Change of blue light hazard and circadian effect of LED backlight displayer with color temperature and age

Yang Chaopu; Fang Wenqing; Tang Jiancheng; Yang Fan; Liu Yanfeng; Li Chun

doi:10.1364/OE.26.027021

1. Introduction

With the rapid development of the display technology and the improvement of people’s living standards, people’s requirements for display devices no longer solely focus on image quality and energy conservation [1–8]. Photobiological safety has become the focus of current display technologies. Photobiological safety mainly includes blue light hazard and circadian rhythm. Blue light hazard refers to the harm to the retina of human eye caused by the photochemical effect of blue light in the range of wavelength 400-500 nm [9,10]; while the circadian rhythm, also called the non-visual effect, refers to that the blue light component in the visible light, through inhibiting pineal gland to secret melatonin and stimulating the adrenal glands to secrete cortisol, changes the body’s circadian rhythm and adjusts their alertness and biological clocks [11].

In 1966, Noell W K et al. first reported that blue light can cause damage to rod cells [12]. In 2001, Dawson et al. conducted laboratory experiments with blue LEDs on rhesus monkeys and confirmed that blue light can damage the retina of the primate [13–15].In 2006, Peep V. Algvere et al. reported that Age-related maculopathy and the impact of blue light hazard [16]. In 2011, P. N. Youssef et al. introduced a blue light hazard mechanism [17]. In 2002, Berson et al. discovered intrinsically photosensitive retinal ganglion cells (ipRGC) which were visually unrelated to the retina. These cells were connected to the nerves of the suprachiasmatic nucleus (SCN) and the pineal gland and were able to regulate the body’s biological clock, which was the circadian rhythm [18]. Brainard et al. first measured the non-visual bio-spectral response curve - the circadian rhythm function, to demonstrate the intensity of influences of different wavelengths of light on the circadian rhythm of the human body [19–21]. At present, many international organizations have standardized and paid attention to the blue light hazard and circadian rhythm of lighting and display equipment. For example, CIE S 009/E:200, IDT and IEC/TR 62778 have provided the data of the weighting factor of blue light hazard and the calculation formula of the blue light hazard factor (CIE: International Commission on Illumination, IEC: International Electrotechnical Commission). CIE TN 003: 2015, ISO/TC274 N 201, and the American Medical Association in 2016 have all called attention to the circadian rhythm of artificial light sources (ISO/TC 274: International Organization for Standardization /Light and Lighting Technical Committee). Products with LED backlit-display are widely used in various equipment by people at all ages, such as game consoles for kids, office computers for adults, and e-readers for the elderly. Current devices with LED backlight displayer are usually able to adjust color temperature.

During 2015-2016, Rao Feng and Xu Ancheng et al. studied the changes of blue light hazard and circadian rhythm of LED backlight displayer and LED lighting with age [22]. However, in this paper, the transmittance of the lens was used as an approximation to replace the transmittance of the human eye, but the error was large. In addition, the physical significance of the relative blue light hazard factor and circadian rhythm factor was not clear. There are significant differences in the spectral distribution of LED backlight displayer at different color temperatures. We have not yet seen any correlation studies about the changes of blue light hazard or circadian rhythm with color temperature. The calculation of the blue light hazard factor and circadian rhythm factor is complex which requires the relevant response function expressions of human eye. It is necessary to find a simpler characterization method. Therefore, based on the data of human eye transmittance provided by CIE in 2012, this paper presented high-quality fitting of four response functions of human eye, and calculated the effective spectral distribution of LED backlight displayer at different color temperatures on the retinas of human eyes at different ages, and then calculated the effective spectral distribution of blue light hazard factor and circadian rhythm factor, and attempted to use the proportion of blue light in the range of wavelength 400-500 nm and the proportion of blue light in the range of wavelength 446-477 nm as approximations to characterize the blue light hazard and circadian rhythm. This conclusion can provide a certain theoretical reference for the personalized design and use of LED backlight displayer from the perspective of blue light hazard and circadian rhythm. Adherence to the specifications listed in this style guide is essential for efficient review and publication of submissions. Please note the references should appear at the end of the article after the Funding, Acknowledgments, and Disclosure sections.

