It's okay for the elderly to pay attention to their health, but they must keep their eyes open to avoid being cheated.
The following is the introduction of laser, which cannot directly irradiate the skin:
Even the 1 laser is considered to be potentially dangerous. The first laser created by Theodore Mayman was only as powerful as "Gillette" and could only burn the blades of Gillette razors. However, a few milliwatts of low-power irradiation is enough to harm people's vision. If the wavelength of the laser is within the range where the cornea and lens can focus on the retina well, it means that this divergent laser with low coherence will be focused on a very small area of the retina by the eyes, which will cause local burns and permanent damage to the retina in just a few seconds or less.
Lasers are usually marked with laser warning labels with safety grade numbers:
Class 1 (Class I/ 1): It is safe in the equipment. Usually because the light beam is completely closed, such as in a CD player.
Grade 2 (Class II/2): It is safe under normal use conditions, and the blink reflex of eyes can avoid injury. This kind of equipment usually has a power of less than 1mW, such as a laser pointer.
Class IIIa/3R: The power usually reaches 5mW, and there is little risk of eye injury in blink reflex time. Watching this light beam for a few seconds will cause immediate damage to the retina.
Grade 3b/B (grade IIIb /3B): When exposed, it will cause direct damage to eyes.
Grade 4 (IV/4): Laser will burn the skin, and in some cases, even scattered laser will cause harm to eyes and skin. Many industrial and scientific lasers fall into this category.
This marked power is for visible light and continuous wavelength lasers, and there are other applicable restrictions for pulse lasers and invisible light lasers. For those who use class 3B and class 4 lasers, goggles that can absorb light with a specific wavelength are also needed to protect their eyes.
Some infrared lasers with wavelengths exceeding 1.4μM are usually classified as "human eye safety". This is because the inherent molecular vibration of water molecules strongly absorbs the frequency spectrum near this band, so the laser with these wavelengths will be diluted when passing through the cornea, and the residual light cannot be focused by the lens to reach the retina. But the label "eye safety" may be misleading, because it is only applicable to low-power continuous beams. Any high-power laser with Q-circuit breaker can also burn cornea at this wavelength, causing serious eye damage.