Welcome to Laser Pointer Forums! If you are looking for a laser you may want to check out the Laser Company Top Sites List. The link will open in a new window for your convenience.

Colorful 2018, Colorful Laser Power Meter
 Laser Pointers Is an unfocused 4W laser do dangerous at 5 meters?

LPF Laser Pointer Company Database (link opens new window)

11-01-2016, 03:18 PM #17
 Super Moderator Join Date: Jan 2014 Location: Qatar, land of the hot footed. Posts: 9,552 Rep Power: 1721814
Super Moderator

Join Date: Jan 2014
Location: Qatar, land of the hot footed.
Posts: 9,552
Rep Power: 1721814
Re: Is an unfocused 4W laser do dangerous at 5 meters?

At some power level a flashlight should be able to produce a power density strong enough to do the same damage of 5mw laser could do, if focused upon long enough. It cannot focus down to as fine a spot, but no doubt a power density equal to that can be achieved, but at how much power when coming from a uniform 45 degree spread, for example.

__________________

Attention new brothers of the collimated light!

Newbie advice: Please take the time to first make an introduction in the Welcome section before posting questions: - https://laserpointerforums.com/f37

Divergence to spot size calc: - 1 mRad is about .057 degrees which expands to be very roughly ~10% the diameter of the moon or sun at their distances.

Divergence Calculator: pseudonomen137's JScript mRad Calculator - Measure your lasers beam dia. at 1 foot & then 20'.

Online calc. to determine spot intensity at different mRad's & powers: http://tinyurl.com/divergence-calculator

Laser Power Density Calculator: Laser Power Density Calculator - Ophir

Build a beam expander to reduce divergence: http://tinyurl.com/BeamExpander

University YAG Project The Professor's Homebuilt Lasers Site - YAG Lasers

YAG Power Calc. Laser Peak Power Calculator - Ophir

Angular Size Calculator; use with diode angle of radiation spec. for lens dia. at FL: Angular Size Calculator

RHD's Relative Brightness vs Wavelength Calc: https://tinyurl.com/RHD-brightness

High Current Pulse Diode Drivers: https://tinyurl.com/ya7whuk3

11-01-2016, 05:32 PM #18
 Member Join Date: Jun 2010 Location: SF Bay Area, California, USA Posts: 41 Rep Power: 0
bluestars
Member

Join Date: Jun 2010
Location: SF Bay Area, California, USA
Posts: 41
Rep Power: 0
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by Cyparagon The eye is designed to focus onto the retina. Since the parallel nature of a laser beam represents an object a very, very long distance away, the resulting spot on the retina is potentially very, very small. This concentrates the power and therefore greatly increases the danger as compared with an LED.
This definitely seems to be true for a laser beam, but the output of a multimode laser diode without a focusing lens is not a beam - it is a cone with a high divergence, just like a power LED. If the rays were already parallel, we wouldn't need a collimating optical assembly to form a laser beam.

If you add a lens to the situation, I strongly agree that lasers represent a much more significant eye hazard than high power LEDs. However, without a lens, I still think my analysis stands.

I don't want to claim that 4mW is above or below MPE for any particular wavelength and exposure time. I am not a laser safety officer and I'm really engaging in this discussion for my own edification. I believe the OP's question has been well answered by the members who say "don't do that".

Interestingly (and a bit off topic), since all optical processes must be reversible, it's actually impossible to focus light from any real light source to a point. Instead, the best you can do is an (increasingly small) image of the light source. XKCD explains well:
https://what-if.xkcd.com/145/
__________________
500mw 405nm eBay labbie
1W 445nm built by yobresal
Uniphase-Cyonics 2201-25ML 488nm+ Argon
Sanwu 304 80mW 532nm
Gammax 1A415 1mW 632.8nm HeNe
LPC-826 250mW 658nm labbie (waiting for heat sink and driver)

11-01-2016, 05:50 PM #19
 Class 4 Laser Join Date: Feb 2008 Location: Yellowknife, NT, Canada Posts: 9,132 Rep Power: 1258493
diachi
Class 4 Laser

