In-depth interpretation of Blu-ray hazards: Does Blu-ray really cause eye damage?

LED semiconductor lighting Reuters According to official statistics, China's 7-12 years old, 13-15 years old, 16-18-year-olds suffering from eye diseases probability of 45.71%, 74.36% and 83.28% respectively, the incidence rate of adolescent eye surpass Japan as the world The first big country.

People generally classify the reasons as two aspects. First, the children's homework is stressful, excessive use of the eyes, the incorrect sitting posture also accelerates the damage to the eyes; the second is the long-term opposition to electronic products such as mobile phones and tablet computers. Two factors have caused eye fatigue in adolescents, resulting in decreased eye regulation, which in turn induces eye diseases.

However, is this really the only thing?

Last year, a World Health Organization (WHO) Eye Association's research report went on the go. The report pointed out that "the potential hidden threat of blue light hazard to humans will far exceed the destructiveness of Sudan red, melamine, SARS, H1N1, invisible. In the eyes of people. Although, this so-called WHO research report has been confirmed as false news. But the term blue light hazard has entered the public's sight.

So, does the "blue light hazard" have any harm to the eyes and how much damage? We are here today to restore the truth to the facts.

First, let's explore the first question. Does Blu-ray really hurt the eyes?

The following is the answer to this question in the CIE S 009/E:2012 study published by the International Commission on Illumination CIE in 2002:

Figure 1 CIE S 009/E: 2012 Appendix A.3

The effect is that blue light can cause photochemical damage to the retina, mainly concentrated in the epidermal cells of the retinal pigment, and forms arcs and blind spots on the retina.

Figure 2 Human eye structure

What do you mean? The reason why the eye can see things is because there are rods and cones on the retina. There is a place in the axial end of the retina called the fovea. This is the area with the most acute vision and the most abundant visual cells. And it appears yellow because it is rich in lutein. Under normal circumstances, the aging of the macula with age increases visual decline. However, under the long-term exposure to blue light, excessive blue light directly enters the retina and generates a large amount of free radicals, which causes accelerated oxidation of the macula. Eventually, the visual cells in the macula are largely killed, and the damage cannot be repaired by itself.

The second question is, is there only blue light with blue light?

Look at the following three spectra. (From left to right, tungsten filament lamps (incandescent lamps), fluorescent lamps, LED lamps)

Figure 3 Spectral distribution of different light sources

The colors of these three sources are warm, white, and cool white. It can be seen that even the daily incandescent lamps emit warm light, which also contains blue light components. That is to say, blue light components are commonly found in various lamps and light sources. The only difference is that the blue color light does not contain other colors. ingredient. Moreover, it should be pointed out that the white LED emits yellow-red light by the blue light, and then combines its own blue light to form white light, so the proportion of the blue light component is more concentrated than other types of light sources.

The third question, is it better to replace all LED lights with fluorescent or tungsten lamps?

the answer is negative. Figure 4 is a grading diagram of the hazard of the source strobe to the observer in the "IEEE PAR 1789-2015 Risk Assessment Draft LED Lighting Flicker Potential Health Effects", with the green part being the undetectable area (no hazard area) and the yellow being low In the risk zone, white is a hazardous area.

Although the limit frequency that can be discerned by the human eye is about 60 Hz, that is, it is difficult to distinguish the 60 Hz, 100 Hz, and 3000 Hz illuminating frequencies by vision. But still the old saying, not seen is not necessarily harmless. A large number of studies have pointed out that long-term exposure to the smoldering environment of the harmful light source, such as eye fatigue, vision loss, and dizziness, nausea and nervous system damage.

Since incandescent lamps and fluorescent lamps are directly operated at the power frequency, the frequency of their illumination is about 100 Hz (see Figure 5 for waveforms), and the upper limit of the standard for the depth of fluctuation at this frequency is 3.3%. Fluorescent lamps that rely solely on thermally stable incandescent lamps or phosphors are difficult to meet this requirement.

LED has innate advantages in this respect. Due to its PWM control, the illuminating frequency can often reach 1500 Hz or even 3000 Hz or more, and at this frequency, no matter how large the fluctuation depth of light is, it is safe. In other words, the stroboscopic hazard is a big problem for traditional light sources, and for LED products , it is a problem that can be solved with ease.

Figure 4 IEEE PAR 1789-2015 stroboscopic hazard rating map

Figure 5 Traditional light source stroboscopic waveform

On the other hand, due to the easy dimming of LEDs and the integration of multiple chips in a single luminaire, better color reproduction and reduced visual fatigue can be achieved.

