Fresnel lens - what is it, testing focal length, solar heat generated
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- เผยแพร่เมื่อ 1 ส.ค. 2024
- Things I learned about fresnel lenses when I made my solar cooker. What is a fresnel lens? Should the grooved side face the sun or the flat side? Is the focal length the same i.e. same focal point? Is the heat output the same? Why do I get the results I do? What is spherical aberration? What are different types of fresnel lenses?
The large fresnel lens came from a rear projection TV. The smaller fresnel lens is a magnifying glass.
To see the TV is came from, watch "Fresnel lens solar cooker using TV lens":
• Fresnel lens solar coo...
See also "Fresnel lens and mirror solar cooker cast iron pan" where I combine this with a mirror for solar cooking:
• Fresnel lens and mirro...
For more see:
rimstar.org/renewnrg/solar_coo...
An excellent document about fresnel lenses that confirms my test results:
www.fresneltech.com/pdf/Fresne...
- rimstar.org - วิทยาศาสตร์และเทคโนโลยี
Wow, great informative video. Great information, and no unnecessary info.
Our local lighthouse has a fresnel lens, and now I know how it works. Thanks!
I just removed one of these Lens from a TV that was put out on the curb. This info will help me alot with my set up. Now If I can just figure out how I want to build my stand. Can't wait to try it out!! THX US Army Retired Iraq Vet
Cool! From experience I recommend going with a sturdier stand than mine, probably wood or metal. I went the way I did for extreme portability and storability. Have fun!
Re spot or linear being better, it depends on what you're using it/them for. The amount of energy in the line is the same amount of energy in the spot, just concentrated differently. For example, if you're heating up the bottom of a frying pan and you can get all the line or all the spot on the bottom of the pan then it doesn't matter which. However, with a spot, you can pull back and cover the whole of the round pan more evenly. Of course if it's a rectangular pan, ...
I'm addicted to the forum now, thanks!!!!
It's no problem at all. Thanks for showing it to your website visitors. Greetings from Canada.
I haven't really experimented with 12x8 inch lenses for melting or burning things. They can burn paper, leaves, ... but you have to keep them focused at a spot for a little time to build up the heat. A cup of water would take forever and would probably never get to boiling simply because the heat loss would be as fast as the heat gain.
You're welcome, John. I'm glad to see my videos being of some use. -Steve
You're very welcome! I hope you find it useful.
Neat idea. I'll add it to my todo list. Thanks!
Thank you very much, looks like I got an even mix of both, fortunate! They are clear and very powerful so far.
I can feel the grooves on one side but the other side feels smooth. When I run my fingers lightly over the grooved side it even makes a sound (can't really describe it) but the smooth side makes no sound. Mine is far from transparent, so my grooves are probably wider apart, but I have a magnifying glass one that is more clear and I can feel and hear the grooves with that one too.
Rimstar your information was very helpful. I had the outer cover on the out side of my lens and that was a no no.. When I took it off I got it to burn.. Now for my pool heater project.. Thanks for your Video.
Good info. Thorough investigation. Thx.
Thank you very much! For both the information, and the time I know you must have put into this! ~Kevin~
It is important to know which side the lens to be used.
Most people ignore them or purposely use flat side to the sun b/c the dust from the air.
@astrobreaux I don't have a spot fresnel to test with but from my reading, it should have the same sort of difference when flipped. The difference doesn't have to do with whether it's spot lens or linear lens. I'll put a link to the document in the video description.
Keep making these great videos! Doing the experiments so we don't have to
You're right in that it isn't perfectly flat and having a flatter one would probably make some difference. But the difference I got between grooved side facing the sun and facing away from the sun was too large I think for that to account for it. Also, the spherical aberration I mentioned is a very real thing, not a guess.
Good science! This is helpful to know which side facing the sun provides the most power. And just think... if you had not found that old TV with the free parts, you might not have ever bothered to test this.
sir can you please make a video on the spectrum of light and rainbows...they interest me a lot and i have a lot of doubts in it....
