How do LEDs affect vision?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

The article discusses the conditions for the formation of an excess dose of blue light under LED lighting. It is shown that the assessments of photobiological safety, carried out in accordance with GOST R IEC 62471-2013, need to be clarified taking into account the change in the diameters of the pupil of the eye under LED lighting and the spatial distribution of the light-absorbing blue light (460 nm) pigment in the macula of the retina.

The methodological principles of calculating the excess dose of blue light in the spectrum of LED lighting in relation to sunlight are presented. It is indicated that today in the United States and Japan the concept of LED lighting is changing and white light LEDs are being created to minimize the risks of human health damage. In the United States in particular, this concept extends not only to general lighting, but also to computer monitors and car headlights.

Nowadays, LED lighting is being introduced more and more in schools, kindergartens and medical institutions. To assess the photobiological safety of LED luminaires, GOST R IEC 62471-2013 “Lamps and lamp systems. Photobiological safety ". It was prepared by the State Unitary Enterprise of the Republic of Mordovia “Scientific Research Institute of Light Sources named after A. N. Lodygin "(State Unitary Enterprise of the Republic of Mordovia NIIIS named after A. N. Lodygin") on the basis of its own authentic translation into Russian of the international standard IEC 62471: 2006 "Photobiological safety of lamps and lamp systems" (IEC 62471: 2006 "Photobiological safety of lamps and lamp systems ") and is identical to it (see clause 4. GOST R IEC 62471-2013).

Such a transfer of the standard implementation suggests that Russia does not have its own professional school for photobiological safety. The assessment of photobiological safety is extremely important for ensuring the safety of children (generation) and reducing threats to national security.

Comparative analysis of solar and artificial lighting

The assessment of the photobiological safety of a light source is based on the theory of risks and a methodology for quantifying the limit values of exposure to hazardous blue light on the retina. The limit values of the indicators of photobiological safety are calculated for the specified limit of irradiation with a pupil diameter of 3 mm (pupil area 7 mm2). For these values of the eye pupil diameter, the values of the function B (λ) are determined - the weighted spectral hazard function from blue light, the maximum of which falls on the spectral radiation range of 435-440 nm.

The theory of risks of negative effects of light and the methodology for calculating photobiological safety was developed on the basis of the fundamental articles of the founder of photobiological safety of artificial light sources, Dr. David H. Sliney.

David H. Sliney has for many years served as Division Chief of the US Army's Center for Health Promotion and Preventive Medicine and has led photobiological safety projects. In 2007, he completed his service and retired. His research interests focus on subjects related to UV exposure to the eyes, laser radiation and tissue interactions, laser hazards, and the use of lasers in medicine and surgery. David Sleeney has served as a member, consultant and chairman of numerous commissions and institutions that have developed safety standards for protection against non-ionizing radiation, in particular lasers and other high-intensity optical radiation sources (ANSI, ISO, ACGIH, IEC, WHO, NCRP, and ICNIRP). He co-authored The Safety Handbook with Lasers and Other Optical Sources, New York, 1980. From 2008-2009, Dr. David Sleeney served as President of the American Society of Photobiology.

The fundamental principles developed by David Sleeney underlie the modern methodology for the photobiological safety of artificial light sources. This methodological pattern is automatically transferred to LED light sources. It has raised a large galaxy of followers and students who continue to extend this methodology to LED lighting. In their writings, they try to justify and promote LED lighting through the classification of risks.

Their work is supported by Philips-Lumileds, Osram, Cree, Nichia and other LED lighting manufacturers. Currently, the field of intensive research and analysis of the possibilities (and limitations) in the field of LED lighting involves:

• government agencies such as the US Department of Energy, RF Ministry of Energy;

• public organizations such as the Illuminating Engineering Society of North America (IESNA), Alliance for Solid-State Illumination and Technologies (ASSIST), International Dark-Sky Assosiation (IDA) and NP PSS RF;

• the largest manufacturers Philips-Lumileds, Osram, Cree, Nichia and

Russian manufacturers Optogan, Svetlana Optoelectronica;

• as well as a number of research institutes, universities, laboratories: Lighting Research Center at Rensselaer Polytechnic Institute (LRC RPI), National Institute of Standards and Technology (NIST), American National Standard Institute (ANSI), as well as NIIIS im. AN Lodygina , VNISI them. S. I. Vavilov.

