The blue light issue has several aspects. First one needs to separate between the tiny bright blue diods used on some electronic devices, the blue-white light from white LEDs, CFLs and xenon arc car headlight lamps, and the (more or less) warm-white light from incandescent-mimicking CFL and LED.
This blog is primarily about replacement lamps for general illumination, not signal lights, monitor backlighting and the like, but the information on bright blue light may still be relevant for the cool-white light as well.
Let’s start with the bright blue lamps. From the Wikipedia LED page:
Blue hazard: There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1–05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.
This web article Blue LEDs: A health hazard? explains the problems with bright blue light in detail:
Blue appears brighter at night
Firstly, blue light appears much brighter to us at night, or indoors where ambient light is low – an effect known as the Purkinje shift. This is because the rods – the sensitive monochromatic rod light detectors which our retinas rely on more at night – are most sensitive to greenish-blue light. (Some hypothesize that animals evolved the rods in underwater and jungle environments, hence the bias to blue or green – later we developed separate full color vision on top of that system, but the sensitive rods remained).
A practical example of the Purkinje Shift: a cool blue power LED on a TV might catch your eye and even attract you to buy it in a well-lit store. But after you take it home, the same LED appears distractingly bright when you watch the TV in a darkened room.
And blue is brighter in peripheral vision
The Purkinje shift also noticeably brightens blue or green lights in our peripheral vision under medium to low light conditions, because there are comparatively more rods towards the edge of the retina – hence complaints that blue LEDs are distracting even when they’re not the focus of attention.
“Glaring LEDs on displays that you need to see at night… that’s poor design,” says Brandon Eash. Remarkably though, it is a mistake that manufacturers continue to make.
Blue does not help you see clearly
We tend to associate blue with coolness, accuracy and clarity. But paradoxically, our eyes cannot focus blue sharply. We actually see a distracting halo around bright blue lights.
“It’s well recognized that blue light is not as sharply focused on the retina as the longer wavelengths. It tends to be focused in front of the retina, so it’s a little out of focus,” explains Dr. David Sliney, a US Army expert on the physiological effects of LEDs, lasers, and other bright light sources.
The various wavelengths of light focus differently because they refract at slightly different angles as they pass through the lens of the eye – an effect known as chromatic aberration.
For similar reasons, blue scatters more widely inside the eyeball, says Dr. Sliney, who answered questions by phone last year from his office at the US Army Center for Health Promotion and Preventive Medicine in Maryland.
We’re half blind in blue
The modern human eye evolved to see fine detail primarily with green or red light. In fact, because we are poor at distinguishing sharp detail in blue, our eyes don’t really try. The most sensitive spot on the retina, the fovea centralis, has no blue light-detecting cones. That’s right: we’re all color blind in the most sensitive part of our eyes.
In addition, the central area of the retina, the macula, actually filters out some blue light in an effort to sharpen our vision. Snipers and marksmen sometimes improve on nature by wearing yellow-tinted ‘shooters glasses’, which block the distracting blue light.
“You throw away a little bit of color information in order to have a sharper view of things,” explains Dr. Sliney.
Blue glare interferes with vision
The twin effects of fuzzy focus and blue scatter both make intense blue light from a point source, like an LED, spread out across the retina, obscuring a much wider part of our visual field.
Although our retinas simply don’t handle blue very well, nobody told the rest of the eye that. If blue is the strongest color available and we want to see fine detail, then we strain our eye muscles and squint trying to pull the blue into shaper focus. Try to do this for too long and you’ll probably develop a nauseating headache. This won’t happen in a normally lit scene, because the other colors provide the sharp detail we naturally desire.
A dazzling pain in the eye
By the way, the physical pain some people feel from high intensity discharge (HID) car headlights and particularly intense blue LEDs seems to be a combination of these focus and scatter effects, together with a third. We have a particularly strong aversion reaction to bright blue light sources, including bluish-white light. “Pupilary reflex is down in the blue [part of the spectrum]. The strongest signal to the muscles in the iris to close down comes from the blue,” says Dr. Sliney.
Intense blue light can cause long-term photochemical damage to the retina. Now, nobody is claiming that you’re likely to suffer this kind of injury from a normal blue LED (unless you stare fixedly at it from a few millimetres for an hour). However, it is theorized that this may be the evolutionary driving force behind the immediate feeling of pain we get from bright light with a very strong blue component.
