# silly question: at what distance will a laser not burn objects?



## DisrupTer911

A green laser, capable of burning a hole in plastic or popping a balloon, lighting a match, etc etc...

At what distance could you shine it at something, without causing damage?

lets say you had a 1w blue that can burn holes in paper etc...at 100 yards will it burn paper?

at 200 yards?
at 1000 yards?

whats the safe distance where it can pass over objects without causing damage?


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## bshanahan14rulz

It depends on how it's focused, how well the optics are, the size of the optics, the size of the actual active emitting area on the laser cavity, and many other variables. Theoretically you could pop a balloon on the moon with a 5mW pointer. In practice, however, you won't burn things more than a few feet away. 

Best thing to do is to use proper safety precautions such as protective eyeware, and avoid shining it near sensitive equipment such as LCD screens, cameras, eyes, people in general. People have this weird habit of being afraid of things they don't understand, and they WILL assume that it is something illegal or wrong, even if you have taken all proper safety measures.

Just curious, whatcha planning?


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## DisrupTer911

so I shined a wicked lasers 1W blue into a forest, if it hits a tree, will it start to smolder?


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## bshanahan14rulz

Doubtful. Unless it was a forest of toothpicks a few inches away.


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## xul

Depends on the emissivity and reflectivity of the target.


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## fyrstormer

6 feet 3 inches. Basic law of physics. Amaze your friends when your high-powered laser bounces harmlessly off their retinas!

(not intended to be a factual statement)


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## pauljohan

DisrupTer911 said:


> so I shined a wicked lasers 1W blue into a forest, if it hits a tree, will it start to smolder?


dream to have the laser like this power:devil:


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## xul

"The _ignition temperature_ of _wood_ is usually given as about. 275 °C (525 °F)"


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## FRITZHID

there are many other variables as well, such as dust, ect in the air, color of the object, and humidity. to cause ignition of live wood (wet) @ 10+ ft, would require CO2 lasers @ 1kw for more than 3seconds. scorching would occur but actual ignition of damp wood is far harder. kiln dried wood (plywood) @ 35' with a 5kw CO2 took less than 1 sec to burst into flame, but @ 100' took longer than 5sec. this was with an unfocused beam strait out of the resonator @ aprox 2.5" dia.


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## Illum

xul said:


> Depends on the emissivity and reflectivity of the target.



that and factor in the wattage of the device and how much debris is floating in the atmosphere the beam is subjected to travel through.


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## samgab

I believe the calculation formula is: D = P
Where D is the Distance at which a laser will not burn objects
and P is the length of a piece of string.


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## egrep

Treat your laser like a firearm. But it's more difficult than that. Merely LOOKING at the dot can permanently damage vision and easily cause permanent blindness. Reflections can occur unexpectedly and the beam can end up going wildly unexpectly. Given your question it seems certain you do not have sufficient knowledge or experience to own and operate this device. 

NB: I own one and have it with me on vacation travel right now.


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## bshanahan14rulz

I'm always so excited to hear about people's new and interesting ideas of what a laser can be used for. I am also always disappointed to see that most of them just want to start fires from a distance, for no reason other than to presumably cause trouble or destroy others' property. Or trees.


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## xul

samgab said:


> I believe the calculation formula is: D = P
> Where D is the Distance at which a laser will not burn objects
> and P is the length of a piece of string.


Nah, I looked it up. It's D = P^1.


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## bshanahan14rulz

xul: you only raise P to the first power if the string used has been measured. Otherwise, you use P^0 for an arbitrarily chosen length of string, P. Units are in decibels.

So, to answer the main question, the distance is 1 decibels.


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## xul

bshanahan14rulz said:


> xul: you only raise P to the first power if the string used has been measured. Otherwise, you use P^0 for an arbitrarily chosen length of string, P. Units are in decibels.
> 
> So, to answer the main question, the distance is 1 decibels.


I came out with a furlong!


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## jessiemoore

The farther, the better. :nana:


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## CDR_Glock

DisrupTer911 said:


> A green laser, capable of burning a hole in plastic or popping a balloon, lighting a match, etc etc...
> 
> At what distance could you shine it at something, without causing damage?
> 
> lets say you had a 1w blue that can burn holes in paper etc...at 100 yards will it burn paper?
> 
> at 200 yards?
> at 1000 yards?
> 
> whats the safe distance where it can pass over objects without causing damage?



