LED light blue | expert interpretation

Light enters the human eye with two visual channels, one for the imaging visual channel (solid line in Figure 1) and the other for the non-imaged channel of the circadian clock and hour (the dotted line in Figure 1). On the imaging vision channel, the blue light of the LED luminaire may create a visual hazard to the retina. On non-imaging channels, the blue light of an LED luminaire may have an effect on the circadian rhythm.

Figure 1 Imaging vision channel and non-imaging vision channel for human eyes receiving light

The wavelength of the blue LED is around 450 nm, which is exactly the same as the human body's circadian rhythm/biological clock rhythm. It has a strong ability to secrete melatonin inhibitors. The reduction in melatonin makes people excited and does not sleep. Longer this will affect people's immune mechanisms.

Figure 2 is a typical 5500K blue-rich LED white light emission spectrum, with a thick line depicting the maximum spectral energy wavelength in the 460nm region, which coincides with the human body's spectral curve for the secretion of melatonin inhibitors. As a result, long-term companionship will affect The circadian rhythm of the human body's normal sunrise and sunset, so it is very important to limit the blue light energy below 500nm and reduce the influence on human circadian rhythm.

In order to avoid the possible adverse effects on the human health caused by the use of rich blue LED lamps, the color temperature of indoor LED lamps should not exceed 4000K.

The influence of blue light on the circadian rhythm of LED lamps is usually included in the performance indicators of the product standard.

Fig.2 Spectral sensitivity curve of blue LED white light spectrum curve and melatonin inhibitor

The coincidence indicates that the blue LED white light at night is unfavorable.

How is the blue light of LED lamps formed?

In order to obtain stable, reliable and simple white light, the most common method currently used is to excite yellow phosphors with blue-emitting LED chips. The LED emits blue light with a wavelength of about 450 nm. The blue light is divided into two parts in this process. A part of the blue light excitation phosphor emits yellow-green light with a wavelength of about 570 nm, and the other part of the blue light is transmitted and mixed with the yellow-green light generated by the excitation phosphor to produce white light. As shown in Figure 3.

Figure 3 blue LED chip plus phosphor to produce white light

Color temperature is the most common indicator of the spectral quality of the source. According to the proportion and composition of the phosphor, the white LED can provide a full range of color temperature range of cool white, neutral and warm white with a color temperature between 2700 and 6500K.

When the color of the light emitted by the light source is the same as the color of the black body (which is a complete radiator, black) radiated at a certain temperature, the temperature of the black body is called the color temperature of the light source. In blackbody radiation, the color of the emitted light varies with temperature, and the black body exhibits a gradual process of red-orange-yellow-yellow-white-white-blue-white, that is, the process of color temperature from low to high. The higher the temperature of the "black body", the more blue components in the spectrum and the less red components. For example, the color of an incandescent lamp is warm white, its color temperature is 2700K, and the color temperature of a daylight fluorescent lamp is 6000K.

The change of sunlight during the daytime in nature represents the change in color temperature of the illuminant. Morning and evening sun light 2000 ~ 3000K (warm white light); morning 8:00 sun light 4000K (cold white light); noon around the sun light 5000 ~ 6000K (daylight color).

The warm temperature of "warm light" is lower, while the color temperature of "cold light" is relatively high. After the color temperature is increased, the proportion of blue light radiation increases, and the content of blue light increases. At the same time, brightness also affects the proportion of blue light.

Generally, a color temperature of 2700 to 4000 K is referred to as a low color temperature. The color temperature of 5000 to 6500 K is called high color temperature. White light with a high color temperature is also called "rich blue" white light due to its high blue light content.

What is the blue light hazard of LED lamps?

Since the LED light source has the characteristics of small light-emitting area and high brightness, and blue light has shorter wavelengths than other light colors, it has greater radiant energy, and the possible radiation hazard is larger than that of other colors. The blue light hazard refers to the hazard caused by the 400-500 nm blue light band in the light source. If the brightness of an LED lamp is too high, the eye may cause photochemical damage of the retina after long-term direct view of the illuminant. The degree of blue light hazard depends on the amount of blue light that the human eye accumulates under the light.

According to the longest exposure time for each injury not exceeding the exposure limit, the hazard level is divided into four levels as shown in the following table:

There are currently several regulations as follows:

(1) The luminaire does not use an LED light source with a blue light hazard greater than RG2.

(2) The indoor LED lamp blue light hazard is not greater than RG1.

(3) Night lights installed on portable luminaires and power outlets for children shall not exceed RG1.

(4) RG0 (non-hazardous) LED lamps are recommended for special populations (such as those affected by diabetes and photosensitizing drugs) or for special positions (such as infants) that may be directly looking at LED lamps.

It can be seen that considering the damage caused by the human eye to the human eye in a short time or moment, the blue light hazard is considered when the blue light radiance reaches the standard RG2 or above.

The assessment of blue light hazards is usually included in the safety indicators of the product standard.