Our body’s instinctive reaction is to reduce blue light entering the eye by closing down the pupil. This means that blue light spoils night vision. After a brief flash of blue, you can’t see other colors so well for a while.
When it comes to lamps for general illumination, the issue gets more complex. Cool-white or daylight-mimicking indoor illumination may not be as good for vision as previously assumed. But can it be harmful?
CELMA-ELC-GLA (lighting industry):
In June, PLDA Greenpages blog reported on new studies that “have concluded that LEDs present no greater optical hazard than other common artificial lighting sources”. The link required business and registration to be accessed, but the abstract appears to be the same as in this March 2012 white paper of the Global Lighting Association on The Optical & Photobiological Effects of LED, CFLs and Other High Efficiency General Lighting Sources, which in turn appears to be fairly identical to the July 2011 position statement from CELMA and ELC (European luminare and lamp manufacturers, respectively): Optical safety of LED lighting.
If it is the same document, I wouldn’t exactly call it a study as it only gives technical explanations of why LEDs and CFLs belong to risk groups 0 or 1, which may be correct, but cites no studies on actual health effects; it’s all just extrapolation of their own data. Quoting some relevant parts of the document (not all in original order):
Potential effects on the eye
Commonly discussed hazards affecting the eye are blue light hazard (BLH) and age‐related macular degeneration (AMD) which can be induced or aggravated by high intensity blue light. Furthermore, UV (ultraviolet) may affect the eye, causing cataract or photokeratitis (sunburn of the cornea); IR (infrared) radiation can induce IR cataract (also known as glassblower’s cataract); and, radiation of all wavelengths can lead to retinal thermal injuries at extreme intensities.
Potential effects on the skin
Optical radiation, particularly UV can be harmful to the skin. By far the most hazardous source to consider is the sun. Sunburns (UV erythema) and skin cancers due to long‐term exposure to the sun are well‐known problems caused by radiation. Moreover, patients with autoimmune diseases such as lupus or photodermatoses can be highly sensitive to UV radiation, and sometimes also blue light. There is concern among some patients who suffer from such sensitivities that phasing out of the known incandescent lamps will leave them without lamps for indoor use that are low in radiation of UV and blue light.
4.1 Conclusions on blue light emission
Evaluation at a distance producing 500 Lux: Taking the 500 Lux criterion as the measurement basis, none of the LED products belongs to risk group 2. This was also confirmed by a study of the French agency for food, environmental and occupational health & safety (ANSES) in 2010 which found that even high‐output discrete LEDs are classified into risk groups 0 or 1 if the 500 Lux criterion is applied.
Precautionary measures with regard to children
The lens of a child’s eye filters blue light less efficiently than an adult’s lens. Children are thus more sensitive to blue light hazard. Therefore, at places frequented by children particular care must be taken to ensure that lamps and luminaires are chosen and installed in such a way as to avoid people looking directly into the light source. It is not necessary that LEDs (or blue light in general) are avoided in an environment with children present, for the reasons stated above. If used across a broad surface or area, in a way which does not produce glare, even “pure” blue light is completely harmless; regardless of whether it is the blue in daylight or produced by LEDs or other light sources.
Guidance for people with high sensitivity for blue light
The above statements are valid for healthy people in the general public. People with highly sensitive skin or eyes for blue light may be wise to investigate alternative light sources that operate on a more specific radiation band not covered by the applied action curves that cover a broad range of radiations. The comparative data given in the annexes of this paper serve to give guidance in selecting the best available type of light source for a given sensitivity.
The biological importance of blue light
It needs to be mentioned that blue light exposure is important to human beings. Blue light with a peak around 460‐480nm regulates the biological clock, alertness and metabolic processes. CELMA‐ELC has installed a special working group to translate these findings into practical application norms and standards. In natural conditions, outdoor daylight fulfils this function. Yet, people spend most of the day indoors (offices etc.) and are often lacking the necessary blue light exposure. Blue and cool white light sources can be used to create lighting conditions such that people will receive their daily portion of blue light to keep their physiology in tune with the natural day‐night rhythm. Due to the highly flexible application possibilities, LED based light sources are particularly well suited for that purpose.
