not great news for this ‘vulnerable and susceptible’ population.

Key takeaways

There are a few other statements from the body of the SCHEER opinion that are worthy of note for lighting professionals. 'Many people perceive white 4,000K LED lighting as harsh because almost 30% of the spectrum is emitted as blue light'. We can dissect this statement word by word, and I’m sure many readers will do just that.

For me, the colour of white light is subjective, and application should play a part in the user’s choice of colour temperature. One person’s ‘harsh’ is another person’s ‘clean’ or ‘bright’. Many people prefer a ‘whiter’ light (say 4000K) in a kitchen or workshop and a warmer colour (say 3000K) in a living room. The percentage stated (30%) is not common between different LED sources, and so is highly questionable.

There are several variables to be taken into account when referring to the effects of optical radiation from LEDs on human health:

  1. Spectrum of a LED light source
  2. Intensity of the lighting, especially in the blue band
  3. Duration of exposure
  4. Health of the eye
  5. Direct staring without deviation versus active eye movement

Taking these points one at a time, the spectrum of an LED light source (1) in full is the spectral power distribution of the light source (SPD). This is illustrated as the combination of the range of wavelengths within the visible spectrum that produce the colour of light perceived by the human eye. Note that the CCT of a light source is not mentioned in this list, although it was mentioned in both the AMA and PHE’s recommendations and in the SCHEER statement above, with regards to perception of harsh lighting. The reason for this is simple. With very few exceptions, those in the lighting industry refer to the colour of the white light emitted from an LED (or other) light source in terms of CCT: 4000K, 3000K, 2700K for example.

It’s a simple and well-understood means of communicating the appearance of the colour of the light but, there is no correlation between CCT and SPD. Light sources of the same CCT can have different SPDs and those with the same CCT can look different, so CCT is only a rough guide of the actual spectral content of a light source.

Let’s address this statement starting with point 1. Clearly, the SPD of a light source will be important to the effect of optical radiation, as it is well understood that emissions of part of the visible spectrum influence brain stimulus.

The intensity of light (2) is again self-explanatory. A bright light source will have a different, potentially stimulating effect on human physiology than a very dim light. Relatively low-intensity levels (<100lux) have been reported to affect the circadian system (Glickman, Levin et al. 2002)[6].

The duration of the exposure (3) is again something we can all probably relate to and even short durations (seconds to minutes) can have an effect on circadian system (Glickman, Levin et al. 2002). The health of the eye (4) covered earlier in this article (children’s lenses not being fully developed and the lenses in the eyes of elderly people hardening (from middle age onwards) resulting in difficulty to focus). Direct staring without deviation versus active eye movement (5) can lead to photo retinopathy, described earlier and affect the circadian system.

Influencing the circadian rhythm

I’ve mentioned circadian rhythm and circadian system above and the statement within the SCHEER opinion: 'Short-wavelength light (peak around 480nm) influences the circadian system'  also raises the issue of it being affected by light within the blue part of the spectrum.

The presence of a light (day) and dark (night) phase due to the earth’s rotation has resulted in the evolution of an internal clock in almost all organisms, including humans, as SCHEER makes clear. This biological timekeeping system influences the timing of our sleepiness, hunger and willingness to be active through to unconscious physiological patterns, such as the preparation of internal organs for daily activities and the ‘decision’ to wake from sleep, immune response and energy metabolism.

Ambient light levels are the main information our bodies use to synchronise themselves (Andersen 2012)[7].

There is a body of evidence to support that chronic impairment of the circadian system has been shown to compromise health in many ways: sleep and cognitive impairment, psychiatric disorders, gastrointestinal disorders and breast cancer (Knutsson 2003, Kecklund & Alexsson 2016)[8].

Therefore, the statement from SCHEER that 'Short-wavelength light (peak around 480nm) influences the circadian system'  should be taken seriously. As well as the image-forming function of our eyes, there are cells within human and other mammalian eyes that perform non-image forming functions including pupillary light reflex. Called intrinsically photosensitive retinal ganglion cells (ipRGC), these also relay light information to the part of the brain (the suprachiasmatic nucleus of the hypothalamus) that controls the biological clock.

This, in turn, initiates signals to other parts of the brain to release hormones (for example melatonin and cortisol) related to daily activities as outlined above. The ipRGCs contain a photopigment called melanopsin with a peak sensitivity of 480- 490nm (Lucas 2014) [9] which is why the SCHEER made the statement: 'Short-wavelength light (peak around 480nm) influences the circadian system'.