2. Experiments

2.1 Principle

CIE/IEC 62471:2006 introduced the weighting factor of the blue light hazard in the visible light waveband. In 2001, Brainard GC et al. first measured the non-visual bio-spectral response curve, which was the circadian function. Subsequently, many people corrected the curve. This paper has adopted the data of Enezi J and Baczynska K. In 1924 and 1951, CIE introduced spectral luminous efficiency function of photopic and scotopic vision. The four response functions of human eye are represented by B(λ), C(λ), V(λ), and V'(λ), respectively, as shown in Fig. 1. According to Fig. 1, the peak wavelength of the blue light hazard is 437 nm. This wavelength corresponds to the maximum absorbance of A2E. When exposed to blue light, A2E would cause the shrinkage of retinal pigment epithelium and the death of photoreceptor cells. The circadian function is mainly located in the range of wavelength 446-477 nm, with the peak at 464 nm. The blue light within this wavelength can regulate the secretion of the melatonin in the pineal gland of the brain. The spectral luminous efficiency function of photopic vision V(λ) is determined by the cone-shaped cells on the retina which is capable of distinguishing colors, with the peak at 555 nm, corresponding to the brightness above 1 cd/m². The spectral luminous efficiency function of scotopic vision V’(λ) is determined by the rod-shaped cells on the retina which is capable of sensing light intensities, with the peak at 507 nm, corresponding to the brightness lower than 0.001 cd/m².

Fig. 1 Response functions of human eyes to visible light

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Referring to the lighting ratio S/P formula 1, IEC/TR 62778-2012 proposed to use the blue light hazard factor K_B to quantify the blue light hazard. See Eq. (2) for the formula. A number of papers proposed to use the circadian rhythm factor K_C to quantify the intensity of the circadian rhythm [2,11,22], see formula 3

\frac{S}{P} = \frac{1700 \int_{380}^{780} P (λ) V^{'} (λ) d λ}{683 \int_{380}^{780} P (λ) V (λ) d λ}

K_{B} = \frac{\int_{380}^{780} p (λ) B (λ) d λ}{K_{m} \int_{380}^{780} p (λ) v (λ) d λ}

K_{C} = \frac{K^{'}_{m} \int_{380}^{780} p (λ) c (λ) d λ}{K_{m} \int_{380}^{780} p (λ) v (λ) d λ}

In the formula, K_m, K_m’ represent the maximum spectral luminous efficacy of photopic vision and circadian rhythm respectively, and they are 683 lm/W and 3616 lm/W, respectively. V(λ), V’(λ), B(λ), C(λ), P(λ) represent the spectral luminous efficiency function of photopic vision, the spectral luminous efficiency function of scotopic vision, the weighting factor function of blue light hazard, the circadian rhythm function and spectral distribution function. The current data of the four response functions of human eye have large wavelength intervals. To accurately calculate the blue light hazard factor K_B and the circadian rhythm factor K_C, high-quality fitting of the response function is required.

According to CIE and other authoritative data, with the use of the Nonliner Curve Fit module of OriginPro software, the Asym2Sig function was adopted to fit the spectral luminous efficiency function of photopic vision V(λ), the spectral luminous efficiency function of scotopic vision V’(λ) and the circadian rhythm function C(λ). The function expressions of the fitting result are:

V (λ) = 3.659 \times 10^{- 4} + \frac{1.182}{1 + \exp (32.651 - λ / 15.731)} \cdot [1 - \frac{1}{1 + \exp (24.558 - λ / 20.915)}]

V^{'} (λ) = 4.9 \times 10^{- 3} + \frac{1.182}{1 + \exp (23.312 - λ / 19.803)} \cdot [1 - \frac{1}{1 + \exp (28.712 - λ / 16.081)}]