Thanks! Just got 6 (!) Fresnel lenses, wanted to get more knowledge of such, appreciate your video! Is the spot or liner better?
@field16 I was thinking the same thing, pure luck that I found it. It does help to keep an open mind. Of course if I hadn't I would just have gotten into some other mischief. :)
Unfortunately I'm away right now and won't be back until next week to check. But for my small magnifying lens fresnel lens the adjacent rings are touching. I guess the other question would be how many rings are there per inch. But again, I don't have access to it right now.
I don't know what type or what material. I took it from a discarded rear projection TV I found beside a road here in town. See my video "Fresnel lens solar cooker using TV lens" to see the TV. There's a link to it in the below this video and on my channel page.
does the spot focused fresnel lens have the same heat output difference as the linear focused when flipped? thanks for the info on the output differences, which will come in handy for cooking some things at a lower temperature.
Good job, Thank you very much
Sorry, I didn't mean to sound confrontational, which I think my last part did. My apologies. I don't think firming up the frame would make much difference to this experiment but I did fail to heat up sand enough in a separate experiment to form glass where a small, hottest as possible spot was needed. Now that you mention it, a better focal point from a solid frame would have helped there.
Awesome video! Could we make two grooved sides on same fresnel lens to enhance the magnify effect ??
It's already focusing all the sunlight that arrives at the lens to a point (except for losses due to reflection and absorption). Adding more groove won't add more sunlight.
Use a more rigid and stable frame, you are getting a "blurred" focal length because the lens is bowing under its own weight, you want the lens as straight and perpendicular to the sun as possible
2:16 on the video shows that grooved angles help reduced inside grooves looked curved
Ah, in your comment on my other video I thought you were talking about the whole rectangular len being curved. My misunderstanding.
Sent over from David West channel
What is the distance between the concentric circles cut into a spot Fresnel lens?
What position did you leave the lens in relation to the azimuth angle of the sun?
The lens was facing the sun directly, so the difference between the azimuth angle of the sun and the azimuth angle of the lens was zero. At 2:42 in the video I show my sun finder that's taped to the side of the lens and I point out that it's facing the sun.
what type of fresnel lens did you use? was it polarized, IR? what material was the lens you used made of?
Ouch. That would be a lot of concentrated sunlight. Did you try melting anything with it?
What could a 12x8 inch fresnel spot lens do? What could it melt etc.?
Never said it was a guess. I'm just saying you might be able to get more clarity on your focal spot if you solidify your frame, that was all. just trying to help.
Infrared isn't heat. That's just a common misconception. Infrared and visible light are both different sets of electromagnetic waves, hence the camera with settings for both. Infrared waves have longer wavelengths and visible waves have shorter. When they're absorbed by materials, they may be converted to heat, depends on the material. With visible wavelengths the material's color determines what gets converted to heat. Black is best. I don't know what materials convert infrared wave to heat.
You translation said "course" but I think you meant "graph" or "chart". No, I didn't make a graph of rising temperatures.
Hi, would like to find out how long it would take to boil the water, also how is it that a guy in Hawaai can melt copper with a fresnel lens but your lens seems to be okayish? What is the max temp output of a fresnel lens?
Jason Sole The water boiling time depends on how much water, what the outside temperature is, how good your lens is and how strong the sun is. So hard to say. On a summer's day I've boiled around 500ml of water in around 20 minutes, but I'm in Ottawa so the sun isn't as strong as Hawaii and my lens isn't the best. I think it's the more lines in your lens per area, the better the lens.As for the max temp output, or really the max energy output, depending on where you are located the sun gives around 1000 watts per square meter or less. According to charts, here in Ottawa in June we get around 700 watts per square meter in June. Then that light has to go through your lens and so there are losses, and the amount of loss depends again on your lens. I don't know what the amount of loss, or efficiency, of a fresnel lens is.
Making it a spot lens?
If you polished the ungrooved side would it be hotter.
