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#21
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More Consequences for Laser pranksters
On 2014.05.14, 16:24 , nospam wrote:
In article , Alan Browne wrote: Although I'm sure it happens, one never hears of idiots who shine lasers at cars. cops do it every single day. They use laser guns which produce a very diffused beam with a target circle of about 60'', not a high power point focused laser beam. actually it's much narrower than that. typical beam width is 3 feet at 1000 feet distance, which is a typical clocking distance for vehicles, if not a bit far. 3' is definitely wider than a point focused beam, but it doesn't mean it's entirely harmless. it's long term effects are not known. they're approved as class 1 devices, but they also come with warnings. it sends pulsed infrared light, whose *average* power is what is used to determine eye safety, not instantaneous power. The diffusion, if only 1 m at 300m reduces the power by many orders of magnitude v. a point. As usual you brought up a non-point to make ... no point at all. it does reduce the power but that's not what makes it considered to be safe. it's the low duty cycle which means it's average power is low. the actual pulses are quite strong. By the way, what really makes the police LIDAR's eyesafe is the very low laser power. Power levels at the laser aperture are on the order of 50 micro-Watts. On green pointers they are 10 - 100 mW. On red lasers (still eye safe ish) they are about 1 to 5 mW (often sold at higher than that, however). Another 200 - 2000 X less power for the police devices v. the device in question. Really - get your facts straight. -- "Big data can reduce anything to a single number, but you shouldn’t be fooled by the appearance of exactitude." -Gary Marcus and Ernest Davis, NYT, 2014.04.07 |
#22
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More Consequences for Laser pranksters
On 2014-05-14 21:03:30 +0000, Alan Browne
said: On 2014.05.14, 16:48 , Savageduck wrote: On 2014-05-14 20:10:39 +0000, Alan Browne said: On 2014.05.13, 22:42 , Savageduck wrote: On 2014-05-14 02:27:52 +0000, nospam said: In article , PeterN wrote: Although I'm sure it happens, one never hears of idiots who shine lasers at ca rs. cops do it every single day. They use laser guns which produce a very diffused beam with a target circle of about 60'', not a high power point focused laser beam. Also the law enforcement laser guns I am aware of do not use a light which is in the visible spectrum and is not likely to cause any retin al injury. Invisible lasers can cause a lot of damage too if not diffused. In our laser lab where I used to work (I was not part of that lab but occasionally worked with those engineers on some projects), they wore protective glasses - and it was not visible wavelengths). Per the Wikipedia article the police laser cone is about 1 m at 300 metres distance. Still enough diffusion to prevent eye damage. And of course the glass on the car would reflect a lot of it away from the driver's eyes as well as absorb some of the energy. Primary target is the front of the vehicle, usually the number plate, the diffused energy cone would cover the entire width and typically not be an issue with the windshield and any eyeballs behind it. Surely - but there's also the issue of missing the target and hitting innocent bystander eyeballs. Where would this hypothetical innocent bystander be? Standing on the shoulder of the highway? Perhaps moving faster than the traffic flow, on foot? Missing the target is very unusual, given the transitory nature of target acquisition and the diffused beam at typical ranges. It is sort of like shooting a tennis ball at 20 feet with a shotgun. -- Regards, Savageduck |
#23
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More Consequences for Laser pranksters
On 2014-05-14 21:16:58 +0000, Alan Browne
said: On 2014.05.14, 16:24 , nospam wrote: In article , Alan Browne wrote: Although I'm sure it happens, one never hears of idiots who shine lasers at cars. cops do it every single day. They use laser guns which produce a very diffused beam with a target circle of about 60'', not a high power point focused laser beam. actually it's much narrower than that. typical beam width is 3 feet at 1000 feet distance, which is a typica l clocking distance for vehicles, if not a bit far. 3' is definitely wider than a point focused beam, but it doesn't mean it's entirely harmless. it's long term effects are not known. they're approved as class 1 devices, but they also come with warnings. it sends pulsed infrared light, whose *average* power is what is used to determine eye safety, not instantaneous power. The diffusion, if only 1 m at 300m reduces the power by many orders of magnitude v. a point. As usual you brought up a non-point to make ... no point at all. it does reduce the power but that's not what makes it considered to be safe. it's the low duty cycle which means it's average power is low. the actual pulses are quite strong. By the way, what really makes the police LIDAR's eyesafe is the very low laser power. Power levels at the laser aperture are on the order of 50 micro-Watts. On green pointers they are 10 - 100 mW. On red lasers (still eye safe ish) they are about 1 to 5 mW (often sold at higher than that, however). Another 200 - 2000 X less power for the police devices v. the device in question. Really - get your facts straight. Yup! -- Regards, Savageduck |