Annex 3: Blue light radiation data of light sources
When evaluating the risk of blue light hazard posed by LED (and other) light sources, two fundamentally different cases need to be considered:
Case A: Looking at an illuminated scene
[...] Case A can generally be considered safe. To give an example, looking at the scattered blue sky (high blue irradiance but low radiance) is completely safe, and so are artificial light sources, containing way less blue irradiance than daylight.
Case B: Looking at a light source
[...] Looking straight at a light source (case B) is also in general safe for diffuse and warm white light sources, like frosted or white diffusing lamps. Yet, caution is advisable for cool white or blue, bright (high intensity), point‐like light source, for instance an incandescent filament, electric arc or an LED die, even an LED die behind the lens of a directional lamp. Such point‐like sources are projected on the retina as a concentrated light spot and can damage that spot on the retina when the intensity is high enough and the spectrum contains blue light in congruence with the blue light hazard action spectrum curve.
4.2 Conclusions on ultraviolet radiation (UV)
LED based light sources do not emit any UV radiation (unless specifically designed for that particular purpose). Therefore, they are not harmful to people with a specific sensitivity for certain UV radiation and can bring relief to certain groups of patients. In this respect, LED based light sources provide advantages over traditional incandescent, halogen and Compact Fluorescent lamps. For more details see Annex 2.
4.3 Conclusions on infrared radiation (IR)
In contrast to most other light sources, e.g. halogen and incandescent lamps, LEDs hardly emit IR light (unless specifically designed to emit a certain type of IR). For available types of indoor light sources the IR radiation is not powerful enough to pose any risks to human.
To summarize the key findings, LED sources (lamps or systems) and luminaires are safe to the consumer when used as intended.
Which is: Don’t sit too close to a UV-emitting light source. Don’t look straight into cool-white or bright light sources (risk increases with proximity, brightness and time). Always use low-voltage halogen mini bulbs and halogen mini tubes on luminaires with glass cover (regular glass filters out the UVC which the quartz glass lets through). Use warm-white LED, CFL or halogen in frosted outer bulb if UV-sensitive.
In terms of their level of photo biological safety, LED lamps are no different from traditional technologies such as incandescent lamps and fluorescent tubes. The portion of blue in LED is not different from the portion of blue in lamps using other technologies at the same colour temperature.
The last sentence seems a bit tautologous as otherwise it would not have the same colour temperature. How the blue portion can be “the same” for same colour temperature LED and incandescent despite their different spectral power distribution is given an explanation:
White LEDs typically show a peak in the blue (at around 450 nm when a royal blue LED is used) and more broadband emission in the green/yellow part of the spectrum. Next to the blue peak, a dip is visible at around 490nm that also falls under the BLH action curve (…). The blue peak of the LED lamps is “compensated” by the dip, therefore the total blue output (…) of LED of 2700K is comparable to an incandescent lamp of 2700K.
This still does not make the spectrum exactly the same, even if the net result is a similar blueness. And most LEDs available on the home market is very much bluer than the 2700 K of the very best (and most unaffordable) warm-white LEDs.
Nevertheless, looking straight into bright, point‐like sources (LEDs, but also other strong point‐like light sources, like clear filament or discharge lamps and including the sun) should be prevented. However, when people happen to look into a bright light source accidentally, a natural protective reflex occurs (people instinctively close their eyes or look away from the source).
A comparison of LED retrofit products to the traditional products they are intended to replace reveals that the risk levels are very similar and well within the uncritical range.
But that was for the 6 watt warm-white LED in a frosted outer bulb included in the comparison. White 4000 K LEDs and directional high power LEDs, as well as other bright point light sources, including clear tungsten filament lamps, fall into risk group 1.
The bar chart included in the document shows that the higher the CCT, the higher the blue light hazard, regardless of light source (as would be expected);
(Two other bar charts (fig. 5 & 6) quite strangely compared frosted warm-white LED lamps with clear incandescent lamps, in order to make incandescent light appear to to have more blue light, rather than to compare it with the other point-like sources. In those charts, the frosted incandescent lamp seemed to be the safest.)
