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ISSN : 1229-6457(Print)
ISSN : 2466-040X(Online)

The Korean Journal of Vision Science Vol.21 No.4 pp.565-573
DOI : https://doi.org/10.17337/JMBI.2019.21.4.565

Qualitative and Quantitative Analysis of Blue Light Blocking Effect

Seo-Hee Lee¹⁾

, Ji-Yoon Kim¹⁾

, Jeong-Min Im¹⁾

, Hye-won Kim¹⁾

, Su-Bin Sung¹⁾

, Hyo-Jeong Yoon¹⁾

, Min-Su Kim¹⁾

, Suk-Ho Cho¹⁾

, Young-Chul Kim²⁾*

¹⁾Dept. of Optometry, Eulji University, Student, Seong-nam
²⁾Dept. of Optometry, Eulji University, Professor, Seong-nam

Address reprint requests to Young-Chul Kim Dept. of Optometry, Eulji University, Seongnam TEL: +82-31-740-7201, E-mail: yckim@eulji.ac.kr

Received November 15, 2019 Review December 24, 2019 Accepted December 24, 2019

Abstract

Purpose :

A new method of quantitatively analyzing the effects of blue light blocking lenses was proposed and applied to a commercially available functional lens.

Methods :

The light transmittance of the lens was measured and qualitative analysis of the efficiency was performed by applying the blue light blocking efficiency function. In addition, a new quantitative analysis method for integrating and quantifying blue light blocking efficiency results was introduced, and applied to commercially available blue light blocking functional lenses for comparative analysis.

Results :

As a result of applying qualitative analysis method to general lens, two lenses manufactured by coating method and one lens manufactured by coloring method, all lenses were found to have excellent effect of blocking light in short wavelength region. However, the results of the quantitative analysis method confirmed that there is a slight difference for each lens.

Conclusion :

As the optical characteristics of various display devices and smartphones are evolving and changing day by day, optical characteristics analysis of light sources and optical products is required in various ways. Accordingly, the new quantitative analysis method introduced in this study was confirmed to be an effective means.

Key Words : Blue light , Blue-light blocking lens , Hazard function

청광차단효과의 정성적, 정량적 분석

이 서희¹⁾, 김 지윤¹⁾, 임 정민¹⁾, 김 혜원¹⁾, 성 수빈¹⁾, 윤 효정¹⁾, 김 민수¹⁾, 조 석호¹⁾, 김 영철²⁾*

¹⁾을지대학교, 안경광학과 학생
²⁾을지대학교, 안경광학과 교수

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Ⅰ. Introduction

We are affected by the light emitted by various light sources, including sunlight. The sun has a surface temperature of approximately 6,500 K. The electromagnetic waves emitted by the sun range from very short ultraviolet to visible and infrared light. Although the intensity of visible light is the strongest, ultraviolet rays, which have a great effect on the human body, are contained. In addition, our eyes are affected by electromagnetic waves emitted from various light sources such as TVs, monitors and smartphones in addition to natural light such as sunlight.

For this reason, in recent years, interest by blue light which has a big influence on eyes is increasing. Blue light refers to electromagnetic waves of approximately 380 to 550 nm, which is more energyintensive than the long-wave electromagnetic waves.

Prolonged exposure to strong ultraviolet light emitted by the sun can cause burns to the cornea or conjunctiva, and damage the lens and retinal cells. Ultraviolet B can penetrate the ocular surface and ultraviolet A can penetrate into the eye, causing eye diseases such as keratitis, cataracts, and macular degeneration. In addition, as the use of display devices such as smartphones and PC monitors is increasing in recent years, the time and frequency of exposure to harmful blue light are increasing. Blue light is a wavelength of 380~500 nm of visible light, which can cause eye fatigue, dry eye, decreased vision, and damage the retina and lens of the eye.

As a result, previous studies on the effects of blue light have been published. Prolonged exposure to blue light has been shown to inhibit sleepinducing hormone melatonin, which interferes with sleep.^1-3) Long-term exposure to blue light has also been reported to induce the production of toxic free radicals, which can damage visual cells, and induce lacrimal gland dysfunction, resulting in reduced water production, leading to dry eye syndrome.^4-9)

In order to solve this problem, a blue light blocking lens is commercially available. Blue light blocking lenses can be classified into coating and coloring depending on the manufacturing method. This study focused on whether there is a difference in light blocking effect according to the manufacturing method of the blue light blocking lens, and how the difference in blocking effect compared to a general lens. To this end, we introduced a technique to quantify the blocking efficiency and applied it to the lens to be analyzed for comparative analysis.

