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# Distance Experiments

#### Gsquared18

##### New member
Huh, are you asking seriously ?

MILLIwatt = 1/1000 of watt = 1000 milliwatt for a watt.

1.000.000 is for microwatt
Yeah, yeah I knew that, I was just testing you. You passed!!!

#### HIMNL9

##### New member
Yeah, yeah I knew that, I was just testing you. You passed!!!
LOL

Then let me test you ..... what is more high, 100 femtowatt, or 10 eptawatt ?

j/k

#### Gsquared18

##### New member
LOL

Then let me test you ..... what is more high, 100 femtowatt, or 10 eptawatt ?

j/k

Easy! Without question, 10 Petawatt. 1 Petawatt = (10^30) Femtowatts.

#### HIMNL9

##### New member
Wrong reply ..... cause the question was involving eptawatt, not petawatt

(no, it was not a typo ..... mega, giga, tera, penta, exa, epta ..... and so on )

LOL ! :crackup: :angel:

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#### Gsquared18

##### New member
Crap!! I copied and pasted your question into Yahoo Answers and some guy named Rajashekhar Shivaram Sharma provided that answer. With a name like that, I figured he had to be right.

#### RA_pierce

##### Well-known member
Attached are photos of >600mW pointed at some hills approximately 1.78miles away. These photos are pretty much as close as I could get to reality. Not the best camera. This laser is BRIGHT!
I have video, but my video camera is so old... it uses video cassettes.
I'll be doing some ~10 mile experiments when I have some time.
Edit: The last picture is a beam shot at about 5:30pm where I live. No exposure tricks. Yes... the beam IS fairly visible before dusk, with clear air!

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#### Gsquared18

##### New member
Attached are photos of >600mW pointed at some hills approximately 1.78miles away. These photos are pretty much as close as I could get to reality. Not the best camera. This laser is BRIGHT!
I have video, but my video camera is so old... it uses video cassettes.
I'll be doing some ~10 mile experiments when I have some time.
Edit: The last picture is a beam shot at about 5:30pm where I live. No exposure tricks. Yes... the beam IS fairly visible before dusk, with clear air!
Great pics RA thanks! Is that last one pointed at the moon or sun or is that the dot?

#### RA_pierce

##### Well-known member
Great pics RA thanks! Is that last one pointed at the moon or sun or is that the dot?
That is the moon.

#### RA_pierce

##### Well-known member
If you want to get an idea of how visible your laser will be at a given distance, you can do this easily. I'm no mathematician so forgive me if any calculation is flawed.

You can use this equation d= (b + Dm)/1000
You need to know:
Initial beam diameter in meters(b)
Divergence of laser beam (D)
And the distance you are measuring in meters (m)

For example, my PGL has an initial beam diameter of about 2mm, approximate divergence of 0.84mRad and I want to measure at 9.4 miles (15208 meters) (distance from my house to nearest mountain).
d=0.002+0.852(15208) = 12957.216/1000 = 12.957216m (42.5ft)
So at a distance of 9.4 miles the beam diameter of my PGL will be about 13meters across.

If you want to go a bit further, you can check this table for the Luminous efficacy at whatever wavelength laser you are using:
Luminous Efficacy
Both photopic (light adapted eyes) and scotopic (dark adapted eyes) conversions are listed.

To calculate approximately how many lumens your laser is outputting, take the lm/W value for your specific wavelength and multiply it by the power of your laser in Watts.
Again, for my PGL:
Photopic: 588.746 * 0.65W = 382.6849 lm
Scotopic: 1378.7 * 0.65W= 896.155 lm

I'm not sure how accurate this Watt to Lumen vs. Wavelength conversion is but it seems about right.

I hope this is useful info for somebody.

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#### mfo

##### Banned
That is the moon.
Enjoy the moon while you can because I am eventually going to set it on fire with a laser! Mwahahaha! :evil:

#### Gsquared18

##### New member
If you want to get an idea of how visible your laser will be at a given distance, you can do this easily. I'm no mathematician so forgive me if any calculation is flawed.

You can use this equation d= (b + Dm)/100

#### Lasher

##### New member
We have a place here in East Tennessee that is called Klingman's Dome. It is said you can see five states from being on top of it. What way to I need to point so you guys can look

Lasher

#### kevinmassey

##### New member
look at the description on the german video "These shows are done with a 8-16 Watt Lasers, that can easily cut trough arm-thick steel" haha i seriously doubt that

#### RA_pierce

##### Well-known member
HEHEHE the hulk 175mW vid is mine
I just got a 10X beam expander for my PGL. I'll be doing something similar soon.

I wonder what 650mW of green looks like at 10 miles?...