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Old 10-21-2016, 04:10 PM #1
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Default Is an unfocused 4W laser do dangerous at 5 meters?

I will buy a 4w laser, I want to know if the laser will be unfocused and have a spread of around 20cmx20cm(8"x8") at a distance of 5 meters.

Will it be dangerous if it will hit the eyes?


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Old 10-21-2016, 04:15 PM #2
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
Originally Posted by dreamsfain View Post
I will buy a 4w laser, I want to know if the laser will be unfocused and have a spread of around 20cmx20cm(8"x8") at a distance of 5 meters.

Will it be dangerous if it will hit the eyes?

You already have a thread asking the same question. Please avoid creating multiple threads for the same thing.


But yes, that is dangerous. If you need to ask then you're not in a position to do that sort of thing safely.
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Last edited by diachi; 10-21-2016 at 04:18 PM.
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Old 10-21-2016, 04:18 PM #3
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Ok that was in the new comer section, my bad
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Old 10-21-2016, 06:03 PM #4
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Besides, different diodes have different spreads or angle outputs in degrees, you would need to be more specific regarding the diode you are wanting to use but if you started another thread on this either continue with that one by linking to it now and let this one go silent, or vice versa. I would PM you but I changed my settings to only allow previous contacts to PM me.

Laser diodes are great for focusing down to a tight spot for maximum energy on a tiny target, or for producing coherent light, why in the world would you want to use an expensive laser diode that way; with the light spreading out quickly neither focused to a spot or made into a tight beam focused to infinity? Maybe you would be better off using an LED, or LED array.
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Old 10-21-2016, 10:02 PM #5
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Assuming a tophat intensity profile, 4w/(20cm*20cm) = 10mW/cm². This is above MPE, but would be roughly equivalent getting a direct hit from a 4mW laser, as maximum pupil diameter is ~7mm, or .38cm².

tl;dr: not safe.
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Old 10-21-2016, 10:13 PM #6
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
Originally Posted by Cyparagon View Post
Assuming a tophat intensity profile, 4w/(20cm*20cm) = 10mW/cm². This is above MPE, but would be roughly equivalent getting a direct hit from a 4mW laser, as maximum pupil diameter is ~7mm, or .38cm².

tl;dr: not safe.

Why do I always think it's 11mm? My calculations (as in the process itself and all other numbers) were correct (didn't post them) but that doesn't do much good if one of the numbers you used is incorrect... Thanks for posting the math!
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Last edited by diachi; 10-21-2016 at 10:14 PM.
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Old 10-22-2016, 07:05 AM #7
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Good model, but how close does the particular diode he is intending to use come to it? Perhaps worse, I can't imagine the application but am curious to know.
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Old 10-22-2016, 10:30 PM #8
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
Originally Posted by dreamsfain View Post
I will buy a 4w laser, I want to know if the laser will be unfocused and have a spread of around 20cmx20cm(8"x8") at a distance of 5 meters.

Will it be dangerous if it will hit the eyes?
YES IT WILL BE DANGEROUS!

Remember the center of the output unfocused or not can be more intense, if you are thinking about a dazzler they are a bad idea, a bright flashlight, especially with strobe mode and pepper spray is a better choice.




I was thinking about getting a bigger driver for my sky ray king with 7 x XML-T6 and found this one that's programmable.
Funny thing I noticed about mine is the strobe is faster than most, maybe around that 13 pulses per second because when I hold the switch down if jumps into strobe and in about 2 seconds my stomach starts feeling sick.
I have never felt this effect before but it happens every time and persists for minutes after I turn it off.
There's something to that "sick light" effect, I am guessing at 13 per second as that's an epileptic trigger I have heard, I have never felt any epileptic symptoms, but this one does mess with my stomach oddly enough.

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Old 10-23-2016, 02:34 PM #9
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

What are your hidden talents? What is something you feel you are extraordinary at, but is such a useless skill that you would never actually brag about it?
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Old 10-30-2016, 07:39 AM #10
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
Originally Posted by Cyparagon View Post
Assuming a tophat intensity profile, 4w/(20cm*20cm) = 10mW/cm². This is above MPE, but would be roughly equivalent getting a direct hit from a 4mW laser, as maximum pupil diameter is ~7mm, or .38cm².

tl;dr: not safe.
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?
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Old 10-30-2016, 09:06 AM #11
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Great points, waiting for the answer.
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Old 10-31-2016, 06:42 AM #12
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

I realized all of this calculation could be simplified if I just got out the laser and flashlight and directly compared.

In one corner, we have a 1000lm Convoy C8 with a Cree XP-L Hi LED. In the other corner, we have a 1W 445nm laser built by yobresal with the focusing lens assembly removed.

The edge of my desk is almost exactly 3 feet away from my white bedroom wall. Here's what I saw with the 445nm laser:
https://i.imgur.com/jdBYwkm.jpg

Here's what I saw with the Convoy C8:
https://i.imgur.com/IT03Jqd.jpg

Here are both active at the same time:
https://i.imgur.com/F1wx9kl.jpg

I used my girlfriend's NIKON D3300 in manual mode, 1/1000 sec exposure with F 1/5.6" at ISO 800, and didn't change settings between those three shots. I'd say in person that the reflected white light from the flashlight is comparatively more intense than the images show.

Both produced a 42-inch diameter "spill" (fast axis for the laser). The laser "spot" was 10 by 42 inches, and the C8's spot was 3.5" in diameter. I'd say ~70% of the power went into the spot of the C8, but I have no good way to measure that. Just from the photographs, it seems to me that the laser produced a significantly lower intensity at the wall than the flashlight did. Scale the intensity of both of them up by 4x and you get roughly the situation I was describing above: 4W laser vs Convoy L6 (3800lm) flashlight at 1m. At this point, I'd have to say that I'd rather take an (UNFOCUSED!!) 4W laser hit than a hit from a L6 at such a close range.

But that's a bit like asking which caliber you'd rather be shot with, a 22 or a 45. I'll stand over here where nobody is pointing flashlights or lasers or guns at me, and you can go somewhere else and do that nonsense!

Here are a few bonus images and beam shots:
https://imgur.com/a/ITucC
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Old 10-31-2016, 08:12 AM #13
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

If I were home I would try this same thing with a laser power meter, that would give some good info too.
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Old 11-01-2016, 01:17 AM #14
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
Originally Posted by bluestars View Post
If the FDA calls 5mW safe for direct exposure...
5mW is not safe to point in the eye. Please read the safety article before commenting further.

Quote:
Originally Posted by bluestars View Post
I'm also curious - what makes bright flashlights safe but (unfocused) laser diodes dangerous?
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.

You can simulate the eye's lens with a magnifying glass. Focus a laser with it, things burn. Focus a flashlight with it... not so much.
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Old 11-01-2016, 11:17 AM #15
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

That makes sense, as a point of interest, the sun is so far away the rays are essentially parallel too, but a flashlight, not so much. However, I wonder at what level a flashlight has enough power to produce the same amount of power density a 5mw laser can produce within a given area, even if the flashlight has a much larger area due to being unable to focus to as small a spot?
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Old 11-01-2016, 03:13 PM #16
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Default Re: Is an unfocused 4W laser do dangerous at 5 meters?

Quote:
Originally Posted by bluestars View Post
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?


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?

That 5mW figure assumes the blink reflex protects you from damage. 5mW still has the potential to do damage with longer exposures.

Cyparagon already answered the laser vs flashlight question so I won't repeat his explanation.
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