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07082012, 08:13 PM  #1  
 
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I want to test how the laser looks from a distance. Can pointing directly on someone from 1Km with 200mw Green laser do any damage? (Lets say I mesured the distance with Google earth before trying). Same for 1w Blue laser?  
07082012, 08:24 PM  #2  
 
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Depends on the power density! If you have a large beam, and a large divergence it will likely not exceed the MPE (maximum permissible exposure) If you have a really small beam with an amazing divergence it will likely exceed the MPE. Without knowing more about the lasers I cannot say.  
07082012, 08:35 PM  #3  
 
Class 3B Laser Join Date: Sep 2007 Location: Southern California
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Google NOHD.
__________________ DNA works in mysterious ways.  
07082012, 08:36 PM  #4  
 
Class 3R Laser Join Date: Jul 2010 Location: Olomouc, Czech Republic
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Yep .. depends on the optics used.
 
07082012, 10:59 PM  #5  
 
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Interesting. If that's correct you can keep staring at even the most powerful handheld visible lasers if the dot is larger than say 80cm (1mW/cm^2 @ 5W). What's the catch? I've never looked at my 1100mW's dot indoors without goggles even while defocused but this is getting me tempted. What about the whole blue light hazard thing?
__________________ 405nm: NewWish (29.1mW avg5mW rtd)  Dilda (81.5mW avg200mW rtd)  501B by Blord (633mW pk) low 445nm: C6 from Survival Lasers (1351mW pk1289mW avg1100mW rtd) high 450nm: NewWish (12.6mW pk5mW rtd)  Dominator by Blord (3010mW pk2779mW avg during 5min) 462nm: 501B by Atomic (1507mW avg) 473nm: BWB10OEM labby by CNI (10mW rtd) 520nm: MXDL pen by DTR (31.6mW pk28.8mW avg) 532nm: NewWish (28.6mW pk26.8mW avg10mW rtd)  Dapper (30.3mW pk)  Classic (120.0mW pk103.1mW avg100mW rtd)  "The Green Box" by Atomic (176.7mW pk140.0mW avg) 589nm: Spartan from Dragon Lasers (58.4mW pk37mW avg50mW rtd) 632.8nm: HeNe pointer by Atomic (0.68mW rtd) 635nm: NewWish (4.6mW avg5mW rtd) 638nm: Classic from Lazerer (409.3mW pk389.4mW avg415mW rtd) 650nm: NewWish (10.6mW pk5mW rtd)  Dilda (216.3mW avg200mW rtd) 685nm: laserinabox by Atomic (30.4mW pk29.3mW avg)  501B by Atomic (32.4mW avg) 780nm: module (2.7mW avg5mW rtd) 808nm: Classic modded from a 532nm (162mW avg) 850nm: module (8.8mW avg7mW rtd) 980nm: NewWish (81mW pk5mW rtd)  2nd line around 490nm 5W Ophir LPM HV: Flyback, Plasma Speaker, The Arcsynth and SSTC  
07082012, 11:14 PM  #6  
 
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Ok. I did some research and learning. And here are my conclusions: Let’s talk about a super high quality laser as an example, with the following spec: Green laser 200 mw Beam diameter  1mm (Typically it is 1.5mm and above) Divergence 0f 0.5mrad (Typically it is 1 and above for Green laser) 1000 Meter distance. Assuming air do not make any loses Calculation will be done in cm: Diameter of the beam will be 100000*tan(0.0005)+0.1 = 50cm Beam coverage area: (50/2)^2*PI=1963 cm2 (Assuming a round beam, which is the most powerful) Power per cm2: 200mw/1963cm2=0.1mw/cm2 According to the following graph (File:IEC60825 MPE W s.png  Wikimedia Commons) This amount of power is completely safe and in fact you can look at the laser directly without any problems. Blue laser 1000 mw Beam diameter  1mm (Typically it is 1.5mm and above) Divergence 0f 0.4mrad (Typically it is 1 and above for Blue laser) 1000 Meter distance. Assuming air do not make any loses Calculation will be done in cm: Diameter of the beam will be 100000*tan(0.0004)+0.1 = 40cm Beam coverage area: (40/2)^2*PI=1256 cm2 (Assuming a round beam, which is the most powerful) Power per cm2: 1000mw/1256cm2=0.8mw/cm2 Still, you can look at it from this distance without any damage. For fun, here is the calculation for a distance of 5m: Green laser 200 mw Beam diameter  1mm (Typically it is 1.5mm and above) Divergence 0f 0.5mrad (Typically it is 1 and above for Green laser) 5 Meter distance. Assuming air do not make any loses Diameter of the beam will be 500*tan(0.0005)+0.1 = 0.35cm Beam coverage area: (0.35/2)^2*PI=0.096 cm2 (Assuming a round beam, which is the most powerful) Power per cm2: 200mw/0.096cm2=2078mw/cm2 SUPER DANGEROUS. IMMEDIATE DAMAGE!!!!  
07082012, 11:19 PM  #7  
 
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Hi Atomicrox. I thought I miscalculated something, so I delete the message. But eventually it was ok. I added a short distance calculation. There is a huge difference as you can see. Short distance is very dangerous.  
07082012, 11:51 PM  #8  
 
