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High-energy visible light (HEV light) is short-wave light in the violet/blue band from 400 to 450 nm in the visible spectrum, which has a number of purported negative biological effects, namely on circadian rhythm and retinal health (blue-light hazard), which can lead to age-related macular degeneration. Increasingly, blue blocking filters are being designed into glasses to avoid blue light's purported negative effects. it is unclear whether filtering blue light with spectacles has any effect on eye health, eye strain, sleep quality or vision quality.

Blue light
Blue light refers to light in the blue part of the visible spectrum, not necessarily light that is blue, hence why the term high-energy visible (HEV) light is sometimes preferred. When HEV light is alone in a spectrum, it will appear blue, but HEV light can also be a component of broadband colors (white, purple, green, etc.). Blue light is sometimes defined broadly as having a wavelength between 400 and 525 nm, or more narrowly between 400 and 450 nm. However, the bandwidth of the blue light is not directly significant to the negative effects; rather the overlap of the light spectrum with either the blue-light hazard function or melanopsin spectral sensitivity function is a better measure of the possible negative effect of the light.

Sources of blue light
Blue light is an essential component of white light, including all forms of lighting. The color temperature of a light is a good indication of how much blue light is included, where cool light will have proportionally more blue. However, an intense warm light (e.g. direct sunlight) will still contain more blue light than a dim cool light (e.g. overcast light). LED displays, sunlight, architectural lighting, street lights, vehicle headlamps, and camera flashes all contain blue light. The distribution of light can be quantified with emission spectroscopy to create spectra, which can be analyzed to determine the extent of blue light. Another characteristic of light sources is the color rendering index (CRI), which establishes how smooth (high CRI) or peaky (low CRI) the spectrum is.

Blue LED light
Blue LEDs are often the target of blue-light research due to the increasing prevalence of LED displays and Solid-state lighting (e.g. LED illumination), as well as the blue appearance (higher color temperature) compared with traditional sources. However, natural sunlight has a relatively high spectral density of blue light, so exposure to high levels of blue light is not a new or unique phenomenon despite the relatively recent emergence of LED display technologies. While LED displays emit white by exciting all RGB LEDs, white light from lighting is generally produced by pairing a blue LED emitting primarily near 450 nm combined with a phosphor for down-conversion of some of the blue light to longer wavelengths, which then combine to form white light. This is often considered “the next generation of illumination” as SSL technology dramatically reduces energy resource requirements. One problem with blue LEDs is their peak emission wavelength of 450 nm, which is coincident with the peak of the blue-light hazard function.

Luminous efficiency
Concerns regarding blue LEDs are related to the difference between the photopic luminous flux and radiometric radiance. Photometry is concerned with the study of human perception of visible light, while radiometry is concerned with the measurement of energy. At the outer edges of the range of light perception, the amount of energy as light required to register as a perception increases. The perception of the brightness of different frequencies of light is defined according to the CIE luminosity function V(λ). The peak efficiency of light perception is defined at 555 nm, having a value of V(λ)=1. Blue LEDs, particularly those used in white LEDs, operate at around 450 nm, where V(λ)=0.038. This means that blue light at 450 nm requires more than 26 times the radiometric energy for one to perceive the same luminous flux as green light at 555 nm. For comparison, UV-A at 380 nm (V(λ)=0.000 039) requires 25 641 times the amount of radiometric energy to be perceived at the same intensity as green, three orders of magnitude greater than blue LEDs. Studies often compare animal trials using identical luminous flux rather than radiance meaning comparative levels of perceived light at different frequencies rather than total emitted energy.

Blue light hazard
Blue-light hazard is the potential for photochemically-induced retinal injury resulting from electromagnetic radiation-exposure at wavelengths primarily between 400 and 450 nm. Photochemically-induced retinal injury is caused by the absorption of light by photoreceptors in the eye. Under normal conditions, when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle.

The mechanism underlying blue-light hazard concerns a breakdown in the photochemical synergy between the retinal pigment epithelium (RPE) and the photoreceptor cells. Acute exposure takes the form of a depigmented lesion visible in the RPE, which may cause a temporary or permanent scotoma depending upon the intensity and duration of exposure. However, the specific mechanism is still largely unknown. There is some evidence that chronic exposure to blue-light increases the risk of macular degeneration.

The wavelengths of light that contribute the most to blue-light hazard are standardized as the blue-light hazard function. The function was developed by the American Council of Governmental Industrial Hygienists (ACGIH) and adopted by the Illuminating Engineering Society (IES) and International Commission on Illumination (CIE). The function peaks at 445 nm and decreases to 10% at 400 and 500nm. The reduction of the function to shorter wavelengths is due to the UV-filtering characteristic of the crystalline lens. When the lens is removed, the aphakic blue-light hazard function increases greatly in the UV.

A 2019 report by France's Agency for Food, Environmental and Occupational Health & Safety (ANSES) highlights short-term effects on the retina linked to intense exposure to blue LED light, and long-term effects linked to the onset of age-related macular degeneration. Although few studies have examined occupational causes of macular degeneration, they show that long-term sunlight exposure, specifically its blue-light component, is associated with macular degeneration in outdoor workers. However, the CIE published its position on the low risk of blue-light hazard resulting from the use of LED technology in general lighting bulbs in April 2019.

The international standard IEC 62471 assesses the photobiological safety of light sources. A proposed standard, IEC 62778, provides additional guidance in the assessment of blue-light hazard of all lighting products.

