LPM Testing with various sources.

[Isoleucine]

As a kid, most of us have enjoyed using a magnifying glass to ignite things on fire. Some LPF members have picked up on this and have been brought into the laser hobby like most people (like me, haha). Considering the brightness of the sun, and its concentrated power with a magnifying glass, how many mW is the lighted spot?

I think its roughly 30-40 mw for looking at the sun, but it could be a totally different value considering it's brightness. Probably higher. Concentrated, the focused beam of light could be higher than 1W of power.

This may sound like an absurd experiment, since using a magnifying glass is kid stuff... but considering the power of the lasers here, which ranges from 5mW to over 100W, this may be a considerable experiment to try out.

Since I do not have a laser power meter, performing this experiment is a no-go for me. However, doing this experiment could give a reference to new members in seeing how powerful hobby-based lasers are. I've heard many videos, threads and posts strongly suggesting NOT to look at the beam dots, or into the beam or even at the beam. Yes I can agree that, but as a scientist, I would also like to personally know.

Allowing newer people to compare the brightness of a focused sun ray and it's power to a Class 4 laser could give insight to people.

:beer: -Iso

 

[lasersbee]

As a kid, most of us have enjoyed using a magnifying glass to ignite things on fire. Some LPF members have picked up on this and have been brought into the laser hobby like most people (like me, haha). Considering the brightness of the sun, and its concentrated power with a magnifying glass, how many mW is the lighted spot?

I think its roughly 30-40 mw for looking at the sun, but it could be a totally different value considering it's brightness. Probably higher. Concentrated, the focused beam of light could be higher than 1W of power.

This may sound like an absurd experiment, since using a magnifying glass is kid stuff... but considering the power of the lasers here, which ranges from 5mW to over 100W, this may be a considerable experiment to try out.

Since I do not have a laser power meter, performing this experiment is a no-go for me. However, doing this experiment could give a reference to new members in seeing how powerful hobby-based lasers are. I've heard many videos, threads and posts strongly suggesting NOT to look at the beam dots, or into the beam or even at the beam. Yes I can agree that, but as a scientist, I would also like to personally know.

Allowing newer people to compare the brightness of a focused sun ray and it's power to a Class 4 laser could give insight to people.

-Iso

I have done the Noon Summers Day Sun's power test.
On an 8mm X 8mm square axtive sensor area. We got
a reading of ~52mW of sunlight.
That makes perfect sense since the atmosphere absorbs
a bit of the sunlight that reaches the earth.

These may explain your idea a bit...

http://laserpointerforums.com/f54/sun-magnifying-glass-mw-38730.html#post422379

Sun's Power Idea



Jerry

 

[RayBurne]

Edit: 20110704: I reran my calcs and the below math is wrong as Jerry indicates in the next post. Correct calculation is: 1000W / 1550 in2 * 12.5 in2 = 8.065W for the 4" magnifying glass... Boys and girls- watch those oughts 'n naughts! I left the original wording below to show that I made a mistake but substitute 8.1W when you see 8.1mW. Peer review is great!

Ol' Sol provides roughly 1KW of energy per square meter (1550 Sq. In.) at ground level. When this is "concentrated" by a magnifying glass, we decrease the area over which the energy is absorbed - the spot size is diminished; the smaller the spot size, the smaller the area relative to the original 1 square meter. A 4" diameter magnifying lens is about 12.5 sq. in. or 0.0081 sq. meter. So the 4" magnifying glass starts out with 0.0081 x 1KW or 8.1mW of energy and the smaller we can make the dot, the more we concentrate that 8.1mW and the higher the temperature created at the focal point. BUT - no matter how small that dot becomes, we never have more than 8.1mW of energy total.

Concentrating the sun's energy is awesome. Check out: Dr. Simons' experiment
Giant Fresnel Lens Deathray: An Experiment in Optics
... this gets pretty interesting around step 4.

More crazy experiments and destruction can be found on You Tube, just search "Fresnel"...

Concentrated solar energy is dangerous and experiments by children should be supervised by responsible adults (if any can be found in the forum, present company included!) :crackup:

Burn on!

- Ray

 

[lasersbee]

There seems to be something amiss in your calcs....:thinking:

A 4" diameter lens or 101.6mm diameter lens has
a surface area of ~8107mm2

Under Ideal conditions at noon... in the middle of the
summer with absolutely clear sky and air and at 90 deg
to the Sun's rays there is ~1000 Watts of the sun's heat
energy hitting every square meter on the earth's surface...

That is 1000mm X 1000mm = 1,000,000 mm2
1000Watts/Meter is 1000W X 1000mW = 1,000,000 mW
Therefore there is ~1mW/1mm2 of energy from the sun...

In the experiment I did last year I got a reading of ~52mW on
a sensor with an active surface of 64mm2 (8mm X 8mm).

It was around 1:00PM at the end of August IIRC and the air
was probably not 100% clear...

With a 4" lens you would be collecting 8107mm2 X 1mW = 8.1Watts
of energy not 8.1mW....

Unless I've made a mistake....:undecided:


Jerry

 

[Isoleucine]

I think I approve, since the magnifying glass is a very powerful tool. The beam dot can stun the eye visually, so I approve of your readings/idea. +1

thumbs up!

 

[RayBurne]

GeeWhiz, Jerry, I screwed-up! I really should have used my old HP67 from college instead of that $1 battery-solar dual power calculator that hangs around the workbench and is most often used as a four-banger!

I'm so shamed... :yabbem: So much for "so easy a caveman can do it..."

 

[Benm]

You can collect a lot of power with a magnifying glass indeed. The 8 watts from a 4" lens sound about right to me. The 1 kW/m2 is a bit optimistic though, you may get it around noon in summer on a clear day if you live in southern europe or the southern states of the US.

I have a 20x30 cm fresnell lens here that will light a bbq at 6 in the afternoon under the dutch summer sun. Under ideal conditions it would catch 60 watts of light at noon, but i suppose you don't need that much to start a fire

 

[lasersbee]

GeeWhiz, Jerry, I screwed-up! I really should have used my old HP67 from college instead of that $1 battery-solar dual power calculator that hangs around the workbench and is most often used as a four-banger!

I'm so shamed... :yabbem: So much for "so easy a caveman can do it..."

:crackup::crackup::crackup:.... No Problem...

I used an abacus....and a pointy stick...


Jerry