Join Date: Feb 2008
Posts: 9,132
Rep Power: 1258493
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by bluestars This definitely seems to be true for a laser beam, but the output of a multimode laser diode without a focusing lens is not a beam - it is a cone with a high divergence, just like a power LED. If the rays were already parallel, we wouldn't need a collimating optical assembly to form a laser beam. If you add a lens to the situation, I strongly agree that lasers represent a much more significant eye hazard than high power LEDs. However, without a lens, I still think my analysis stands. I don't want to claim that 4mW is above or below MPE for any particular wavelength and exposure time. I am not a laser safety officer and I'm really engaging in this discussion for my own edification. I believe the OP's question has been well answered by the members who say "don't do that".
Except, even unfocused laser light is still coherent and will still be focused to a point at the back of your eye. Read up on "coherent light". You are misunderstanding the meaning of parallel in this context. Your eye adds the lens to the situation.
__________________

355nm | Bruker SmartBeam | Q-Switched Nd:YAG | Awaiting Arrival
405nm | Banggood LT-850 | 50mW Metered | Review Unit | >>Review<<
445nm | Sanwu Laser Pocket Series | 400mW Metered
445nm | NDB7242E Pen Build | 60mW Metered | >>Build Thread<<
450nm | LaserPointerStore - Thor H2 | 1.6W Metered | Review Unit | >>Review<<
473nm | B&W Tek BWB-10-OEM |
488nm | Spectra Physics 163 Argon | ~30mW Metered |
495nm | Laser66 Pen Build | WIP
515nm | PL515 Pen Build | 50mW | >>Build Thread<<
520nm | Laserlands 520 5mW | 3mW Metered | Review Unit | >>Review<<
532nm | Gearbest 303 Pointer | 50mW Metered
532nm | Gearbest JD-850 Pointer | 30mW Metered |
633nm | HeNe | 6mW
633nm | Spectra Physics 155 HeNe | <1mW >>Thread<<
650nm | Sanwu Laser Pocket Series | 200mW Metered
808nm | Melles Griot 532nm Lab Unit | No Crystals >10W

B&W Tek Spectrometer
LaserBee 2.5W USB LPM

Last edited by diachi; 11-01-2016 at 05:52 PM.

11-01-2016, 06:11 PM #20
 Member Join Date: Jun 2010 Location: SF Bay Area, California, USA Posts: 41 Rep Power: 0
bluestars
Member

Join Date: Jun 2010
Location: SF Bay Area, California, USA
Posts: 41
Rep Power: 0
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Coherent light just means that the light waves are in-phase and have the same frequency:
https://en.wikipedia.org/wiki/Coherence_(physics)

The laser diode rays are definitely not parallel (or even nearly so) or the size of the spot on my wall would not be ~1 inch at a few inches and 42 inches at 3 feet!

If I look at an active laser diode from 10m away with no optics near the face of the diode, my eye will not be able to somehow focus all the light that didn't hit my pupil down to a single point. However, I have a hypothesis for the relevant difference between power LEDs and laser diodes here: the light that does hit my pupil will be relatively parallel, because the ratio between the size of the diode's emitting area (on the order of 100µm²) and the distance to me is quite large, so it will be focused to a pretty small region. An LED has an emitter size of something more like 10mm² (2 orders of magnitude larger), which means that the light rays will be "less" parallel. I'm not sure if that makes any sense from an optical point of view, and I don't have any drawing tools at work so I can't quite work the problem. If anyone could chime in to help me understand the relevant difference between uncollimated laser light and LED emitters, I'd much appreciate it!
__________________
500mw 405nm eBay labbie
1W 445nm built by yobresal
Uniphase-Cyonics 2201-25ML 488nm+ Argon
Sanwu 304 80mW 532nm
Gammax 1A415 1mW 632.8nm HeNe
LPC-826 250mW 658nm labbie (waiting for heat sink and driver)

11-01-2016, 09:32 PM #21
 Class 4 Laser Join Date: Sep 2007 Location: Wisconsin Posts: 9,315 Rep Power: 385035
Cyparagon
Class 4 Laser

Join Date: Sep 2007
Location: Wisconsin
Posts: 9,315
Rep Power: 385035
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by bluestars Interestingly (and a bit off topic), since all optical processes must be reversible, it's actually impossible to focus light from any real light source to a point. Instead, the best you can do is an (increasingly small) image of the light source.
That's not off topic at all. It is another way of stating the dangers of laser diodes. The emitting area ("image") of your typical high power LED is several mm or even several cm. By contrast, a typical laser diode has an emitting area about 2 µm for single mode, and 15-150µm for multimode. In a way, you answered your own question.