Fig. 1 shows four lenses used in the analysis, one common lens and three light-blocking functional lenses(two coated and one tinted). One normal lens and three functional lenses have a refractive index of 1.6 and a vertex refractive power of 0 diopter, both commercially available and manufactured by the same company.

Ⅱ. Materials and Methods

In this study, the light transmittance of each lens was compared by spectral analysis. The light transmittance is measured using a Spectral Transmittance Meter(TM-1, TOPCON, Tokyo, JAPAN). The light source used here is D65, which has a light intensity distribution similar to daytime natural light. The light source D65 is important because D65 is widely used in various fields such as digital art, film, photography, and optical property analysis.

Fig. 2(a) shows the light intensity distribution by wavelength of incident light used for the light transmittance analysis. The equipment used in this study is represented by normalized light intensity for all wavelengths, as shown in Fig. 2(b). Accordingly, the light transmittance of the lens to be analyzed is represented as a relative intensity ratio with respect to the intensity of incident light.

Fig. 3 shows the light transmittance by the lens used in this study. Fig. 3(a) shows the light transmittance measured as a percentage. The light transmittance of the wavelength up to 400 nm is almost 0%, so that the near-ultraviolet and violet light are effectively blocked by all lenses(general lens, functional lens A, B, C).

Fig. 3(b) shows the relative intensity distribution of incident light for each wavelength of light that passes through the lens. Compared with Fig. 2(a), which is the light intensity distribution of incident light, the intensity is significantly decreased in the short wavelength region, but the long wavelength region is almost unchanged. This is because the light transmittance of the long wavelength region in Fig. 3(a) is close to one.

The area under the graph was examined to quantitatively analyze the blocking effect. For this purpose, the spectral intensities of the incident light and the light passing through the lens were compared. Fig. 4(a) shows the intensity distribution transmitted through the target lens including incident light. Comparing the incident light and the transmitted light intensity of the lens, there is a marked difference in the short wavelength region of 500 nm or less.

However, at higher wavelengths, there is no similar difference and similar distribution. Therefore, it can be confirmed that the blocking effect of the short wavelength is obvious in all lenses including the general lens. However, it is difficult to judge the superiority of the effect of each functional lens by comparing the transmittance distribution.

Fig. 4(b) shows the light intensity distribution of incident light and lens C. The shaded area below shows the area of light intensity distribution of light passing through lens C for quantitative analysis. This is to introduce a new analysis method because it was determined that the distribution of the intensity of each wavelength has a limitation in analyzing the lens effect. That is, the transmittance may be high in some wavelength regions and low in other wavelength regions, depending on the lens.

Therefore, we quantified the area under the graph to analyze the blocking effect from a new perspective. Fig. 4(c) shows the values obtained by integrating the area under (b). The black point is the integral value for the entire region of visible light and the bottom red point is the integral value of the short wavelength region of 550 nm or less. In both cases, the area of the blue light blocking lens of the lens C has the minimum value. Therefore, as shown in Fig. 4(a), the transmitted light intensity distribution in the long wavelength region has almost the same value, so it can be determined that the lens C has the best blue light blocking effect.

It is important to note that the results of this study are limited to some of the lenses used in the analysis. However, it can be seen that the graph area ratio comparison method along with the transmitted light intensity distribution can provide a new method for analyzing blue light blocking effects, as in this study.

Ⅲ. Results

Blue light risk generally refers to photo-chemical risks to the retinal tissue of the eye in relation to exposure to the sun or bright light sources. The risk of photo-chemical damage depends on the wavelength, peaking in the blue portion of the optical spectrum from about 435 nm to 440 nm.

1. Blue light blocking rate

In this study, the optical properties of blue light around 400nm were analyzed. Fig. 5 shows the light blocking rate of the lens used in this study. The blocking rate for short wavelengths below 400nm was over 90 %, indicating that the blue light blocking efficiency of all lenses used in the analysis was very high.