Referring back to the 2016 PHE report mentioned earlier in this article, this states that: 'Consideration should be given to reducing the CCT (below 4000K); avoiding potential adverse effects on melatonin production in the evening'. The two reports – PHE and SCHEER – therefore appear to be aligned in their research, but not in their conclusions.

The conclusion

In summary, the latest research from an independent scientific body (SCHEER) states: 'There is no evidence of direct adverse health effects from LEDs emission in normal use (lamps and displays) by the general healthy population. There is a low level of evidence that exposure to light in the late evening, including that from LED lighting and/or screens, may have an impact on the circadian rhythm. At the moment, it is not yet clear if this disturbance of the circadian rhythm leads to adverse health effects'.

It goes on to say: 'Since the use of LED technology is still evolving, the Committee considers that it is important to closely monitor the risk of adverse health effects from long-term LED usage by the general population'. There are hundreds, possibly thousands, of research papers and articles on this subject and the number is steadily growing. There is, however, insufficient research and evidence for experts to draw clear and concise conclusions on this complex and relatively new subject. Its importance cannot be underestimated though. LED lighting is a recent revolution which is sweeping the globe for many good reasons, but it is in its infancy.

SCHEER has identified the 'vulnerable and susceptible population'  to be outside the core statement, 'no evidence of direct adverse health effects from LEDs emission in normal use'.

We’ve only been exposed to LED emissions for a small number of years, after previous exposure to other types of light sources. As the years pass, today’s toddlers will become adults who will have only been exposed to LED lighting. The ever-increasing ageing population will have had exposure from a far younger age.

Manufacturers, designers, specifiers and installers – we all have our part to play as lighting professionals. We should all take care with the application of this technology, ensuring that good lighting control, appropriate distributions, shielding, dimming, colour temperature and other facets of LED lighting are used responsibly and proactively. It is too simplistic simply to choose a 3000K (or lower) colour temperature without consideration to the SPD of the light source.

This has always been the case with lighting, before the LED revolution as well as today. 

But it has never been more important for our industry and the general population, both healthy and susceptible.


[1] Human & Environmental Effects of Light Emitting Diode Community Lighting, American Medical Association, 2016, https://www.ama-assn. org/sites/default/files/ media-browser/public/about-ama/councils/Council%20Reports/council-on-science-publichealth/a16-csaph2.pdf

[2] Human Responses to Lighting Based on LED Lighting Solutions, Public Health England, SLL, CIBSE, April 2016, http://www.lightmare.org/docs/PHE-CIBSE-SLL_LED_report_May2016HRLBL-b.pdf

[3] Preliminary Opinion on Potential Risks to Human Health of Light Emitting Diodes, European Commission, The Scientific Committee on Health, Environment and Emerging Risks, 06 July, 2017, https://ec.europa.eu/health/sites/health/files/scientific_committees/scheer/docs/scheer_o_011.pdf

[4] Health Effects of Artificial Light, European Commission, Scientific Committee on Emerging and Newly Identified Health Risks, 19 March, 2012, http://ec.europa.eu/health/scientific_committees/emerging/docs/scenihr_o_035.pdf

[5] Photic retinopathy, Wikipedia, 2017, https://en.wikipedia.org/wiki/Photic_retinopathy

[6] Ocular Input for Human Melatonin Regulation: Relevance to Breast Cancer, G Glickman, R Levin and G C Brainard. Neuroendocrinology Letters, 2002, 23 Suppl 2: 17-22.

[7] A Framework for Predicting the Non-visual Effects of Daylight – Part I: photobiology-based model, Andersen M, Mardaljevic J and Lockley SW (2012). Lighting Research and Technology, 44(1), 37-53.

[8] Health disorders of shift worker, Knutsson, A. Occup. Med. 53, 103-108 (2003). https://doi.org/10.1093/occmed/kqg048

[9] Measuring and Using Light in the Melanopsin Age, Lucas RJ, Peirson SN, Berson DM, Brown TM, Cooper, HM, Czeisler CA, Figueiro MG, Gamlin PD, Lockley SW, O’Hagan JB, Price LLA, Provencio I, Skene DJ and Brainard GC (2014). Trends in Neurosciences, 37(1), 1-9.