From the point of view of determining an excess dose of blue light, the work "Optical safety LED lighting" (CELMA-ELC LED WG (SM) 011_ELC CELMA position paper optical safety LED lighting_Final_July2011) is of interest. This European report compares the spectra of sunlight with artificial light sources (incandescent, fluorescent and LED lamps) in accordance with the requirement of EN 62471. Through the prism of the modern paradigm of hygienic assessment, consider the data presented in this European report in order to determine the excess proportion of blue light in the spectrum of the LED white light source. In fig. 1 shows the spectral pattern of a white light LED, which consists of a crystal emitting blue light and a yellow phosphor with which it is coated to produce white light.

In fig. 1. Also indicated are the reference points to which the hygienist should pay attention when analyzing the spectrum of light from any source. From this point of view, consider the spectra of sunlight (Fig. 2).

The figure shows that in the range of color temperature from 4000 K to 6500 K, the conditions of the "melanopsin cross" are observed. On the energy spectrum of light, the amplitude (A) at 480 nm must always be greater than the amplitude at 460 nm and 450 nm.

At the same time, the dose of blue light 460 nm in the spectrum of sunlight with a color temperature of 6500 K is 40% higher than that of sunlight with a color temperature of 4000 K.

The effect of the "melanopsin cross" is clearly visible from a comparison of the spectra of incandescent lamps and LED lamps with a color temperature of 3000 K (Fig. 3).

The excess proportion of blue light in the spectrum of the LED spectrum in relation to the proportion of blue light in the spectrum of an incandescent lamp exceeds more than 55%.

Considering the above, let's compare sunlight at Tc = 6500 K (6500 K is the limiting color temperature for the retina according to David Sleaney, and according to sanitary standards it is less than 6000 K) with the spectrum of an incandescent lamp Tc = 2700 K and the spectrum of an LED lamp with Tc = 4200 K at an illumination level of 500 lux. (fig. 4).

The figure shows the following:

- LED lamp (Tc = 4200 K) has an emission of 460 nm more than sunlight (6500 K);

- in the light spectrum of an LED lamp (Tc = 4200 K), the dip at 480 nm is an order of magnitude (10 times) greater than in the spectrum of sunlight (6500 K);

- in the light spectrum of an LED lamp (Tc = 4200 K), the dip is 480 nm several times greater than in the light spectrum of an incandescent lamp (Tc = 2700 K).

It is known that under LED illumination, the diameter of the pupil of the eye exceeds the limit values - 3 mm (area 7 mm2) according to GOST R IEC 62471-2013 “Lamps and lamp systems. Photobiological safety.

From the data shown in Fig. 2, it can be seen that the dose of 460 nm blue light in the spectrum of sunlight for a color temperature of 4000 K is much less than the dose of 460 nm blue light in the spectrum of sunlight at a color temperature of 6500 K.

It follows from this that the dose of 460 nm blue light in the spectrum of LED lighting with a color temperature of 4200 K will significantly (by 40%) exceed the dose of 460 nm blue light in the spectrum of sunlight with a color temperature of 4000 K at the same illumination level.

This difference between doses is the excess dose of blue light under LED lighting relative to sunlight with the same color temperature and a given level of illumination. But this dose should be supplemented by a dose of blue light from the effect of inadequate control of the pupil under LED lighting conditions, taking into account the uneven distribution of pigments that absorb 460 nm blue light in volume and area. It is an excessive dose of blue light that leads to an acceleration of degradation processes that increase the risks of early visual impairment in comparison with sunlight, all other things being equal (a given level of illumination, color temperature and effective work of the macular retina, etc.)

Physiological features of the structure of the eye, affecting the safe perception of light

The retinal protection circuitry was formed in sunlight. With the spectrum of sunlight, there is adequate control of the diameter of the pupil of the eye to close, which leads to a decrease in the dose of sunlight reaching the cells of the retina. The diameter of the pupil in an adult varies from 1.5 to 8 mm, which provides a change in the intensity of the light incident on the retina by about 30 times.

