OLEDs are organic LEDs, which means that their key building blocks are organic (i.e. carbon-based) materials. Unlike LEDs, which are small point sources, OLEDs are made in sheets and are diffuse area light sources. OLED technology is evolving rapidly, and the efficacy, longevity, and color quality specifications of some products have surpassed those of their conventional lighting and LED counterparts.

The OLED spectrum is different from any other lighting spectral curve that humans have ever experienced, with peaks in the blue, green, and red bands. The reason for this is that under normal lighting conditions, the ability to finely delineate information in the visual field is primarily dependent on the photoreceptors of the S, M, and L cone cells. Due to the information processing mechanism of the optic nerve, the optimal output can only be obtained by configuring the spectrum in accordance with the ratio of these 3 types of cells. Avoid visual fatigue and improve efficiency.

The OLED spectrum has the following characteristics:

No ultraviolet and violet light

Ultraviolet and visible light in the ultraviolet light is extremely high in energy and has a destructive effect on organic macromolecules. Nowadays, ultraviolet light is the conventional way of sterilization, and human skin cancer is also mainly due to excessive ultraviolet rays in sunlight. The current natural conditions of ultraviolet light is still strong enough to be harmful to the human body, if not well protected, ultraviolet light from the outside of the eye into the interior, on the cornea, pupil, lens, retina and so on will have the size of the damage. According to some data, about 13 million people worldwide suffer from cataracts every year, 20% of which are caused by UV rays, which is why there are UV indices and sunscreen recommendations in weather forecasts.

Traditional fluorescent lamps and violet LED lamps are both UV-excited, with an excess of UV and violet light in the visible light, posing a health risk for long-term use. The OLED spectrum is completely free of UV light, and the measured data supports this view.

No harmful blue light

Harmful blue light damages the eye structure: Harmful blue light has extremely high energy, which can penetrate the lens and reach the retina, causing the retinal pigment epithelial cells to shrink or even die. The death of the photosensitive cells will lead to vision loss or even complete loss of vision, and this damage is irreversible. Blue light also causes macular degeneration. The lens of the human eye absorbs some of the blue light and gradually becomes cloudy, resulting in cataracts. Most of the blue light penetrates the lens, especially in children, where the lens is clearer and less able to withstand the blue light, making it more likely to cause macular degeneration and cataracts.

Harmful blue light causes visual fatigue: Due to the short wavelength of blue light, the focal point does not fall in the center of the retina, but a little further forward from the retina. In order to see clearly, the eyeballs will be strained for a long time, causing visual fatigue. Prolonged visual fatigue may lead to myopia deepening, double vision, easy to read serial, attention can not focus and other symptoms, affecting people’s learning and work efficiency.

Harmful blue light inhibits the secretion of optic melanin and affects sleep. This also explains why playing cell phones or tablets before bedtime can cause poor sleep quality or even difficulty in falling asleep.

For 435nm blue light, there is a visual health risk as long as the luminance value is greater than 1150cd/m2, which is less than half the brightness of the moon (at full moon). OLED light sources do not have this problem. See Table 1.

Table 1 Risk – free measured values of OLED spectrum

Blue light of suitable wavelength

The starting point of blue light for OLED lighting is around 450 nm, which avoids harmful blue light. It should be noted that blue light is an important component of white light. Without it, the color of an object cannot be truly reflected. Therefore, the claim that some desk lamps on the market advertise blue light filtration is one-sided. Moreover, blue light by stimulating the adrenal glands to secrete corticosteroids, etc., play a role in changing physiological rhythms, regulating the human biological clock, also known as non-visual biological effects.

This is the result of natural selection, mammals and reptiles common ancestors have four-color vision. However, mammals were at a disadvantage in the competition at that time, and were forced to live day and night or in the dark, and the four-color vision gradually degenerated into three-color vision, or even two-color vision. What was retained during this period was the ability to perceive blue and green, thus showing that the color blue is essential.