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Using these numbers we can calculate approximately how much light is entering the eye. According to this: The Pupils  Clinical Methods  NCBI Bookshelf The minimum pupil diameter is 24mm and maximum is 48mm. Using the average of these numbers gets us 3mm min. and 6mm max. Then the total amount of light (mW) entering the eye would be the power per cm^2 you calculated above multiplied by the area of the pupil. Green laser: 0.1mW/cm2 = 0.01mW/mm2 Minimum pupil diameter 3mm (radius 1.5mm): 3.14 x 1.5^2 x 0.1 > 7.06 x 0.01 = 0.07mW total entering the eye Maximum pupil diameter 6mm (radius 3mm): 3.14 x 3^2 x 0.1 > 28.26 x 0.1 = 0.28mW total entering the eye Blue laser: 0.8mW/cm2 = 0.08mW/mm2 Minimum pupil diameter 3mm (radius 1.5mm): 7.06 x 0.08 = 0.56mW total entering the eye Maximum pupil diameter 6mm (radius 3mm): 28.26 x 0.08 = 2.26mW total entering the eye If we use the figure of 8mm diameter (4mm radius) for maximum pupil dilation that results in: Maximum of 0.5mW entering the eye from 200mW green laser Maximum of 4.01mW entering the eye from 1000mW blue laser Considering the fact that the lens of the eye focuses light on the retina, there still is a chance of some damage with higher power lasers. At the very least it would not be comfortable to look at with darkadapted eyes. Does this seem correct?
__________________ DNA works in mysterious ways. Last edited by RA_pierce; 07092012 at 12:00 AM.  
07092012, 12:13 AM  #9  
 
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Unfortunately, you have a mistake in a factor of 10. 0.1mw/cm2 = 0.001mw/mm2 (You have to divide by 100) Lets stay in cm. According to Wikipedia, when the pupil is max opened it is 49 mm. Let’s take 9 mm which is 0.9cm. So the power entering the eye with blue laser is: (0.9/2)^2*pi*0.8=0.5mw.  
07092012, 12:21 AM  #10  
 
Class 3B Laser Join Date: Sep 2007 Location: Southern California
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So at 1km distance it's relatively safe to view the beam directly. Might I ask what you plan to do with this information?
__________________ DNA works in mysterious ways.  
07092012, 12:31 AM  #11  
 
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I was just curious to see how a laser looks from a large distance. Can it be seen? Can it be seen from 5 km? All this laser stuff is not very practical. It is just pure fun to experiment with it.  
07092012, 12:40 AM  #12  
 
Class 3B Laser Join Date: Sep 2007 Location: Southern California
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There are some videos on youtube of people shining lasers over a few miles (not sure exactly how far). I've been able to put a spot on a mountain about 10 miles (about 16km) from where I live. It was just visible with a telephoto lens on my camera and good visibility (it's usually smoggy). The laser was >650mW 532nm with a 10x beam expander. At that distance the beam should have been about 2 meters across. I'm sure that if someone was on the other end they would have had no problem seeing it.
__________________ DNA works in mysterious ways.  
07092012, 01:52 PM  #13  
 
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This is also a worst case calculation so in reality lasers should be a lot safer... This is leading me to believe long range/defocused laser danger is highly overestimated around these forums and by the media in general. I'd really like one of the more experience members to shine a light here, especially if we're missing something!
__________________ 405nm: NewWish (29.1mW avg5mW rtd)  Dilda (81.5mW avg200mW rtd)  501B by Blord (633mW pk) low 445nm: C6 from Survival Lasers (1351mW pk1289mW avg1100mW rtd) high 450nm: NewWish (12.6mW pk5mW rtd)  Dominator by Blord (3010mW pk2779mW avg during 5min) 462nm: 501B by Atomic (1507mW avg) 473nm: BWB10OEM labby by CNI (10mW rtd) 520nm: MXDL pen by DTR (31.6mW pk28.8mW avg) 532nm: NewWish (28.6mW pk26.8mW avg10mW rtd)  Dapper (30.3mW pk)  Classic (120.0mW pk103.1mW avg100mW rtd)  "The Green Box" by Atomic (176.7mW pk140.0mW avg) 589nm: Spartan from Dragon Lasers (58.4mW pk37mW avg50mW rtd) 632.8nm: HeNe pointer by Atomic (0.68mW rtd) 635nm: NewWish (4.6mW avg5mW rtd) 638nm: Classic from Lazerer (409.3mW pk389.4mW avg415mW rtd) 650nm: NewWish (10.6mW pk5mW rtd)  Dilda (216.3mW avg200mW rtd) 685nm: laserinabox by Atomic (30.4mW pk29.3mW avg)  501B by Atomic (32.4mW avg) 780nm: module (2.7mW avg5mW rtd) 808nm: Classic modded from a 532nm (162mW avg) 850nm: module (8.8mW avg7mW rtd) 980nm: NewWish (81mW pk5mW rtd)  2nd line around 490nm 5W Ophir LPM HV: Flyback, Plasma Speaker, The Arcsynth and SSTC  
07102012, 03:08 PM  #14  
 
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Yep. I also think that the pupil computation is irrelevant. Here is the link to the graph I used as reference, in case someone missed it. According to the author of the graph, it is based on IEC 60825 formulas http://commons.wikimedia.org/wiki/Fi...25_MPE_W_s.png Last edited by opr; 07102012 at 03:09 PM.  
07102012, 03:45 PM  #15  
 
Class 3B Laser Join Date: Sep 2007 Location: Southern California
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I think that a number for how much light is entering the eye is easier to relate to than a number for power density. Just meant to give a different perspective rather than just going by the charts.
__________________ DNA works in mysterious ways.  
07102012, 07:59 PM  #16  
 
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Laser Pointer Experiment Free download. Laser Visuals  Scanguard laser show analysis software : Lite Version  
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