As you move away from the bulb, you see a quarter of the light every time the distance is doubled. A laser gives light in one small beam. If it gets into the eye, you receive all the laser's energy, not just a fraction. Third, a light bulb gives off light at many different wavelengths different photon energies. A laser is a pure tone, only one wavelength. The coherent light will be more damaging. The common red laser pointer is a diode laser, really just a special type of transistor, or diode.
Because of the unique features of laser light, it is magnified by , times as it passes through the eye. The light passes to the back part of the eye, the retina, which is where we perceive vision. The eye actually sees a small part of the electromagnetic spectrum that runs from short cosmic ray energies to long radiowaves. We see only from violet to red. Infrared IR and ultraviolet UV are just outside our ability to see.
The eye is most sensitive to yellow-green light nm. At the same power, nm red light is only 3 percent as bright. When determining safety limits for the laser pointer or in other areas, a value must be chosen. Above a certain number is illegal or dangerous, below is OK. In real life many factors contribute to something becoming harmful.
Look at traffic laws. Seventy miles per hour may be legal while 71 earns you a ticket, yet it is not really more dangerous. But mph is much riskier, and 50 mph may be dangerous if the road is covered with ice. So with laser pointers, different conditions determine when retinal damage will actually occur.
In FDA-regulated pointers, the laser power limit is set at one-tenth the actual threshold of damage. Well, research shows that anything more than a quarter of a second will likely increase your chance of damage to your eye. And this research was undertaken with a laser that was only 1 mW, so it is assumed that if a laser is more powerful than this, then less time may expose our eye to more danger. Fortunately, your eyes have a natural reflex which makes them close within 0.
The most that you are likely to get in terms of damage from a lower class laser pointer is flash blindness. Flash blindness is essentially just where you get temporary blindness due to the high intensity of the light flashing in your eyes.
This is pretty common. Now, if you hold a laser to your eye for more than a few seconds — this can be a 1 mW or a 5 mW laser — then it does have the opportunity to damage your retina. Whether or not this will be temporary or permanent is unknown — the majority of times retina damage is temporary, but there are cases of where retina damage has been permanent.
These lasers have the ability to permanently blind you. If you use laser pointers that are in excess of 5 mW and anywhere into level 4 categories, then you need to be completely safe with this type of laser. The short answer to this is yes, they are.
This is quite simply because your retina will more easily absorb a green laser than it will a red laser. This makes your retina far more vulnerable to a green laser than a red laser. The damage can go unnoticed for a long period of time because it is painless. If shone directly into the eye, a laser pointer can cause instantaneous injury.
Sometimes, the damage can resolve over time but there are many instances when the damage is irreversible and permanent. Our eyes are highly developed to see in great detail and also in very low light, but these very qualities make them vulnerable to damage from light, as well. The already-concentrated light is further focused by the lens onto a small spot on the retina.
This causes a thermal burn in the retinal layers and may cause a scar to form.
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