Even if we could somehow get an emitting area approaching size zero, the focus would still be limited by diffraction, and is roughly equivalent to the wavelength of light. ie 405nm light cannot possibly focus onto a smaller diameter than 405nm.

Quote:
 Originally Posted by bluestars The laser diode rays are definitely not parallel
Except they are, and as you alluded to it's because of this: the rays not entering your eye can be ignored... because they're not entering your eye. The EFFECTIVE angle is from one side of the pupil to the other. This is still very near parallel.
__________________
A problem well stated is a problem half solved.

Last edited by Cyparagon; 11-01-2016 at 09:35 PM.

11-01-2016, 09:43 PM #22
 Member Join Date: Jun 2010 Location: SF Bay Area, California, USA Posts: 41 Rep Power: 0
bluestars
Member

Join Date: Jun 2010
Location: SF Bay Area, California, USA
Posts: 41
Rep Power: 0
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by Cyparagon Even if we could somehow get an emitting area approaching size zero, the focus would still be limited by diffraction, and is roughly equivalent to the wavelength of light. ie 405nm light cannot possibly focus onto a smaller diameter than 405nm.

Quote:
 Originally Posted by Cyparagon You're wrong. And I'll tell you why. It's because the rays not entering your eye can be ignored... because they're not entering your eye. The EFFECTIVE angle is from one side of the pupil to the other. This is still very near parallel.
That makes sense, but why is this different for an LED? The rays that manage to hit my eye should still be pretty parallel, right?
__________________
500mw 405nm eBay labbie
1W 445nm built by yobresal
Uniphase-Cyonics 2201-25ML 488nm+ Argon
Sanwu 304 80mW 532nm
Gammax 1A415 1mW 632.8nm HeNe
LPC-826 250mW 658nm labbie (waiting for heat sink and driver)

11-01-2016, 10:00 PM #23
 Class 4 Laser Join Date: Feb 2008 Location: Yellowknife, NT, Canada Posts: 9,132 Rep Power: 1258493
diachi
Class 4 Laser

Join Date: Feb 2008
Posts: 9,132
Rep Power: 1258493
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by bluestars That makes sense, but why is this different for an LED? The rays that manage to hit my eye should still be pretty parallel, right?

Light from an LED is going all over the place, essentially traveling in different directions, it's an unorganized jumble with a wide range of wavelengths (Different wavelengths will focus slightly differently due to varying indices of refraction at different wavelengths).

Light from a laser is coherent, all traveling in the same direction, organized and for all intents and purposes "parallel". All of the energy is also contained in one narrow wavelength "band".

https://en.wikipedia.org/wiki/Diffra...limited_system - The Wiki article talks briefly about lasers, but covers more than just lasers.
__________________

355nm | Bruker SmartBeam | Q-Switched Nd:YAG | Awaiting Arrival
405nm | Banggood LT-850 | 50mW Metered | Review Unit | >>Review<<
445nm | Sanwu Laser Pocket Series | 400mW Metered
445nm | NDB7242E Pen Build | 60mW Metered | >>Build Thread<<
450nm | LaserPointerStore - Thor H2 | 1.6W Metered | Review Unit | >>Review<<
473nm | B&W Tek BWB-10-OEM |
488nm | Spectra Physics 163 Argon | ~30mW Metered |
495nm | Laser66 Pen Build | WIP
515nm | PL515 Pen Build | 50mW | >>Build Thread<<
520nm | Laserlands 520 5mW | 3mW Metered | Review Unit | >>Review<<
532nm | Gearbest 303 Pointer | 50mW Metered
532nm | Gearbest JD-850 Pointer | 30mW Metered |
633nm | HeNe | 6mW
633nm | Spectra Physics 155 HeNe | <1mW >>Thread<<
650nm | Sanwu Laser Pocket Series | 200mW Metered
808nm | Melles Griot 532nm Lab Unit | No Crystals >10W

B&W Tek Spectrometer
LaserBee 2.5W USB LPM

Last edited by diachi; 11-01-2016 at 10:03 PM.