C (λ) = - 0.014 + \frac{1.741}{1 + \exp (14.397 - λ / 30.582)} \cdot [1 - \frac{1}{1 + \exp (24.824 - λ / 17.736)}]

For the weighting factor of the blue light hazard B(λ), with the use of the Fit Multi-peaks module of OriginPro software, multi-peak fitting was performed by superimposing five Gauss functions. The function expression of the fitting result is:

\begin{array}{l} B (λ) = 6.737 \times 10^{- 4} + 0.2361 \cdot \exp [- \frac{{(λ - 416.136)}^{2}}{20.276}] + 0.4443 \cdot \exp [- \frac{{(λ - 423.378)}^{2}}{215.925}] + 0.8606 \cdot \\ \exp [- \frac{{(λ - 447.663)}^{2}}{804.406}] + 0.1505 \cdot \exp [- \frac{{(λ - 480.662)}^{2}}{118.811}] + 0.0908 \cdot \exp [- \frac{{(λ - 471.588)}^{2}}{2697.525}] \end{array}

The fitting square of the correlation coefficient (R²) of the four response functions of human eye is shown in Table 1. The high fitting quality can guarantee the calculation accuracy in the following context.

Table 1. Fitting results of human eyes response functions

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From the B(λ) function in Fig. 1: $\int_{400}^{500} B (λ) d λ / \int_{380}^{780} B (λ) d λ = 0.956$ , it can be seen that 95.6% of the weighting factor function of the blue light hazard lies in the range of wavelength 400-500 nm, and the half-peak bandwidth of B(λ) is 71 nm, close to 100 nm. B(λ) can be approximated as 1 in the range of wavelength 400-500 nm and as 0 in other range. Therefore, this paper attempted to use the proportion of blue light RB in the range of wavelength 400-500 nm to quantify the hazard intensity of the blue light. Its geometric meaning is: the area ratio of the area of wavelength 400-500 nm and the wavelength 380-780 nm in the spectral distribution, the calculation formula is:

R_{B} = \frac{\int_{400}^{500} P (λ) d (λ)}{\int_{380}^{780} P (λ) d (λ)}

The circadian rhythm function is mainly located in the range of wavelength 446-477nm of the blue light [20,21,23,24]. This paper, by referring to the R_B calculation formula, attempted to approximately quantify the intensity of circadian rhythm by using the proportion of blue light RC in the range of wavelength 446-477 nm. The calculation formula is:

R_{C} = \frac{\int_{446}^{477} P (λ) d (λ)}{\int_{380}^{780} P (λ) d (λ)}

The proportion of blue light can be calculated without using the response function expression of human eye. According to the data of spectral distribution and the geometric significance of the proportion of blue light, it can be easily worked out using the software’s Integrate function, which can simplify the quantitative analysis of blue light hazard and circadian rhythm.

It is known from the mechanism of blue light hazard and circadian rhythm that the light must pass through the cornea, lens and vitreous body of the human eye and then shine to the retina to cause corresponding photobiological hazards. As people get older, the transmittance of their eyes decrease constantly. The spectral distribution on the retina of the same light source is different for people at different ages. The analysis and calculation of blue light hazard and circadian rhythm at present are directly performed based on the spectral distribution P(λ) measured by the spectrometer, without considering the influence of age. CIE 203-2012A introduced the calculation formula for the change of the transmittance of human eye with age [25]:

\begin{array}{l} D_{τ} (λ) = 0.06 + (0.15 + 3.1 \times 10^{- 5} a^{2}) {(400 / λ)}^{4} + 151.5492 \exp {- {[0.057 (λ - 273)]}^{2}} + \\ 2.13 \times (1.05 - 6.3 \times 10^{- 5} a^{2}) \exp {- {[0.029 (λ - 370)]}^{2}} + 11 .95 \times (0.059 + {1.8610}^{-}^{4} a^{2}) \times \\ \exp {- {[0.021 (λ - 325)]}^{2}} + 1.43 \times (0.016 + 1.32 \times 10^{-}^{4} a^{2}) \exp {- {[0.008 (λ - 325)]}^{2}} \end{array}

τ (λ) = 10^{- D_{τ} (λ)}

λ in the formula represents wavelength, the unit of which is nm, a represents age, the unit of which is year; D_τ(λ) represents the luminous density; τ represents transmittance, the unit of which is %. Equations (10) and (11) are used to calculate the transmittance of the human eye in the wavelength of 380-780 nm for people aging from 1 to 100 years old. The results are shown in Fig. 2.