A decrease in the diameter of the pupil of the eye leads to a decrease in the area of the light projection of the image, which does not exceed the area of the "yellow spot" in the center of the retina. The retinal cells are protected from blue light by the macular pigment (with an absorption maximum of 460 nm) and the formation of which has its own evolutionary history.

In newborns, the area of the macula is light yellow with indistinct contours.

From three months of age, a macular reflex appears and the intensity of the yellow color decreases.

By one year, the foveolar reflex is determined, the center becomes darker.

By the age of three to five years, the yellowish tone of the macular area almost merges with the pink or red tone of the central retinal area.

The macular area in children 7-10 years of age and older, as in adults, is determined by the avascular central retinal area and light reflexes. The concept of "macular spot" arose as a result of macroscopic examination of cadaveric eyes. On planar preparations of the retina, a small yellow spot is visible. For a long time, the chemical composition of the pigment that stains this area of the retina was unknown.

Currently, two pigments have been isolated - lutein and the lutein isomer zeaxanthin, which are called macular pigment, or macular pigment. The level of lutein is higher in the places with a higher concentration of rods, the level of zeaxanthin is in the places with a higher concentration of cones. Lutein and zeaxanthin belong to the carotenoid family, a group of natural plant pigments. Lutein is believed to have two important functions: first, it absorbs blue light that is harmful to the eyes; secondly, it is an antioxidant, blocks and removes reactive oxygen species formed under the influence of light. The content of lutein and zeaxanthin in the macula is unevenly distributed over the area (maximum in the center, and several times less at the edges), which means the protection against blue light (460 nm) is minimal at the edges. With age, the amount of pigments decreases, they are not synthesized in the body, they can only be obtained from food, so the overall effectiveness of protection from blue light in the center of the macula depends on the quality of nutrition.

The effect of inadequate pupil control

In fig. 5. is a general scheme for comparing the projections of the light spot of a halogen lamp (the spectrum is close to the solar spectrum) and an LED lamp. With LED light, the illumination area is larger than with a halogen lamp.

The difference in the allocated areas of illumination is used to calculate an additional dose of blue light from the effect of inadequate control of the pupil under LED lighting conditions, taking into account the uneven distribution of pigments that absorb 460 nm blue light in volume and area. This qualitative assessment of the excess proportion of blue light in the spectrum of white LEDs can become a methodological basis for quantitative assessments in the future. Although from this it is clear the technical decision on the need to fill the gap in the region of 480 nm to the level of elimination of the effect of "melanopsin cross". This solution was formalized in the form of an inventor's certificate (LED white light source with a combined remote photoluminescent convector. Patent No. 2502917 dated 2011-30-12.). This ensures Russia's priority in the field of creating LED white light sources with a biologically adequate spectrum.

Unfortunately, the experts of the Ministry of Industry and Trade of the Russian Federation do not welcome this direction, which is the reason not to finance work in this direction, which concerns not only general lighting (schools, maternity hospitals, etc.), but also the backlighting of monitors and car headlights.

With LED lighting, inadequate control of the diameter of the pupil of the eye occurs, which creates conditions for obtaining an excess dose of blue light, which negatively affects the cells of the retina (ganglion cells) and its vessels. The negative effect of an excess dose of blue light on these structures was confirmed by the works of the Institute of Biochemical Physics. N. M. Emanuel RAS and FANO.

The above-identified effects of inadequate control of the eye pupil diameter apply to fluorescent and energy-saving lamps (Fig. 6). At the same time, there is an increased proportion of UV light at 435 nm ("Optical safety of LED lighting" CELMA ‐ ELC LED WG (SM) 011_ELC CELMA position paper optical safety LED lighting_Final_July2011)).

In the course of experiments and measurements carried out in US schools, as well as in Russian schools (Research Institute of Hygiene and Health Protection of Children and Adolescents, SCCH RAMS), it was found that with a decrease in the correlated color temperature of artificial light sources, the diameter of the pupil of the eye increases, which creates the preconditions for a negative exposure to blue light on cells and blood vessels of the retina. With an increase in the correlated color temperature of artificial light sources, the diameter of the pupil of the eye decreases, but does not reach the values of the diameter of the pupil in sunlight.