In 2011, SCENIHR, the European Commissions Scientific Committee on Emerging and Newly Identified Health Risks (one of the independent scientific committees of the European Commission, which provide scientific advice to the Commission on consumer products) issued an updated report on Health Effects of Artificial Light which seems partly based on the information given by European Lamp Companies Federation, ELC (extracts, emphases added):
A: Potential health impacts on the general public caused by artificial light
In general, the probability is low that artificial lighting for visibility purposes induces acute pathologic conditions, since expected exposure levels are much lower than those at which effects normally occur, and are also much lower than typical daylight exposures. Certain lamp types (quartz halogen lamps, single- and double-capped fluorescent lamps as well as incandescent light bulbs) may emit UV radiation, although at low levels. However, according to a worst case scenario the highest measured UV emissions from lamps used typically in offices and schools [usually fluorescent tubes] could add to the number of squamous cell carcinomas in the EU population.
Household lighting involves an illumination level which is so low that exposure to potentially problematic radiation is considered negligible. There is no consistent evidence that long-term exposure to sunlight (specifically the blue component) may contribute to age-related macular degeneration (AMD). Whether exposure from artificial light could have effects related to AMD is uncertain.
No evidence was found indicating that blue light from artificial lighting belonging to Risk Group 0 (“exempt from risk”) would have any impact on the retina graver than that of sunlight. Blue light from improperly used lamps belonging to Risk Groups 1, 2, or 3 could, in principle, induce photochemical retinal damage in certain circumstances. There is however no evidence about the extent to which this is actually occurring in practical situations.
There is mounting evidence suggesting that ill-timed exposure to light (light-at-night) may be associated with an increased risk of breast cancer, and can also cause sleep disorders, gastrointestinal, and cardiovascular disorders, and possibly affective states. Importantly, these effects are directly or indirectly due to light itself, without any specific correlation to a given lighting technology.
But bluer light (such as from cool-white or daylight LEDs and CFLs) has a greater effect on melatonin, even at very low intensities if used at night (see Circadian Rhythms below).
B: Aggravation of the symptoms of pathological condition
The SCENIHR opinion on Light Sensitivity identified that some pre-existing conditions (epilepsy, migraine, retinal diseases, chronic actinic dermatitis, and solar urticaria) could be exacerbated by flicker and/or UV/blue light. At that time there was no reliable evidence to suggest that compact fluorescent lamps (CFLs) could be a significant contributor. More recent studies indicate a negative role for certain CFLs and other artificial light sources (sometimes including incandescent bulbs) in photosensitive disease activity.
UV, and in some patients, visible light can induce skin lesions of true photodermatoses. Although sunlight is reported by most patients as the main source of disease activity, artificial lighting is reported to play a role in some cases. The blue or UV components of light tend to be more effective than red components in aggravating skin disease symptoms related to pre-existing conditions such as lupus erythematosus, chronic actinic dermatitis and solar urticaria. UV and/or blue light could also possibly aggravate the systemic form of lupus erythematosus. It is recommended that all patients with retinal dystrophy should be protected from light by wearing special protective eyeware that filters the shorter and intermediate wavelengths.
3.3.3. Lamp emissions
Based on emissions from the lamp, the Standard EN 62471 (and also IEC 62471 and CIE S009, since they are all identical in this sense) categorizes the lamps according to the photo-biological hazard that they might pose. The different hazards are:
1. Actinic UV-hazard for eye and skin (see section 188.8.131.52);
2. UVA-hazard for the eye (section 184.108.40.206);
3. Blue-light hazard for the retina (section 220.127.116.11);
4. Thermal retina hazard (section 18.104.22.168) and
5. IR-hazard for the eye (sections 22.214.171.124 and 126.96.36.199).
According to the standards, measurements should be performed according to two approaches; viz. at a distance where a light intensity of 500 lx is obtained and also at a distance of 20 cm (…). Based on these measurements, lamps are then classified according to the “Risk Group” (RG) to which they belong. RG0 (exempt from risk) and RG1 (minor risk) lamps do not pose any hazards during normal circumstances. RG2 (medium risk) lamps also do not pose hazards because of our aversion responses to very bright light sources, or due to the fact that we would experience thermal discomfort. RG3 (high risk) include only lamps where a short-term exposure poses a hazard. This classification is based on acute exposure responses (a single day, up to 8 hours) and applies only to individuals of normal sensitivity.
The contribution from the European Lamp Companies Federation (ELC) included six lamp types from eight manufacturers, considered by ELC to be “representative lamp types”.