Fig. 2 The spectral transmittances of different ages human eye

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From Fig. 2, it can be seen that in the visible light band, the transmittance of human eye in all ages increases with the increase of the wavelength. For blue-violet light with relatively shorter wavelength and higher photon energy, the transmittance of human eye in all ages is low. From the perspective of blue light hazard and circadian rhythm, this is a kind of self-protection that humans have long evolved for adapting to the environment. Ignoring the influence of the changes in pupil size and scattering of the human eye on the spectral distribution, the spectral distribution of the light source P(λ) measured by the spectrometer multiplies by the human eye transmittance τ(a) can obtain an effective spectral distribution P’(λ), which can irradiate to the retina. In this paper, according to the effective spectral distribution P’(λ) irradiated by the LED backlight displayer at different color temperatures on the retina of human eyes at different ages, the blue light hazard factor K_B, circadian rhythm factor K_C, the proportion of blue light in the range of wavelength 400-500 nm R_B and the proportion of blue light in the range of wavelength 446-477 nm R_C are calculated by Eqs. (2), 3, 8 and 9 respectively. A quantitative study on the correlation of changes of the blue light hazard and circadian rhythm of LED backlight displayer with different color temperature and age was performed.

2.2 Spectral measurement

The object of this study is a world-renowned mobile phone with an LED backlight LCD display, with a screen size of 5.5 inches (1 inch = 2.54 cm) and a pixel size of 1920 pixels × 1080 pixels. The color temperature of the screen was adjusted by the color temperature adjustment software of the mobile phone, and the USB2000 + spectrometer manufactured by Ocean Optics was used to measure the spectral distribution with the color temperatures of 1200K, 1900K, 2300K, 2700K, 3400K, 4100K, 5000K and 6500K respectively. The spectra were normalized with results shown in Fig. 3. The standard light source defined in ISO 3664:2000 is D50, and the color temperature is 5000K. Therefore, this article used 5000K as the daylight color temperature of the LED backlight displayer, and the total irradiance of wavelength band of 380-780 nm is 0.140 W/m².

Fig. 3 Normalized spectral of LED backlight displayer under different color temperature

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3. Results and Discussions

Based on the data of spectral distribution in Fig. 3 and the fitting results of the four response functions of human eye, the light ratio S/P, the blue light hazard factor K_B, the circadian rhythm factor K_c, the proportion of blue light in the range of wavelength 400-500 nm R_B and the proportion of blue light in the range of wavelength 446-477 nm R_c of LED backlight displayer at different color temperatures were calculated according to Eqs. (1, 2, 3, 8) and (9) respectively, with results shown in Table 2.

Table 2. The calculation results of parameters of LED backlight displayer under different color temperature

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As shown in Table 2, all of the five parameters increased with the increase of color temperature. When the color temperature increased from 1200K to 6500K, S/P, K_B, K_c, R_B and R_c increased by 5.03, 11.677, 10.064, 13.151 and 20.540 times respectively. It can be seen that the blue light hazard and circadian rhythm of LED backlight displayer increase rapidly with the increase of color temperature. According to the lighting ratio S/P, when the color temperature is lower than 1900K, the spectral luminous efficiency of photopic vision is greater than that of the scotopic vision. The color temperature of the LED backlight displayer is usually above 5000K when it is normally displayed, and at this time the spectral luminous efficiency of scotopic vision is greater than that of the photopic vision, the blue light hazard factor K_B of the LED backlight displayer, circadian rhythm factor K_c, the proportion of blue light in the range of wavelength 400-500 nm R_B and the proportion of blue light in the range of wavelength 446-477 nm R_c are all greater. Therefore, people should reduce the time spent on related equipment as much as possible.