11-02-2016, 02:07 AM #24
 Class 4 Laser Join Date: Sep 2007 Location: Wisconsin Posts: 9,315 Rep Power: 385035
Cyparagon
Class 4 Laser

Join Date: Sep 2007
Location: Wisconsin
Posts: 9,315
Rep Power: 385035
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by bluestars but why is this different for an LED? The rays that manage to hit my eye should still be pretty parallel, right?
The emitter size dictates the minimum focus size. You cannot focus the beam from a 5mm LED source any smaller than 5mm, no matter your optics. Google ray diagrams to understand why. The ray coming from one edge of the LED will be focused to a different spot than the ray coming from the other edge.
__________________
A problem well stated is a problem half solved.

11-02-2016, 05:33 AM #25
 Super Moderator Join Date: Jan 2014 Location: Qatar, land of the hot footed. Posts: 9,552 Rep Power: 1721814
Super Moderator

Join Date: Jan 2014
Location: Qatar, land of the hot footed.
Posts: 9,552
Rep Power: 1721814
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Cyparagon,

The thread is now off of what I believe is the original heart of the question, at least, just my interest in this subject; how much power from an incoherent light source such as a high power flashlight LED is needed to equal the power density an unfocused (edit: except by the eye) laser diode can produce within the eye at 5mw of power, using the originally stated parameters, less the 1000 lumen stated limit? Assume a 3000 um x 3000 um LED emitter such as the SST90 has.

http://www.luminus.com/products/Lumi..._Datasheet.pdf

Is the power output of the 2000+ lumen flashlight SST90 LED at a 5 meter distance below the power density produced in the eye from the output from an unfocused 5mw laser diode at that same distance with a small 100x10um emitter, for example? I suppose I could use a smaller emitter size for a 5mw laser diode, certainly when single mode, but for example, I think it is close enough. Although when referencing this LED, the angles are different than a laser diodes radiation angle, so all things are not equal and require further number crunching than the simple example in the question given earlier. Also, I will have to reference a specific laser diodes characteristics if comparing with a specific flashlight LED, I think.

Quote:
 Originally Posted by bluestars I'm also curious - what makes bright flashlights safe but (unfocused) laser diodes dangerous? Assume a 1000 lumen flashlight with a 15 degree spot, 75% of power in the spot...
A rough mental comparison of the emitter sizes and power levels alone if the radiation angles are similar to one another is an easy answer, but I will crunch some numbers for a specific 5mw laser diode for both fast and slow axis to be sure and post later.
__________________

Attention new brothers of the collimated light!

Newbie advice: Please take the time to first make an introduction in the Welcome section before posting questions: - https://laserpointerforums.com/f37

Divergence to spot size calc: - 1 mRad is about .057 degrees which expands to be very roughly ~10% the diameter of the moon or sun at their distances.

Divergence Calculator: pseudonomen137's JScript mRad Calculator - Measure your lasers beam dia. at 1 foot & then 20'.

Online calc. to determine spot intensity at different mRad's & powers: http://tinyurl.com/divergence-calculator

Laser Power Density Calculator: Laser Power Density Calculator - Ophir

Build a beam expander to reduce divergence: http://tinyurl.com/BeamExpander

University YAG Project The Professor's Homebuilt Lasers Site - YAG Lasers

YAG Power Calc. Laser Peak Power Calculator - Ophir

Angular Size Calculator; use with diode angle of radiation spec. for lens dia. at FL: Angular Size Calculator

RHD's Relative Brightness vs Wavelength Calc: https://tinyurl.com/RHD-brightness

High Current Pulse Diode Drivers: https://tinyurl.com/ya7whuk3

Last edited by Alaskan; 11-02-2016 at 06:39 AM.

11-04-2016, 08:04 PM #26
 Member Join Date: Jun 2010 Location: SF Bay Area, California, USA Posts: 41 Rep Power: 0
bluestars
Member

Join Date: Jun 2010
Location: SF Bay Area, California, USA
Posts: 41
Rep Power: 0
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Sam's laser FAQ has a good page discussing laser safety, although it almost entirely deals with collimated beams. It does say this:
"A collimated beam is the most dangerous since it can be focused to a microscopic spot on the retina. A highly divergent beam - even a high power one - is much less of a hazard unless something is very close to the source."
Sam's Laser FAQ - Laser Safety

Staring at an active laser diode certainly seems like a bad idea.