188.8.131.52. Assessment of effects on the healthy eye
Discomfort glare does not impair visibility but causes an uncomfortable sensation that causes the observer to look away from the glaring source. It increases when the light source is facing the observer.
Disability glare is due to the light scattering within the ocular media which creates a veil that lowers any contrast and renders viewing impossible.
The luminance of the sky is rather stable at about 5,000 cd/m2. This value can be exceeded on bright surfaces on clear days when luminance can reach several tens of thousands cd/m2. The sun is never viewed directly except when it is at sunrise or at sunset when its luminance is about the same as the sky and its colour temperature low or moderate.
It is when both the luminance and the colour temperature of the light are high that the blue light hazard increases.
The UV/blue light risk on the healthy majority is considered by ELC to be very low and SCENIHR accepts this, but with some questions regarding high power LEDs, wrong use and “non-representative lamps” (= lamps other than the “representative lamps” submitted to SCENIHR by the ELC):
The results presented in the ELC report suggest to SCENIHR that there is little or no risk to individuals of normal sensitivity from the UV, IR or blue light optical radiation emission from lamps which are considered to be “representative” of the type of lamps selected to replace incandescent lamps. SCENIHR however considers that “non-representative” lamps may emit levels that are much higher than those included in the report; however quality control limits applied by lamp manufacturers were not reported. Further consideration should also be given to the “intended” vs. “reasonable foreseeable” use of lamps. Further consideration also needs to be given to the risk classification of high power LEDs. Also, halogen lamps that are intended to be used with an external glass filter must not be used without the filter because of the risk of exposure to UV radiation.
184.108.40.206. Circadian rhythms
Recent studies indicate that ill-timed exposures to even low levels of light in house-hold settings may be sufficient for circadian disruptions in humans.
A comparison between the effects of living room light (less than 200 lx) and dim light (<3 lx) before bedtime showed that exposure to room light suppressed melatonin levels and shortened the duration of melatonin production in healthy volunteers (18-30 years) (Gooley et al. 2011).
Cajochen et al. (2011) compared the effects of a white LED-backlit screen with more than twice the level of blue light (462 nm) emission to a non-LED screen on male volunteers. Exposure to the LED-screen significantly lowered evening melatonin levels and suppressed sleepiness.
In another study from the same group (Chellappa et al. 2011) 16 healthy male volunteers were exposed to cold white CFLs (40 lx at 6,500 K) and incandescent lamps (40 lx at 3,000 K) for two hours in the evening. The melatonin suppression was significantly greater after exposure to the 6,500 K light, suggesting that our circadian system is especially sensitive to blue light even at low light levels (40 lx).
However, no study has investigated whether the impact of warm white CFLs and LEDs (2,700-3,000 K) on melatonin suppression is in any way different from that of incandescent lamps.
There is a moderate overall weight of evidence that ill-timed exposure to light (light-at-night), possibly through circadian disruption, may increase the risk of breast cancer.
There is furthermore moderate overall weight of evidence that exposure to light-at-night, possibly through circadian disruption, is associated with sleep disorders, gastrointestinal and cardiovascular disorders, and with affective disorders.
The overall evidence for other diseases is weak due to the lack of epidemiological studies.
It seems that bright white light in the daytime can be helpful in keeping one alert for work (though preferably the real thing rather than a daylight-mimicking copy). But at night – very bad idea! Unless you’re doing shift work and really need to stay awake.
I have started noticing the effect of bright white light at night. My macbook has a LED screen and the cool-white background on most pages tends to be a very bright. Great in the daytime, not so great at night… So I’ve installed the f.lux app that adjusts the screen light temperature to follow the sunset at one’s particular location, and a similar app for my OLED screen Android.
I also try and make sure to get enough real daylight in the daytime and then I dim indoor lights more and more as the evening progresses. With these simple measures, my very easily disrupted circadian rhythm has gotten markedly more normal, almost miraculously so.
From the Wikipedia LED page:
Blue pollution: Because cool-white LEDs with high color temperature emit proportionally more blue light than conventional outdoor light sources such as high-pressure sodium vapor lamps, the strong wavelength dependence of Rayleigh scattering means that cool-white LEDs can cause more light pollution than other light sources. The International Dark-Sky Association discourages using white light sources with correlated color temperature above 3,000 K.
So, no cool-white LED or metal halide streetlights please!