3.1 Calculation of the effective spectral distribution on retina

According to the spectral distribution of different color temperatures P(λ) and the transmittance of human eye at different ages τ(λ), the effective spectral distribution on the retina of people at different ages by different LED backlight displayer P’(λ) was calculated with the formula P(λ) × τ(λ). Figure 4 shows the effective spectral distribution of the LED backlight displayer with a color temperature of 1200-6500K on the retina of humans aging from 1 to100 years old.

Fig. 4 Significant spectral on the retina of different ages of LED backlight displayer under different color temperature

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As shown in Fig. 4, for the same color temperature, since the transmittance of human eye decreases as the age increases, the effective spectral intensity on the retina sequentially decreases. Especially at high color temperatures, the intensity of the blue light in the range of wavelength 400-500 nm decreases significantly with age. For different color temperatures, the different spectral distribution of the LED backlight displayer lead to the huge difference of the effective spectral distribution on the retina. Therefore it is necessary to conduct a further correlation study on the changes of the blue light hazard and circadian rhythm of LED backlight displayer with age and color temperature.

3.2 Blue light hazard changes with color temperature

Based on the result of P’(λ) and the fitting results of the human eye response function in Fig. 4, the blue light hazard factor K_B and the proportion of blue light in the range of wavelength 400-500 nm R_B corresponding to different color temperatures and ages were calculated according to Eqs. (3) and (5). The change curve of K_B and R_B at different color temperatures for people aging from 1 to 100 years old were drawn, see Fig. 5.

Fig. 5 Blue light hazard of LED backlight displayer change with color temperature for different ages (a: blue light hazard factor change with color temperature; b: 400-500nm blue light ratio change with color temperature)

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Comparing the two figures, it can be seen that except for the value of the ordinate, the growth rates and spacing of the curves in the two figures are almost identical. The blue light hazard at various ages increase with the increase of color temperature, and the younger the people are, the faster the growth rate is. Taking a one-year-old infant as an example, when the color temperature increased from 1200K to 6500K, the blue light hazard factor increased from 6.657 × 10⁻⁵ W/lm to 8.141 × 10⁻⁴ W/lm, 12.2 times higher; the proportion of blue light in the range of wavelength 400-500 nm increased from 1.8% to 29.3%, 16.3 times higher. From the above analysis, we can see that LED backlight displayer are harmful to young people, especially to those under the age of 40. They should reduce the time spent on related equipment and pay attention to the blue light hazard.

3.3 Blue light hazard changes with age

According to the above calculation results, the change curve of the blue light hazard factor K_B and the proportion of blue light in the range of wavelength 400-500 nm R_B at color temperatures within 1200-6500K for people at different ages were drawn, see Fig. 6.

Fig. 6 Blue light hazard of LED backlight displayer change with ages for different color temperature (a:blue light hazard factor change with ages;b:400-500nm blue light ratio change with ages)

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The comparison showed that the changes in the two figures almost coincided at each color temperature. So we can get that the proportion of blue light in the range of wavelength 400-500nm can be used as an approximation to replace the blue light hazard factor to characterize the intensity of blue light hazard, which can get the result: R_B≈369.0K_B. As shown in Fig. 6, the color temperature of the LED backlight displayer is in the range of 1200K to 6500K. For humans aging from 1 to 100 years, the blue light hazard factor K_B and the proportion of blue light in the range of wavelength 400-500 nm R_B both decrease when people grow older. And as the color temperature increases, the rate of decrease grows rapidly. For people older than 40, K_B and R_B decrease significantly. Taking the color temperature 6500K as an example, when the age increased from 1 year to 100 years old, the blue light hazard factor decreased from 8.141 × 10⁻⁴ W/lm to 1.773 × 10⁻⁴ W/lm, 0.2 times lower; the proportion of blue light in the range of wavelength 400-500 nm decreased from 29.3% to 8.0%, 0.3 times lower. When the color temperature is lower than 2300K, K_B and R_B for people aging from 1 to 100 years old are relatively small, and have little change with age. From the above analysis, we can see that LED backlight displayer are harmful to young people, especially to those under the age of 40. They should reduce the time spent on related equipment and pay attention to the blue light hazard.