Quote:
 Originally Posted by Cyparagon The emitter size dictates the minimum focus size. You cannot focus the beam from a 5mm LED source any smaller than 5mm, no matter your optics. Google ray diagrams to understand why. The ray coming from one edge of the LED will be focused to a different spot than the ray coming from the other edge.
I must be misunderstanding what you mean by "focus the beam". The moon is about 2000 miles in diameter, but my eye focuses light from it down to between 1mm² and 1000mm² on my retina. Of course, that's not _all_ the light from the moon (since most of it didn't hit my pupil) but I am certainly able to focus what does hit my eye to something smaller than 2000 miles in diameter!
__________________
500mw 405nm eBay labbie
1W 445nm built by yobresal
Uniphase-Cyonics 2201-25ML 488nm+ Argon
Sanwu 304 80mW 532nm
Gammax 1A415 1mW 632.8nm HeNe
LPC-826 250mW 658nm labbie (waiting for heat sink and driver)

11-04-2016, 11:05 PM #27
 Class 4 Laser Join Date: Sep 2007 Location: Wisconsin Posts: 9,315 Rep Power: 385035
Cyparagon
Class 4 Laser

Join Date: Sep 2007
Location: Wisconsin
Posts: 9,315
Rep Power: 385035
Re: Is an unfocused 4W laser do dangerous at 5 meters?

ALL the light being the difference here. No one makes a flashlight or laser and throws 99% of the light away. If you take a minuscule portion of the light, you can get better results. The final intensity is still proportional to emitter size, and the intensities involved in lasers and moonlight aren't really in the same ballpark, are they?
__________________
A problem well stated is a problem half solved.

11-06-2016, 02:31 AM #28
 Class 2 Laser Join Date: Nov 2009 Location: Shelby Township, MI Posts: 331 Rep Power: 51
Drivinfast247
Class 2 Laser

Join Date: Nov 2009
Location: Shelby Township, MI
Posts: 331
Rep Power: 51
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by bluestars If the FDA calls 5mW safe for direct exposure, and this is equivilent to 4mW, wouldn't that mean the FDA would call this situation safe? I'm also curious - what makes bright flashlights safe but (unfocused) laser diodes dangerous? Assume a 1000 lumen flashlight with a 15 degree spot, 75% of power in the spot, and 250lm = 1W output power. At a distance of 1m, the light would have spread to a circle of radius 100cm * tan(7.5degrees) = ~13cm. (75% of 1000lm) / (250lm/W) = 3W light power. 3000mW / (pi*(13cm)^2) = 5.65mW/cm² That's about half as much as the calculation for the OP's situation, but still in the same order of magnitude. You can easily buy a 3800lm flashlight for around \$50. How is this not dangerous? Admittedly, the power density of a collimated and focused laser, even something with only a few hundred mW, is much much higher than either situation given in this thread, which is where the severe danger of lasers can be found. Edit: Just to add, empirically and anecdotally, I have pointed my 1W 445nm laser at the wall without its lens (so unfocused). From a meter or two away from a white wall, the beam is not particularly painful to view. It certainly isn't as bright as the reflected spot from my 2500lm triple Nichia 219C flashlight, which leaves a faint afterimage when I look away. Leaving aside blue light effects, which is more irresponsible with my vision - looking into the beam of a ~3000lm flashlight or looking into the (unfocused) output of a laser?
Where is this \$50 3800lm flashlight?

11-07-2016, 01:08 AM #29
 Member Join Date: Jun 2010 Location: SF Bay Area, California, USA Posts: 41 Rep Power: 0
bluestars
Member

Join Date: Jun 2010
Location: SF Bay Area, California, USA
Posts: 41
Rep Power: 0
Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
 Originally Posted by Drivinfast247 Where is this \$50 3800lm flashlight?
The Convoy L6:
https://www.fasttech.com/products/1653/10002364/5184101
__________________
500mw 405nm eBay labbie
1W 445nm built by yobresal
Uniphase-Cyonics 2201-25ML 488nm+ Argon
Sanwu 304 80mW 532nm
Gammax 1A415 1mW 632.8nm HeNe
LPC-826 250mW 658nm labbie (waiting for heat sink and driver)

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

All times are GMT. The time now is 06:35 AM.

 -- DarkShadows V5 -- Responsive LPF -2562016 -- Default Style Contact Us - Laser Pointers - Archive - Top