2. Blue light blocking efficiency

The effect of blue light on the retina depends on the wavelength. The numerical value according to the wavelength is called the blue light hazard function. Fig. 6(a) shows the blue light hazard function for each wavelength. The risk index of wavelengths 435 nm and 440 nm is the largest and is 1, and the function has a smaller value at the other wavelengths.^10-15)

Fig. 6(b) shows the blue light blocking efficiency results obtained by reflecting the blue hazard function in the values in Fig. 5. The distribution is very different from that in Fig. 5. Lens A had the highest blocking efficiency at 420 nm but showed a sharp decrease. Lens B and lens C, on the other hand, had a similar distribution. The highest blocking efficiency was observed at 420 nm and gradually decreased. However, lens C showed the highest blocking efficiency overall. Thus, among the four lenses used in this study, when the lens C reflected the hazard function, the blue light blocking effect was found to be the best. However, it is difficult to judge the superiority of the lens A which performs well in some wavelengths and the lens C which performs well in a wide range.

In the case of the non-functional ordinary lens (lens A), Fig. 5 shows a similar distribution to other functional lenses. However, when the risk function was reflected, the blocking efficiency was found to be somewhat lower. Therefore, it can be determined that the blue light blocking effect of the functional lens is high.

3. Quantitative analysis of blue light blocking efficiency

In the previous section, we qualitatively analyzed Fig. 6(b), the result of blue light blocking efficiency. Now, we will compare the efficiency through quantitative analysis. Fig. 7(a) shows the area under the blue light blocking efficiency graph for lens C. This area was integrated to quantitatively compare blue light blocking efficiency for the lenses used in this study by using the ORIGN Version 9.0(OriginLab, Co., USA) Fig. 7(b) shows the integral of the bottom area of the blue light blocking efficiency in Fig. 6(b) of each lens.

The integral values of the original lens and lenses A, B, and C were calculated to be 6.36, 12.72, 14.66, and 19.53, respectively. Therefore, blue light blocking efficiency of lens C was the highest. The blue light blocking efficiency of the functional lenses A, B, and C was 2.00, 2.30, and 3.07, respectively, compared to the general lenses. Lens C is also 1.53 and 1.33 times larger than lenses A and B, respectively. That is, the blue light blocking effect can be evaluated as the best. Although the effect of the functional lens can be evaluated by the blue light transmittance and the blue light blocking efficiency, it is judged that various effects can be analyzed by adding the quantitative analysis in this study.

Ⅳ. Discussion and Conclusion

Since modern people are exposed to not only natural light but also display devices and smartphones for a long time, the risk factors for eye health are increasing day by day. Therefore, it is very important to analyze the optical characteristics of various visual devices and to accurately diagnose the effects on the eyes.

In this study, the optical characteristics of the blue light blocking functional lens were analyzed and compared with those of the general lens. To this end, optical characteristics of the blue light blocking functional lens of the two lenses manufactured by the coating method and the one manufactured by the coloring method were analyzed.

Both normal and three functional lenses block short wavelength light below 400 nm, and the blocking rate is more than 90 %. In the analysis using the blue light hazard function, all three functional lenses showed the highest blue light blocking efficiency at 420 nm, and the lens manufactured by the coating method showed the highest as 40 % or more. On the other hand, for light up to 450 nm, the blue light blocking efficiency of the lens manufactured by the coloring method was analyzed to be the best.

The results of comparative analysis of blue light blocking efficiency by quantitative analysis showed more clear differences. The three functional lenses showed higher blocking efficiency than normal lenses, and the analysis method by the integration confirmed the possibility of providing a new criterion. Here, we would like to emphasize that the efficiency analysis method has been newly introduced as a political analysis method rather than defining the advantage of the blue light blocking efficiency of each lens used in the analysis. Accordingly, based on various analysis results, if a light blocking lens having higher efficiency can be manufactured, it is expected to contribute to eye health.

Figure

Fig. 1.

(a) Original lens (b) Coating lens (Lens A) (c) Coated lens (Lens B) (d) Tinted lens (Lens C).

Fig. 2.

Spectral intensity distribution (a) Relative power (b) Normalized intensity.

Fig. 3.

(a) Light transmittance (b) Transmitted light relative power.

Fig. 4.

Transmitted light relative power with incident light (b) Relative power for integration area (c) Integration area.

Fig. 5.

Blue light blocking ratio.

Fig. 6.

(a) Blue light hazard function (b) Blue light blocking efficiency.

Fig. 7.

(a) Blue light blocking efficiency (b) Integration area.

Table

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