3.4 The circadian rhythm changes with color temperature

Based on the result of P’(λ) and the fitting results of the response function of human eye in Fig. 4, Eqs. (4) and (6) were used to calculate the circadian rhythm factor K_c, the proportion of blue light in the range of wavelength 446-477 nm R_c corresponding to the effective spectral distribution of LED backlight displayer at different color temperatures on the retinas of human eyes at different ages. The change curve of K_c and R_c for people aging from 1 to 100 years old were drawn, see Fig. 7. It can be seen from the two figures that, when the color temperature is higher than 2300K, the growth rate and spacing of each curve in the two figures are similar; when the color temperature is lower than 2300K, there is a large difference.

Fig. 7 Circadian effect of LED backlight displayer change with color temperature for different ages (a:Circadian factor change with color temperature; b:446-477 nm blue light ratio change with color temperature)

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As shown in Fig. 7, for people aging from 1 to 100 years old, K_c and R_c both increase with the increase of the color temperature within the range of 1200-6500K. Taking a 1-year-old infant as an example, when the color temperature increases from 1200K to 6500K, K_c increased from 0.4 to 3.8, an increase of 9.5 times; R_c increased from 0.9% to 19.6%, an increase of 21.8 times. When the color temperature is in the range of 1900K-3400K, the growth rates of K_c and R_c are the fastest for people at all ages. According to the above analysis, for users of LED backlight displayer at various ages, the color temperature of screens should be lowered as much as possible from the perspective of reliving the circadian rhythm effect.

3.5 Circadian rhythm changes with age

According to above calculation results, the change curve of the circadian rhythm factor K_c, the proportion of blue light in the range of wavelength 446-477 nm R_c with age were drawn, see Fig. 8. It can be seen from the comparison that the distances between 1200K and 1900K in the two figures are quite different. Therefore, under low color temperatures, R_c cannot be used as an approximation to replace the circadian rhythm factor K_c to characterize the intensity of the circadian rhythm.

Fig. 8 Circadian effect of LED backlight displayer change with ages for different color temperature (a:Circadian factor change with ages; b:446-477 nm blue light ratio change with ages)

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As shown in Fig. 8, the color temperature of the LED backlight displayer is in the range of 1200K to 6500K. For people aging from 1 to 100 years old, the circadian rhythm factor K_c and the proportion of blue light in the range of wavelength 446-477 nm R_c decrease with aging. And as the color temperature increases, the rate of decrease grows. When people are older than 40 years old, the decrease speed of K_c and R_c are faster. Taking the color temperature 6500K as an example, when the age increased from 1 year to 100 years old, the circadian rhythm factor K_c decreased from 3.8 to 1.2, 0.3 times lower; R_c decreased from 19.6% to 5.1%, 0.26 times lower. When the color temperature is lower than 2300K, the value of K_c and R_c are relatively small for people aging from 1 to 100 years old, and have little change with age. From above analysis, it can be concluded that LED backlight displayer have a greater influence on young people’s circadian rhythm, especially on those under the age of 40. They should reduce the time spent on these equipment and pay attention to the circadian rhythm.