#24
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More Consequences for Laser pranksters
On 2014.05.14, 17:17 , Savageduck wrote:
On 2014-05-14 21:03:30 +0000, Alan Browne said: On 2014.05.14, 16:48 , Savageduck wrote: On 2014-05-14 20:10:39 +0000, Alan Browne said: On 2014.05.13, 22:42 , Savageduck wrote: On 2014-05-14 02:27:52 +0000, nospam said: In article , PeterN wrote: Although I'm sure it happens, one never hears of idiots who shine lasers at ca rs. cops do it every single day. They use laser guns which produce a very diffused beam with a target circle of about 60'', not a high power point focused laser beam. Also the law enforcement laser guns I am aware of do not use a light which is in the visible spectrum and is not likely to cause any retin al injury. Invisible lasers can cause a lot of damage too if not diffused. In our laser lab where I used to work (I was not part of that lab but occasionally worked with those engineers on some projects), they wore protective glasses - and it was not visible wavelengths). Per the Wikipedia article the police laser cone is about 1 m at 300 metres distance. Still enough diffusion to prevent eye damage. And of course the glass on the car would reflect a lot of it away from the driver's eyes as well as absorb some of the energy. Primary target is the front of the vehicle, usually the number plate, the diffused energy cone would cover the entire width and typically not be an issue with the windshield and any eyeballs behind it. Surely - but there's also the issue of missing the target and hitting innocent bystander eyeballs. Where would this hypothetical innocent bystander be? Standing on the shoulder of the highway? Perhaps moving faster than the traffic flow, on foot? Missing the target is very unusual, given the transitory nature of target acquisition and the diffused beam at typical ranges. It is sort of like shooting a tennis ball at 20 feet with a shotgun. It's all moot (given the actual facts), but anyone could be firing the laser at anyone anywhere. The combinations of: - very low power (50 micro-watts) - pulse rate/duty cycle - diffusion - reflection off of windshields and some absorption - very short "event" cycle (1/4 of a second or so). Make the power on eyes issue completely moot - so you have to wonder why nofacts brought it up in the context of a much more powerful CW laser... -- "Big data can reduce anything to a single number, but you shouldn’t be fooled by the appearance of exactitude." -Gary Marcus and Ernest Davis, NYT, 2014.04.07 |
#25
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More Consequences for Laser pranksters
In article , Alan Browne
wrote: Per the Wikipedia article the police laser cone is about 1 m at 300 metres distance. Still enough diffusion to prevent eye damage. And of course the glass on the car would reflect a lot of it away from the driver's eyes as well as absorb some of the energy. the windshield reflects very little and lidar can be used through glass although it usually is not. It would reflect a good chunk. No figures here, but lasers oblique to glass (most windshields are at an angle) do reflect quite a bit of their energy. not that much. most goes through it. the risk is low because the average power is low due to the pulsing, not the diffusing. it has a very, very low duty cycle. A combination to be sure. But the comparison in this discussion is with a laser pointer without a diffuser or scintillator. As an example, if the laser made a 1mm diameter circle without a diffuser and then that is spread to 1m diameter at 300 metres with a diffuser, then the surface power would be 1,000,000 times lower where the laser hit someone's eye. except that the power of a lidar gun transmitter is significantly higher than a pocket laser pointer. OTOH, a typical pulse rate is 1 kHz with a duty cycle of 30 ns. Doesn't sound like much - OTOH, that's 30X more power than what is delivered due to diffusion. To say the diffusion is not significant is plain silly. it's not the only part. |
#26
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More Consequences for Laser pranksters