An excessive dose of UV blue light leads to an acceleration of degradation processes that increase the risks of early visual impairment compared to sunlight, all other things being equal.

An increased dose of blue in the spectrum of LED lighting affects human health and the functioning of the visual analyzer, which increases the risks of disability in vision and health at working age.

The concept of creating semiconductor light sources with biologically adequate light

In contrast to the conservatism of experts from the Ministry of Industry and Trade of the Russian Federation and the Skolkovo Innovation Center, the concept of creating semiconductor white light sources with biologically adequate light cultivated by the authors of the article is gaining a supporter all over the world. For example, in Japan, Toshiba Material Co., LTD has created LEDs using TRI-R technology (Fig. 7).

Such a combination of violet crystals and phosphors allows to synthesize LEDs with spectra close to the spectrum of sunlight with different color temperatures, and to eliminate the above deficiencies in the LED spectrum (blue crystal coated with yellow phosphor).

In fig. eight.presents a comparison of the spectrum of sunlight (TK = 6500 K) with the spectra of LEDs using TRI-R technology and technology (blue crystal coated with yellow phosphor).

From the analysis of the presented data, it can be seen that in the white light spectrum of LEDs using TRI-R technology, the gap at 480 nm is eliminated and there is no excess blue dose.

So, conducting research to identify the mechanisms of the effect of light of a certain spectrum on human health is a state task. Ignoring these mechanisms leads to billions of dollars in costs.

conclusions

The Sanitary Rules record norms from lighting technical normative documents, by translating European standards. These standards are formed by specialists who are not always independent and carry out their own national technical policy (national business), which often does not coincide with the national technical policy of Russia.

With LED lighting, inadequate control of the eye pupil diameter occurs, which casts doubt on the correctness of photobiological assessments according to GOST R IEC 62471-2013.

The state does not finance advanced research on the impact of technology on human health, which is why hygienists are forced to adapt the norms and requirements to the technologies that are being promoted by the transfer technology business.

Technical solutions for the development of LED lamps and PC screens should take into account ensuring the safety of eyes and human health, take measures to eliminate the effect of the "melanopsin cross", which occurs for all currently existing energy-saving light sources and backlighting of information display devices.

Under LED illumination with white LEDs (blue crystal and yellow phosphor), which have a gap in the spectrum at 480 nm, there is inadequate control of the eye pupil diameter.

For maternity hospitals, childcare facilities and schools, lamps with a biologically adequate spectrum of light, taking into account the characteristics of children's vision, should be developed and undergo mandatory hygienic certification.

Conclusions briefly from the editor:

1. LEDs emit very brightly in blue and near UV regions and very weakly in blue.

2. The eye "measures" the brightness in order to narrow the pupil by the level of not blue, but blue color, which is practically absent in the spectrum of a white LED, therefore, the eye "thinks" that it is dark and opens the pupil wider, which leads to the fact that the retina receives many times more light (blue and UV) than when illuminated by the sun, and this light "burns out" the light-sensitive cells of the eye.

3. In this case, an excess of blue light in the eye leads to a deterioration in the clarity of the image. a picture with a halo is formed on the retina.

4. The eye of children is about an order of magnitude more transparent to blue than that of the elderly, therefore, the process of "burning out" in children is many times more intense.

5. And do not forget that LEDs are not only lighting, but now almost all screens.

If we give one more image, then eye damage from LEDs is akin to blindness in the mountains, which occurs from the reflection of UV from snow and is more dangerous just in cloudy weather.

The question arises, what to do for those who already have LED lighting, as usual, from LEDs of unknown origin?

Two options come to mind:

1. Add additional blue light (480nm) illumination.

2. Put a yellow filter on the lamps.

I like the first option more, because there are on sale blue (light blue) LED strips with 475nm radiation. How to check what wavelength is there in reality?

The second option will "eat" part of the light and the lamp will be dimmer, and, moreover, it is also not known what part of the blue we will remove.