Actually infrared isn't heat. That's a common misconception since heat from objects around room temperature emits electromagnetic waves at infrared wavelengths.
But I never thought about the different focal length issue. Different frequencies refract at different angles. I never thought that through, thanks. Though that's true even for the visible frequencies. Of the 1kW of energy around 50% is visible and 50% is infrared. I wonder if focusing infrared could be done with night vision goggles!
yes i thik graph,,Thanks for answer
that might be classified Sir ... ☻
but im definitely a subscibed fan ☺
hi I need big size 2fit × 3fit fresnel lens is available were I can get this... please send link of it.... thanks for share...
You can buy them here greenpowerscience.com/SHOPFRESNELHOME.html
If one of these lenses could be made to have a long oval focal point, and a concentrated temp of 165 F it would make amazing stale carrot beds with no propane!
so in solar cooker Fresnel lens are used?
Mrunal Ahirrao Some solar cookers use a Fresnel lens, like this one th-cam.com/video/eg4IKB3Es-A/w-d-xo.html . But in many solar cookers reflectors (mirror-like surfaces) are used instead, such as in this other solar cooker of mine th-cam.com/video/Gjr-VHq12kk/w-d-xo.html
How can I make one like this?
אור ברוך I found the fresnel lens in an old rear projection TV. You can see my video about it here th-cam.com/video/wprlzCDfLm8/w-d-xo.html.
would you like me to manufacture these lenses for you? btw, I make them 4ft.x3ft. and they are not frosted …making them hotter that TV lenses
+Sci Ense how much is one man? can u send me a mail to a.nikhil.an@gmail.com
i am frm india chennai. need it for a project in college
What? No!!! My videos should be encouraging you to get your hands dirty! Otherwise I've failed. :(
:D
Seriously. Thanks for the encouragement. I'll keep at.
yes i think graph,, because i need graph for school.
thank for answer :)
:)
imagine 5 , all going to there own Mirror (kinda) ...
then all the mirrors , direct the beams to one point ... or aiming mirror ..
yeah ... i had to take it apart before somebody thought i was a terrorist or some shit ... which im not lol ☻
You know you can transform your foggy linear lens into a clear spot lens, which is much more powerful ;)
TTime685 How?
RimstarOrg Simply fill in the linear grooves on the opposite side from the Fresnel rings. All you need is a can of Minwax (brand) polyurethane or polycrylic and make sure its the clear/crystal-clear type. You can find it at walmart. Just use a paint brush to apply one or two coats, possibly three depending on how deep your groves are. Some lenses have deeper grooves than others. Doing this also makes the lens more clear which is necessary for acquiring even more power. It might not turn out to be super crystal-clear but it'll definitely be clearer than before. Remember.. don't touch the Fresnel side.. only apply to the linear side. Let me know how it goes!
TTime685
There are no linear grooves on the non-Fresnel side. One side has the Fresnel grooves and the other side is smooth. I verified it both by touch and by looking through a magnifying glass.
RimstarOrg Ah ok. I just noticed in the video that you said your focal point is about 3 inches long. From what I've experienced lenses without the linear grooves (that are smooth on the non Fresnel side) create a point focus, not a linear. Also, your lens seems to be from a 16:9 ratio HD Tv which are the worst for solar applications. They work ok for cooking food and boiling small amounts of water, that's about it. I haven't had much experience with 16:9 ratios but the one I did have was smooth on one side, foggy, and it focused to a point, not a line. That's why I though yours had linear grooves. It was ok for cooking and boiling water but I gave it away and upgraded to bigger and better. 16:9's tend to be foggier or more frosted than 4:3 ratio TVs. Obviously the more clear the lens is the better. On some linear lenses the fine grooves make them foggy only until you fill them in and then it becomes a more clear spot lens. The smooth and foggy 16:9 lenses can't be helped.. so I guess that's what you have. Sorry if I got your hopes up :-/ But good luck on lens hunting!
TTime685
Just to be sure, I think you meant my focal point is about 30 inches. 3 inches would be pretty short.