Before you purchase a laser pointer online, you may find yourself wondering how far the beam can be seen. If you’re not familiar with different aspects of laser technology, this question might not have a clear answer. You may be wondering why do lasers look grainy sometimes and if that’s a bad sign of quality.
The lowest possible amount of light that can be seen with the naked eye in complete darkness is one ten-billionth of a watt per square meter. Urban light pollution, on the other hand, prevents one from viewing stars fainter than the North Star, which has an intensity of around four-billionths of a watt per square meter.
For perspective, the full moon is almost a million times brighter than one-thousandth of a watt per square meter. To put it in context, the midday sun shines at 1,000 watts per square meter which is about half a million times brighter than the moon.
All we need is an equation for calculating how quickly a laser beam spreads out as it travels through space. With that, we can use straightforward geometry to derive the diameter of the beam when it hits its target. Finally, we divide the power output of the laser by the area of the final lit spot and voila! — That’s how intense the laser is at destination.
When it comes to the way humans perceive light, this subject is far more complicated. For the purpose of this exercise, we’ll treat brightness and light intensity as synonymous.
How Far Can Your Pocket Laser Pointer Travel?
The power of a typical laser pointer is around 0.005 watts. If you aimed it directly at your eye from an arm’s length away, the tiny illuminated dot on your eyeball would be 30 times brighter than the midday sun because of the small beam’s tight passage. So, don’t try this at home or anywhere else.
Despite its modest width, the narrow beam will reach a long way. When viewed from a distance of 100 meters away, the beam of a red laser pointer is around 100 times broader and more brilliant than that of a 100-watt light bulb. The pointer would be as bright as a quarter moon from an airplane 40,000 feet up in the sky — assuming there are no clouds or smog. It would fade to roughly as bright as Sirius when viewed from the International Space Station.
How Far Can You See a Laser Beam?
The range and apparent distance of any laser are determined by a number of criteria. The output power (mW) will be first and foremost, followed by the color of the laser. Both are needed factors to determine how far a laser will be visible.
Unlike red light, green light scatters more in the atmosphere, which is why some amateur astronomers use green laser pens to point out planets or constellations in the night sky. The light scattering property ensures that you can project a beam up into the sky. It adds to the perception that green lasers are much more powerful than red ones.
Did you know that a green laser is 10 to 50 times more powerful than a red light laser at the same output power? Green lasers are considerably more efficient and noticeable in the presence of strong sunshine. They can also cover greater distances, which is why they’re so common on building sites.
Another factor to consider is beam focusing design characteristics, which are available on some laser models. You can pinpoint targets at close or long ranges with lasers that offer the option to thin or expand the beam, making it even better for long-range targeting. By condensing the beam, you will be able to see better both close up and at far away distances.
A 200mW green laser will be visible for up to 10 miles on a clear day, and a 1,000mW blue laser will be similarly visible.
Various environmental factors like fog and clouds can affect how far your beam will be visible, but as a general statement, you should anticipate over 10 miles of visibility with 200mW+ green lasers and 1,000mW+ blue lasers.
Do Lasers Go On Forever?
If you were to use a laser in space, then use the light would continue forever unless it hit something. Through, once you were far enough away you wouldn’t be able to see the light as it would be so spread out.
The same applies if you were to point a laser into space from earth. Some of the light would make it to space and continue until it collided into something else. But, some of the light would be potentially absorbed, blocked or scattered by the earths atmosphere.
That concept applies when you shine a laser into a mirror and it bounces off, some of the lasers energy is lost after each mirror it hits.
Lasers produce light that can be very focused. That’s why, over long distances, the light doesn’t normally spread out much. You only see a small spot when you use a laser pointer from across the room.
But if you were looking at the spot even further away, it would appear slightly bigger. If you go too far away though, eventually the light will spread out so much that it becomes undetectable to us human beings.