This is all theoretical:

A laser to which you refer is very much like a ballistic projectile. One must be aware of its path, any reflection and deviation from its path and what is behind its target.

The laser beam will just continue on a straight line. A laser needs to be collimated to focus the energy to burn something. You'd also have to be very still to focus it long enough to burn something. It would have to be mounted onto a tripod or other stable platform to prevent it from varying the focus. Any variance in degrees would cause it to deviate from a specific focal zone. 

However, it will cause still damage to the retina of anyone or any animal in its path. That's the danger of all lasers. Use outdoors is ILL-ADVISED and likely, not legal.


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## zeramant86

Typically for most lasers, this is nothing more than 8-10ft, to actually burn.

It depends on whether you have a multimode laser die or single mode.
Think MC-E compared to XR-E for throw

Single modes reach about 0.5w, whereas multimode will reach 1-1.5 easily.
The reason they burn better is due to a smaller spot. When you figure the general output of the laser, and the area that it covers, 0.5w properly focused will perform better than a 1.5 focused, unless you get into more complex optics.

Wavelength also comes into play as lower spectrum wavelengths tend to have more energy.
Basically a 405nm will burn better than a 445/450/532/650 in the visible range.

You will never burn anything at the moon, that's just silly. All laser diodes have a value listed as mRad, which tells how much the beam will expand over time. Optics can help this, but for practical purposes it will always exist.

Also, generally to pop balloons, you need at least a 30-50mw laser. To burn, no less than 200mw.

The most important thing when using lasers like this is to wear color blocking safety glasses for the laser you are using. Anything over 5mw can cause damage, and burning lasers can permanently blind you. They should be treated no different than a firearm.



Edit: Just saw this comment: Outdoor use is legal, when not aimed at a person, vehicle, animal, AIRCRAFT, etc. Use common sense with these lasers. Shining them at aircraft is very illegal and is almost always prosecuted/fined heavily.


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## CDR_Glock

DisrupTer911 said:


> A green laser, capable of burning a hole in plastic or popping a balloon, lighting a match, etc etc...
> 
> At what distance could you shine it at something, without causing damage?
> 
> lets say you had a 1w blue that can burn holes in paper etc...at 100 yards will it burn paper?
> 
> at 200 yards?
> at 1000 yards?
> 
> whats the safe distance where it can pass over objects without causing damage?



It will depend upon the power of that laser and the dispersion over a particular distance. If it is handheld, it is not going to be efficient in concentrating energy beyond some particular distance. It would have to be mounted onto a tripod to minimize that variance. Honestly, I doubt it would be effective to burn your paper beyond 10 yards.


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## Anders Hoveland

I have a 200 mW green laser pointer. It was a cheap Chinese-made one and I suspect it did not have any polarizer filters (which is dangerous because of the invissible high intensity infrared that comes out), so the burning power may have been more like 1125 mW. It could pop a black balloon at a distance of up to 8 cm after around 5 seconds, but much faster when the balloon was closer. It failed to pop white balloons, was a little more difficult to pop red balloons, and only popped green balloons when the laser was within 1cm. Trying to pop a moving balloon with the laser was just impossible (almost so), and certainly impossible from half a meter away.

The laser can burn black paper, but not very easily unless the paper is within 3 cm from the laser.

A one Watt laser is certainly not going to pose any unintentional damage risk to objects, although it is potentially very hazardous to humans not wearing protective filters over their eyes.


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## jasonalonzo

Lasers may not burn objects when its beam isn't intensified and have wavelenghts of 180–315 nm (UV-B, UV-C) at 650 nm lasers can burn or pop up balloons in other words this lasers is called Class 3B AEL.


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## zeramant86

I've always heard that lower wavelengths are better for burning, my recommendation for a burner is either a 1/2w 405nm, or a1.5w 445nm multimode. I've got a 1.8w 445, and it lights matches instantly almost. I haven't tried balloons yet tho.

I would stay away from anything lower than a 405nm, because of the additional risks with that range, and the cost/availability.


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