The Science of Blue Light Hazards: Retinal Impact and Road Safety Analysis

Blue Light Hazards

The Science Behind the Screen

The optical pathway in a human eye is connected to the visual cortex (part of the brain that mediates the sense of sight) via the nervous system. The nervous system comprises photoreceptors of two types: 1) Rods; 2) Cones (named based on the shapes of these nerve receptors). These photoreceptors, in turn, contribute to three types of vision with image-forming functions and are important for normal daily function and life quality.

Scotopic (Rod) Vision

When the field luminances lie between 10⁻⁶ cd/sq. m and 10⁻² cd/sq. m. This is a vision in the darkness. The world is grey, and there is no sensation of colour.

Mesopic Vision

Most important vision from a lighting designer's point of view. This

occurs when the field luminance is raised upwards from 10⁻² cd/sq m to 10⁻¹ cd/sq m. As the luminance moves, the luminosity of red increases upward more strongly than that of the blues due to changing contributions of the rods and cone receptors. This is known as the Purkinje phenomenon and is considered an important aspect for designing effective road lighting, as it takes into account the luminance concept as well as the neurological aspects of road lighting.

Photopic (Cone) Vision

This is a daylight vision, i.e., when the luminance is above 10 cd/sq m. Photopic vision is coloured.

ipRGCs photoreceptors

A third type of photoreceptor was discovered (first in mice in 2002) and then in humans and primates in 2005. These receptors were found in the mammalian retina and are called Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs). Melanopsin, a photopigment in the opsin family (light-sensitive retinal proteins), was found to form a meshwork within ipRGCs. These photo-receptors were found to be sensitive to the absorption of short-wavelength blue in the visible region, peaking at around 480 nm (deep blue). Unlike the classical photoreceptors, rods & cones, which contribute to image formation, ipRGCs are non-image-forming. These cells contribute to subconscious non-image functions. They serve as primary conduits through which photic information is relayed from the retina to non-image-forming visual centres of the brain, i.e., direct communication to the circadian system, which impacts mental and physical he­­­­­­­­­alth.­­­­ Extensive studies show that blue light, after passing through our cornea and lens, excites the melanopsin in ipRGCs with absorption sensitivity peaking at 482 nm (deep blue region). Photo-reversal of bleaching (found to be most effective with blue light) takes place if the duration of exposure to this wavelength is either excessive or subject to shorter exposures over prolonged periods. It is a photochemical reaction which augments the capability of rhodopsin molecules (photopigments contained in the rods) to absorb photons in large numbers. This may lead to a cascading effect, allowing the molecules to reach the critical number of photons required to induce damage in the retinal cells. In view of the crystalline nature of the lens in infants and children, the penetration of blue light is high. Thus, this type of retinal damage is more pronounced in infants and children.

Digital devices such as smartphones, iPads, e-readers (kindles), and LED lights did not exist a decade ago. Over the last five years or so, there has been a galloping increase in the use of these devices. LED, which contains about 35% of harmful blue light, has nowadays become a dominant technology for backlighting in all digital devices. But what is more disturbing is the gradual replacement of traditional light sources by more energy-efficient LED sources.

Pro-Tip for Digital Users: While reducing screen time is best, high-quality blue light blocking filters can mitigate immediate strain.

Browse Blue Light Blocking Screen Protectors

Driving Hazards

After the discovery of the blue LED at the end of the twentieth century, extensive research started in order to commercialise the use of LEDs so that it can be used for general lighting. The first step was to get white light, which was made possible by the use of yellow phosphors. Despite great developments in phosphor technology, it has been observed that over a course of time, bleaching of phosphors (particularly in high-power LEDs) causes a shift in colour temperature. The blue light is not absorbed as effectively, and, in turn, the blue light increases over time. Of late, the city of Calcutta (Kolkata) has witnessed an invasion of LED lights in the public domain. Change to a new concept is good, but not at the cost of standard norms of good lighting practice. Here, almost all streetlight poles and guard rails of flyovers are getting adorned with blue and white strips of LED. The blue is deep, i.e., in the shorter wavelength. As a driver, I have experienced the distracting and painful nature of driving through a maze of white and blue (mostly long stretches of blue) on Calcutta’s longest flyover from Race Course to Parama Island at Eastern Metropolitan Bypass. It is not only distracting; it gobbles the traditional streetlights on the flyover on which a motorist needs to focus for safe driving. To add to the woes, most of the strips are deep blue, which adversely affects the ocular health of drivers frequenting such stretches.

Relative spectral sensitivity of the human eye. The left-hand curve is for the dark-adapted eye, and the right-hand curve is for the light-adapted eye.

Intensity distribution curve for white LED

Poles on a Calcutta flyover wrapped with blue and white LED strip lights

Guard rail on a Calcutta flyover decorated with a blue LED strip

This photograph, taken from the front seat of a moving vehicle, shows how confusing it appears to a driver.

References: 

• Melanospin: A photopigment regulatory Cicadian Photoentrainment may lead to a blue-light-induced treatment of diabetes (Anamika Sengupta, Ross University School of Medicine)
• Effects of blue light on the circadian system and eye physiology Gianluca Tosini,¹ Ian Ferguson,² and Kazuo Tsubota
• Lamps & Lighting - Henderson & Marsden
• The importance of intrinsically photosensitive retinal ganglion cells  for lighting design - Dingcai Cao and Pablo A. Barrionuevo
  

 

---

Disclosure: As an Amazon Associate, I earn from qualifying purchases made through links in this post. This helps support the technical research and travel tales shared here.

Note: Product recommendations are based on technical merit. As an Amazon Associate, I may earn a commission from qualifying purchases at no extra cost to you.