Blue light

Biological effects of high-energy visible light

High-energy visible light (HEV light) or blue light is high-frequency, high-energy light in the violet/blue band from 400 to 450 nm in the visible spectrum, which has a number of biological effects, including those on the eye.

Blue light is a range of the visible light spectrum, defined as having a wavelength between 400 and 525  nm, and includes wavelengths between violet and cyan in the spectrum. 

Blue light, a type of high-energy light, is part of the visible light spectrum.

Blue LED light sources are becoming increasingly common.

Blue light may be a cause of age-related macular degeneration.

Some sunglasses and beauty creams specifically block HEV.

There is an adverse effect of blue LED light (400-450 nm spike) on the eye, which can lead to impaired vision. 

Short-term effects of LED blue light on the retina are linked to its intense exposure, and long-term effects linked to the onset of age-related macular degeneration.

Long-term sunlight exposure, specifically its blue-light component, is associated with macular degeneration in outdoor workers.

Exposure to blue light, especially blue LED light, but also broad-spectrum blue light, at night, has a stronger negative effect on sleep.

There are also negative health impacts from the unrestrained use of LED street lighting.

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.

Blue LED light or short-wavelength LED, also called  narrow spectrum blue light, is a type of high-energy visible light, defined as having a wavelength between 400 and 450  nm. 

This light is common in LEDs.

Blue light is an essential component of white light. 

White can be made from either narrow-spectrum or broad-spectrum blue. 

LED technology tends to combine narrow-spectrum blue and yellow, while other technologies include more cyan and red. 

Fluorescent light generates violet and cyan spikes, in addition to having a smaller narrow-spectrum blue component. 

Natural light has a much more even distribution of blue wavelengths than most artificial light.

Exposure to blue light comes from computers, televisions, and lights. 

Much of the harmful exposure arises from light-emitting diodes (LEDs). 

Many white LEDs are produced by pairing a blue LED with a lower-energy phosphor, thereby creating solid-state light (SSL). 

SSL technology dramatically reduces energy resource requirements.

There is an increased exposed to blue LED light via everyday technology smartphones, computers, videos, etc.

Younger individuals use high rates of blue light technologies. 

Blue-light hazard related to potential,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. 

 Normally, when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle.

At wavelengths of blue light below 430 nm this greatly increases the potential for oxidative damage.

For blue-light circadian therapy, harm is minimized by employing blue light at the near-green end of the blue spectrum. 

1-2 min of 408 nm and 25 minutes of 430 nm are sufficient to cause irreversible death of photoreceptors and lesions of the retinal pigment epithelium. 

The action spectrum of light-sensitive retinal ganglion cells was found to peak at approximately 450 nm.

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.[21][22] 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.[23][24] 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.[25][26] As interest in LED backlighting has increased, so has the technology developed. Studies often select low-quality generic LEDs from little-known brands with a high proportion of blue light, especially selecting low CRI LEDs which are not suitable for either lighting or backlight technologies. LCD screens and LED lighting generally use much higher CRI LEDs as consumers demand accurate color reproduction.[27][28][21] White LEDs are designed to emulate natural sunlight as closely as is economically and technologically possible. Natural sunlight has a relatively high spectral density of blue light making exposure to relatively high levels of blue light not a new or unique phenomenon despite the relatively recent emergence of LED display technologies.

Much of this marketing fails to distinguish between the sharp, 400-450 nm blue spike in mainstream LED bulbs, versus the broad-spectrum blue (up to 525 nm cyan) present in other lighting technologies (including pre-LED technologies, and very new, cyan-rich LED technologies that go beyond the older CRI metrics), and natural light.

Broad-spectrum blue light, including cyan wavelengths, such as in natural light or most fluorescent lights, is essential to wakefulness, because it stimulates melanopsin receptors in the eye.

This suppresses daytime melatonin, enabling wakefulness. 

Working in blue-free light for long periods of time disrupts circadian patterns because there is no melatonin suppression during the day, and reduced melatonin rebound at night.

Blue light within the range 400-450 nm has been reported to be effective as local treatment of eczema and psoriasis, as it purportedly helps dampen the immune response.

Blue light improves facial acne upon exposure to a LED emitting at 414 nm.

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