In article , Alan Browne
wrote: have you even used a lidar gun? My experience is in pulsed, CW and FM/CW radar where I worked mainly in embedded s/w and test s/w for those systems. We also (the aforementioned lab) built a pulsed laser for obstacle detection (proof of concept) which I've used in demos (in Japan). That never entered a product development period, alas. Eventually our radar work would be in competition with a German co. who used lasers (and reasonably well at terrifically high cost and weight) for that purpose. And yes, with some of the radars we made, safety was indeed an issue (the computation always accounted for pulse rate, duty cycle, area of exposure, power (and at least with scanning devices) scan rates. You could say I'm quite familiar with both. that helps, but if you actually used a lidar gun to clock cars you will see that the windshield is not as reflective as you claim. |
#27
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More Consequences for Laser pranksters
In article 2014051414174666962-savageduck1@REMOVESPAMmecom,
Savageduck wrote: Primary target is the front of the vehicle, usually the number plate, the diffused energy cone would cover the entire width and typically not be an issue with the windshield and any eyeballs behind it. Surely - but there's also the issue of missing the target and hitting innocent bystander eyeballs. Where would this hypothetical innocent bystander be? Standing on the shoulder of the highway? Perhaps moving faster than the traffic flow, on foot? the driver of the vehicle for one, as well as passengers. Missing the target is very unusual, given the transitory nature of target acquisition and the diffused beam at typical ranges. It is sort of like shooting a tennis ball at 20 feet with a shotgun. the beam hitting places other than the license plate or headlights is quite common. that's what lidar detectors pick up (as well as scatter). |
#28
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More Consequences for Laser pranksters
In article 2014051414051812228-savageduck1@REMOVESPAMmecom,
Savageduck wrote: it does reduce the power but that's not what makes it considered to be safe. it's the low duty cycle which means it's average power is low. the actual pulses are quite strong. have you even used a lidar gun? Have you? I have. sure have, as well as many radar guns. cops aren't the only ones who use them, and they don't generally know what goes on inside at a technical level either. |
#29
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More Consequences for Laser pranksters
In article , Alan Browne
wrote: By the way, what really makes the police LIDAR's eyesafe is the very low laser power. Power levels at the laser aperture are on the order of 50 micro-Watts. the average power is low because of the duty cycle. the actual power of the pulse is 1,000,000 times higher, at about 50 *watts*. kustom prolaser: https://www.google.com/patents/US5221956 The gallium-arsenide laser produces laser energy having a wave length of 905 nanometers with a peak power output of approximately 50 watts and a 30 to 50 nanosecond pulse width. laser atlanta: https://www.google.com/patents/US6108071 In a preferred embodiment, the emitter is a GaAs type, producing laser radiation having a wavelength of about 905 nanometers, with a peak power output of approximately 50 watts and a 30-50 nanosecond pulse width. On green pointers they are 10 - 100 mW. On red lasers (still eye safe ish) they are about 1 to 5 mW (often sold at higher than that, however). the difference is that laser pointers are a continuous beam, not pulsed. Another 200 - 2000 X less power for the police devices v. the device in question. other way around. lidar guns have substantially higher power laser diodes. Really - get your facts straight. they are correct. |
#30
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More Consequences for Laser pranksters
In article , Alan Browne
wrote: It's all moot (given the actual facts), but anyone could be firing the laser at anyone anywhere. The combinations of: - very low power (50 micro-watts) 50 watts, not 50 micro-watts. see links in other post. - pulse rate/duty cycle - diffusion yes to both - reflection off of windshields and some absorption negligible. - very short "event" cycle (1/4 of a second or so). the duration is typically longer. Make the power on eyes issue completely moot - so you have to wonder why nofacts brought it up in the context of a much more powerful CW laser... then why don't you tell that to the lidar gun makers who include safety warnings. they are classified as safe, but that doesn't mean they can't cause damage. it's that they probably won't based on what is currently known. |
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