Circadian disruption
The circadian rhythm is a mechanism that regulates sleep patterns. One of the primary factors affecting the circadian ryhthm is the excitation of melanopsin, a light sensitive protein that absorbs maximally at 480 nm, but has at least 10% efficiency in the range of 450-540 nm. The periodic (daily) exposure to sunlight generally tunes the circadian rhythym to a 24-hour cycle. However, exposure to light sources that excite melanopsin in the retina during nighttime can interfere with the circadian rhythm. Harvard Health Publishing asserts that exposure to blue light at night has a strong negative effect on sleep. The aforementioned ANSES report "highlights [the] disruptive effects to biological rhythms and sleep, linked to exposure to even very low levels of blue light in the evening or at night, particularly via screens". A 2016 press release by the American Medical Association concludes that there are negative effects on the circadian rhythm from the unrestrained use of LED street lighting and white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps. However, they also indicate that street lamp brightness is more strongly correlated to sleep outcomes.

Discomfort glare
The use of LEDs in street lights and vehicle head lamps, specifically with higher color temperature (more blue light), has been correlated with higher discomfort glare.

Eye strain
Blue light has been implicated as the cause of digital eye strain, but there is no robust evidence to support this hypothesis.

Blue light blocking
Concerns over exposure to blue light has predicated several solutions to decreasing blue light exposure, including disabling or attenuating blue LEDs in displays, color shifting displays towards yellow, or wearing glasses that filter out blue light.

Digital filters
Apple's and Microsoft's operating systems and even the preset settings of standalone computer monitors include options to reduce blue-light emissions by adjusting color temperature to a warmer gamut. However, these settings dramatically reduce the size of the color gamut of the display, as they essentially simulate tritan color blindness, thereby sacrificing the usability of the displays. The filters can be set on a schedule to activate only when the sun is down.

Intraocular lenses
During cataract surgery, the opaque natural crystalline lens is replaced with a synthetic intraocular lens (IOL). The IOL may be designed to filter out equal, more or less UV light than the natural lens (have a higher or lower cutoff), and therefore attenuate or accentuate the blue-light hazard function. The effects of long term exposure of UV, violet and blue light on the retina can then be studied. However, it has been argued that IOLs that remove more blue light than natural lenses negatively affect color vision and the circadian rhythm while not offering significant photoprotection. Systematic reviews found no evidence of any effect in IOLs filtering blue light, and none provided any reliable statistical evidence to suggest any effect regarding contrast sensitivity, macular degeneration, vision, color-discrimination or sleep disturbances. One study claimed a large difference in observed fluorescein angiography examinations and observed markedly less "progression of abnormal fundus autofluorescence"; however the authors failed to discuss the fact that the excitation beam is filtered light between 465 and 490 nm, is largely blocked by blue light filtering IOLs but not clear IOLs present in the control patients.

Blue light blocking lenses
Lenses that filter blue light have been on the market for a long time in the form of brown-, orange-, and yellow-tinted sunglasses. These tinted lenses were popular for the belief that they enhanced contrast and depth perception, but after early research showing the health risks of blue light exposure, became more popular for the purported health benefits of blocking blue light.

The efficacy of blue-blocking lenses in blocking blue light is not disputed, but whether typical exposure to blue light is hazardous enough to require blue blocking lenses is highly disputed. One problem with the glasses is that they cannot achieve positive outcomes in blue-light hazard and sleep simultaneously. To be effective in against blue-light hazard, the glasses must be worn continuously, especially during the day when exposure is higher. However, to force blue-light exposure that mimics the normal daylight cycle, the glasses must only be worn at night, when the exposure is already quite low from a photoprotective perspective. Regardless, some evidence shows that lenses that block blue light may be particularly useful for people with insomnia, bipolar disorder, delayed sleep phase disorder, or ADHD, though less beneficial for healthy sleepers.

Aggressive advertisements may contribute to the incorrect public perception of the purported dangers of blue light. Even when research has shown no evidence to support the use of blue-blocking filters as a clinical treatment for digital eye strain, ophthalmic lens manufacturers continue to market them as lenses that reduce digital eye strain. Essilor claims that one may experience vision loss without their special filtering lenses, whether one requires prescription glasses or not. Zeiss offers a similar product yet does not make nearly as extreme claims. The UK's General Optical Council has criticised Boots Opticians for their unsubstantiated claims regarding their line of blue-light filtering lenses; and the Advertising Standards Authority fined them £40,000. Boots Opticians sold the lenses for a £20 markup. Trevor Warburton, speaking on behalf of the UK Association of Optometrists stated: "...current evidence does not support making claims that they prevent eye disease." In July 2022, a Gamer Advantage advert on Twitch channel BobDuckNWeave was banned by the Advertising Standards Authority for making claims that blue light glasses could improve sleep without substantiation.

Positive effects
Blue light is essential for regulating the circadian rhythm, because it stimulates melanopsin receptors in the eye. This suppresses daytime melatonin, enabling wakefulness. Working in blue-free light (aka yellow light) for long periods of time disrupts circadian patterns because there is no melatonin suppression during the day, and reduced melatonin rebound at night.

Dermatology
Blue light within the range 400-450 nm has been reported in a number of studies to be effective as local treatment of eczema and psoriasis, as it purportedly helps dampen the immune response. Recent studies have also shown improvement of facial acne upon exposure to an LED emitting at 414 nm. A combination of exposure to red and blue lights is used more and more in clinical dermatologic therapies. Constructors such as Philips currently develop devices and techniques emitting in the blue visible spectrum to be used in dermatologic therapy.