Is Time Really A Factor?

justinjja said:

fair enough,
if i recal correctly most high power IR laser diodes have a fairly signicant fast axiz,
meaning you will get a square or line like output from the laser.
so it will still be hard to get an even circle of light

but other members will know more about this than me

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But this doesn't signify that the Intensity will be equal across that "square" right?

Not at all. As was just stated, multimode diodes exhibit hot spots by their nature. The expanded beam will have very uneven power distribution.

.......

justinjja said:

I'm fairly confident this is not correct: "A 1-second exposure of a 1mW source is the equivalent of a 1/1000s exposure of a 1W source"

I would much rather stare at a 1mW laser for 1 sec, that have a 1W flash in my eye for a ms.
For one you would blink if a 1mW laser was shinned in your eye for 1 sec,
and two i believe that over the time of 1 sec, the heat being aplied to your eye could be dispersed to some extent.

However he is is probably correct is saying you will have hot spots in your ring, 445 diodes just dont put out a nice round dot

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Where would the heat be dispersed into?

Your body?
I'm not saying time isn't a factor, it sure is
But rather that it is not a linear relation like he described
Can you light a match by shining a 1mw laser at it for 1000 seconds or
Can you burn ur hand with a 1 mw laser? Probably not
But 1sec with a 1 w laser, you bet

Edit:
Something worth noting about that post, I was under the impression the op was talking about a 445 laser.
You do not have a blink reflex to IR light, making it even more dangerous.

Time is always a factor with ANY kind of radiation exposure, no matter what the type or source. Whether or not injury is involved depends on the type, power level etc. but the longer an object is exposed to radiation, the more the object absorbs or otherwise interacts with the radiation.

EDIT: Just read part of the previous post that I missed. The amount of energy absorbed by a given material exposed to (for example) 1mW over 1000 seconds and 1W over 1 second is the same. It's because of the time it takes for the energy to be absorbed that is the reason for the difference in effect and this is dependent on the nature of the substance absorbing the radiation and the nature of the radiation itself. A substance or material will be able to cope with the heating effects of 1mW sustained over 1000 seconds because any heating of particles then transfers to adjacent particles and so on, dispersing the heat over a comparatively large area. When the same material is hit with 1W sustained for 1 sec. the heating occurs much more rapidly and the particles in the substance have less time to transfer the heat to adjacent particles so instead the particles directly exposed to the radiation are damaged, altered or destroyed. The localized nature of such sudden heating results in much more damage to the material.

justinjja said:

I'm fairly confident this is not correct: "A 1-second exposure of a 1mW source is the equivalent of a 1/1000s exposure of a 1W source"

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Yeah, that's not right. You are exposed to several microwatts of light from being outside in the daytime. So by that logic, An exposure time of ~1000 seconds of being outside is the same as getting hit with a 1W laser for 1ms.

BrittanyGulden said:

...I am looking to illuminate an area of several hundred yards W/ a width span of several hundred yards.

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For a 1:1 ratio like that, the divergence needs to be 60 degrees. That is well within the capabilities of an LED array. Lasers are great for many applications. General illumination is not one of them.

Cyparagon said:

Yeah, that's not right. You are exposed to several microwatts of light from being outside in the daytime. So by that logic, An exposure time of ~1000 seconds of being outside is the same as getting hit with a 1W laser for 1ms.

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In terms of the cumulative energy absorbed the two would be the same. I think that might be where some confusion lies..

I think the reason they want to use a laser is they want to illuminate a swath of land from a distance with next to no lighting effects between the source and the target areas and low loss of energy density between the source and target.

I.e. from 100yds away they want to illuminate an area of 100sqyds

First note: power and energy are different. This is the point that is confusing people, they just don't know it.

Second note: You have already tried LEDs. They worked fine for near field. Add an aspheric lens and they ought to work fine for far field.

They are different, but related. Stating power is basically stating how much energy is present over a given time period. If more energy is present during a shorter time period you have more power.

I think it's classified on the United States' Abrams MBT, but I know the Russians have been using IR spotlights for general night illumination, giving the sinister "stalking red eyes" look to the most recent T-90 MBT. Those spotlights would be great for your purpose, I know being a tank outfitted with a 125mm smooth bore it needs at least a few hundred meters of daylight, even in total darkness.

This seems to be a toned down version, for IR illumination with the new IRNV gun sights; http://www.amazon.com/gp/product/B0..._m=ATVPDKIKX0DER&pf_rd_r=1J96F289E2AS424RWS2F

^ Ah, but that takes the fun out of DIY

This will give you a very good idea of what I want to do. Of course, I will be using a more Powerful laser Diode in hopes to "beam out (illuminate)" at greater distances W/ a greater Width span.

LucidScience - Build the LASER NIGHT VISION - Page 1 of 13

^ used a Scope as a "Zoom." I will be excluding the use of a Scope & finding a Digital Camera W/ a very good optical Zoom.

I just didn't know exactly how to go about "dispersing" the "beam" so I could illuminate an area. Maybe it'd be easier to just buy a Laser pointer, but I only assume it's not going to have the focus I want. I need a pretty wide one....

I'd try using two or more singlemode diodes to get more power, completely without any form of lens, see what that gives you. The only thing I might worry about is power levels where the cones of light overlap, but at singlemode power levels the raw, highly divergent beam shouldn't pose any hazard except within 1.5cm or so of the source. You'll get more even power distribution going this route.

I'd rather sit and have a light bulb irradiate my hand for ten hours than have an acetylene torch flame on my hand for ten seconds. The former would do nothing, the latter would leave me with horrific burns.

The cumulative energy could be nearly the same, but my hand can only dissipate but so much energy in a given amount of time.

Trevor

IR lasers are more dangerous than visible lasers because you can cause damage without realizing it. It is very true that the more you disperse the beam the less dangerous it is. Different people have different ideas as to what power it actually becomes dangerous.

When you are working with 5mw or less the only danger is if you somehow stare into the laser for an extended period of time. With visible lasers this is nearly impossible to do, but with IR lasers it wouldn't be hard. Especially if you leave your laser on by accident. I highly suggest you use some mechanism that makes it impossible to accidentally leave your laser on.