Through precise design, the proportion of blue light in the OLED spectrum is similar to the proportion of cone cells in the retina that perceive blue light.

Green light is the most predominant

Figure 2 shows that human sensitivity to color (wavelength) is different under different brightness environments. It can be seen that the human eye is most sensitive to green light (wavelength 507 ～ 555 nm). The reason for this is twofold: first, among the cone cells, M-type cone cells, which can receive green spectrum, account for the largest proportion and have a large number of receptors; second, due to the transmission mechanism of visual signals in the nervous system, both L-OFF and M-On type optic nerve cells can efficiently transmit signals of green spectrum. Secondly, due to the transmission mechanism of visual signals in the nervous system, both L-OFF and M-On type optic nerve cells can efficiently transmit signals of green spectrum.

Fig. 2 Color sensitivity at different brightness levels

Low yellow-orange light

First of all, it should be noted that the yellow-orange spectrum is not identical to the yellow-orange color, as the former cannot be split by prisms, while the latter can be split into red and green colors. The yellow-orange spectrum has the largest number of “receptors,” and both the M and L types of cone cells, which perceive the green and red spectrums, can perceive yellow-orange light very well – activated by yellow-orange light. This is shown in Fig. 2.

Fig. 2 Visual sensitivity of cone cells atdifferent wavelengths

However, the visual signaling mechanism that has evolved over time is not conducive to signaling in the yellow-orange spectrum: as mentioned earlier, efficient output can only be obtained when the center-edge input signal is reversed, i.e., center-edge withdrawal or center-limit withdrawal, in the connecting region of the nerve cell. Among the six ganglion cells, only S – OFF (when M + L is ON) can efficiently output signals in the yellow-orange spectrum (when S is off and M + L is on); S – ON can be ignored at this time. – M – ON, M -OFF, L – ON, L – OFF Both the center and the edge of the sensing area of the nerve cells are in the state of excitation (both M and L can sense light and output), forming a blockage, and the output can be gradually restored only by lateral adjustment, such as by the horizontal cells.

Fig. 2 Diagram of ganglion cells regulating sensory output

In this process, most of the receptors that consume amazingly are open–except for the blue light-sensitive S-type cone cells (the smallest proportion), the green cone and red cone cells are all open. However, most of the output channels are blocked or inefficient – light is perceived, but the information is not transmitted, resulting in half the effort. We can also feel in life, dim light easy to cause fatigue and sleepiness. It should be added that OLED reduces the yellow-orange spectrum, the intuitive brightness feeling is “not bright”. Humans mainly rely on red, green and blue 3 kinds of cone cells to form vision, no yellow spectrum does not affect the visual experience, and lower luminous flux on the eye to reduce eye stimulation, reduce eye cell loss, while avoiding channel blockage.

High red light

As mentioned earlier, due to the reptile suppression to the predominantly nocturnal, mammals for a long time degraded to only two-color vision, until now felines are still color blind. However, after the emergence of primates, three-color vision was gradually restored, and the increase was the ability to recognize red. In nature, the color red often represents ripe fruit, and being able to spot the fruit before competitors facilitates survival and reproduction. Also blood and muscles are red, meaning high protein and energy. Over time, cultures have coincidentally considered the color red to be a symbol of life.

Objectively speaking, due to the longer wavelength of red light, the corresponding receptors are more depleted. But whether because of the good feeling for red light left in human genes or the reality of positive feedback from the body’s response to red light stimuli, evolution ultimately chose to recognize the red light spectrum as a direction to increase the number of optic cones. L The percentage of cones is also illustrative – under natural conditions, useless organs are abandoned rather than strengthened.

Conclusion

To summarize, starting from the operation law of human visual system, we can conclude that OLED spectral characteristics are in line with the operation law of human visual system through research.

In the long run, the future market will have a very good development. Of course, it should be pointed out that the reduction of yellow-orange light avoids the repeated activation of red- and green-sensitive cone cells, which in turn keeps the ganglion cells in a highly efficient state.