That is to say, LEDs have advantages over conventional light sources in terms of stroboscopic hazard control, color reproduction, etc., and are also more energy efficient, not to mention that any band of light components are harmful as long as they are excessive, so there is no need to waste food.

So, what is the last question today, what kind of LED products are harmless?

In the old saying, all the dangers of throwing away doses are hooligans.

So, where is this “dose” or “degree”?

Let's first take a look at the relevant literature and regulations at home and abroad.

First, the aforementioned CIE S 009 was later adopted by the International Electrotechnical Commission (IEC) IEC and became the light biosafety of the IEC 62471:2006 lamp and lamp system. This is the first international technical regulation on photobiosafety. This IEC 62471:2006 was adopted by the European Union and tightened some of the requirements and became EN 62471:2008, and was mandated in the EC/244/2009 EUP Directive. Later, the time was transferred to 2014, and the IEC 60598-1-2014 published this year included the IEC/TR 62778:2014 Blu-ray Hazard project and was enforced.

Domestically, it follows the IEC route. First, GB/T 20145-2006 was issued in China with reference to IEC 62471:2006. Secondly, GB 7000.1-2015 also added the requirements of IEC/TR 62778 with reference to IEC 60598-1-2014. In other words, this Blu-ray hazard has laws and regulations that can be relied upon at home and abroad.

Figure 6 Schematic diagram of the field of view of the light source

So let's take a look at how the technical regulations (standards) are specified. First, IEC/TR 62778:2014 follows the test principles and basic methods of IEC 62471:2006. The blue light hazard is divided into two categories: spectral irradiance and spectral radiance. Illuminance is the energy of a light source that is projected onto a unit area as a point source; brightness is just the opposite. It is the point of view of the human eye as a point to look directly at the light source. The following are the limits for the blue light hazard given in IEC 62471:2006.

Figure 7 IEC 62471:2006 Limit Requirements

It can be seen that the standard is divided into three levels, namely exemption level, low risk and medium risk. Among them, GB 7000.1-2015 stipulates that the blue light hazard of the luminaire products should not exceed the low risk, and the blue light hazard of the children's portable luminaires and the power outlet night light products cannot exceed the exemption level.

Then, when it comes time to knock on the blackboard, how can we judge the level of the blue light hazard of a lamp?

First of all, the most accurate way is to see if the product has passed the relevant certification (CCC, CQC, etc.), or to look at the unqualified record notification of the product.

Secondly, it is roughly inferred from the information on the product packaging and product design. The following figure shows the spectral distribution of different color temperature LED light sources of the same power. It can be seen that the blue color component (about 430 nm to 490 nm) of the LED with high color temperature (cold color) is far higher and better (lower color).

Figure 8 Spectrum distribution with color temperature changes

Here is a set of combined data for different color temperature and low photometric luminosity recommended by IEC. The following figures are the recommended data for brightness at different color temperatures and illumination at different color temperatures. It can be seen that the recommended luminosity of 2350K, 4000K and 6500K is not higher than 40Mcd/m2, 8.5 Mcd/m2, 5 Mcd/m2 brightness and 4000Lx, 850Lx, 500Lx illuminance. That is to say, the lower the color temperature, the greater the allowable luminosity.

Figure 9 IEC recommended low-risk blue light color temperature and brightness combination

Figure 10 IEC recommended low-risk blue light color temperature and illumination combination

Combined with the comprehensive factors of identification, color reproduction and energy efficiency, it is recommended to select lamps with color temperature between 3500K-5000K, desk illumination between 300Lx-1000Lx and indoor illumination between 100Lx-350Lx. The color temperature product outer packaging is generally marked, and the illuminance value can be roughly calculated by the installation height, the area to be used, and the total power of the product.
For example, if the illumination surface of the 13W LED table lamp is about 1000 Lx from the height of the desktop 400mm, then if you plan to buy a LED lamp with a similar height, the power should be between 7W-13W. The installation height is doubled and the illumination is attenuated by 4 times.

For example, if the living room area is 50 square meters and the height is about 3.5 meters, then the equivalent area of ​​the wall is about 100 square meters. To reach the illumination level of 100Lx, the luminous flux of 100m2×100 Lx=10000 lm is needed, then LEDs generally have an energy efficiency level of 100 lm/W, so you need to install a luminaire with a total power of about 100W.

Finally, choose a luminaire with a light diffuser (milk mat). Below is a set of comparison data, we can see that the same sample number white and black two sets of test data respectively represent the results with a frosted cover and remove the frosted cover. It can be seen that after removing the frosted cover, the brightness of the blue light is generally increased by between 10 and 100 times.

Figure 11 Comparison of blue light hazards before removing the frosted cover