4. Conclusion

According to the fitting results of the four response functions of human eye, the transmittance of human eye of people aging from 1 to 100 years old and the spectral distribution of LED backlight displayer in the range of wavelength 1200-6500K, the blue light hazard factor KB, the circadian rhythm factor Kc, the proportion of blue light in the range of wavelength 400-500 nm RB and the proportion of blue light in the range of wavelength 446-477 nm Rc were calculated corresponding to the effective spectral distribution of LED backlight displayer at different color temperatures on the retinas of human eyes at different ages. A study on the correlation of changes of the blue light hazard and circadian rhythm of LED backlight displayer under different color temperatures and ages was performed and the following conclusions were obtained.

(1) For LED backlight displayer users aging from 1 to 100 years old, the blue light hazard and circadian rhythm intensify as the color temperature increases in the range of wavelength 1200K to 6500K. Taking one-year old infants as examples, when the color temperature increased from 1200K to 6500K, the blue light hazard factor and circadian rhythm factor of the effective spectrum of the retina increased by 12.2 and 9.5 times, respectively.
(2) For LED backlight displayer with the color temperature in the range of wavelength 1200-6500K, the blue light hazard and circadian rhythm decrease as age grows among users aging from 1 to 100 years old. Taking a LED backlight displayer with the color temperature of 6500K as an example, when the age increased from 1 year to 100 years old, the corresponding value of the two factors decreased by 0.2 and 0.3 times respectively.
(3) LED backlight displayer have a greater influence on young people’s circadian rhythm, especially on users under the age of 40. They should reduce the time spent on these equipment and pay attention to the circadian rhythm.
(4) The proportion of blue light in the range of wavelength 400-500 nm can be used as an approximation to replace the blue light hazard factor to characterize the intensity of the blue light hazard, which can get the result: R_B≈369.0K_B.

This conclusion can provide a certain theoretical reference for the personalized design and use of LED backlight displayer from the perspective of blue light hazard and circadian rhythm.

Funding

National Key Research and Development Program of China “Strategic Advanced Electronic Materials” (2017YFB0403704); Natural Science Basic Research Plan in Shaanxi Province of China (Program No. 2017JQ6011).

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T_c / K	S/P	K_B / W/lm	K_c	R_B / %	R_c / %
1 200	0.447	8.374 × 10⁻⁵	0.437	2.595	1.055
1 900	0.918	8.923 × 10⁻⁵	0.731	3.621	1.366
2 300	1.12	1.619 × 10⁻⁴	1.087	6.350	3.186
2 700	1.30	2.582 × 10⁻⁴	1.500	10.225	5.625
3 400	1.57	4.326 × 10⁻⁴	2.226	16.744	10.032
4 100	1.78	5.805 × 10⁻⁴	2.826	22.161	13.553
5 000	2.00	7.641 × 10⁻⁴	3.552	27.747	17.409
6 500	2.25	9.778 × 10⁻⁴	4.398	34.126	21.670

T_c / K	S/P	K_B / W/lm	K_c	R_B / %	R_c / %
1 200	0.447	8.374 × 10⁻⁵	0.437	2.595	1.055
1 900	0.918	8.923 × 10⁻⁵	0.731	3.621	1.366
2 300	1.12	1.619 × 10⁻⁴	1.087	6.350	3.186
2 700	1.30	2.582 × 10⁻⁴	1.500	10.225	5.625
3 400	1.57	4.326 × 10⁻⁴	2.226	16.744	10.032
4 100	1.78	5.805 × 10⁻⁴	2.826	22.161	13.553
5 000	2.00	7.641 × 10⁻⁴	3.552	27.747	17.409
6 500	2.25	9.778 × 10⁻⁴	4.398	34.126	21.670

Change of blue light hazard and circadian effect of LED backlight displayer with color temperature and age

Abstract

1. Introduction

2. Experiments

2.1 Principle

2.2 Spectral measurement

3. Results and Discussions

3.1 Calculation of the effective spectral distribution on retina

3.2 Blue light hazard changes with color temperature

3.3 Blue light hazard changes with age

3.4 The circadian rhythm changes with color temperature

3.5 Circadian rhythm changes with age

4. Conclusion

Funding

References

Cited By

Figures (8)

Tables (2)

Equations (11)

Optics Express