The forum discussion centers on the optical phenomena observed in reflections from double glazed windows, specifically the appearance of a cross shape and circular patterns on an opposite wall. Participants explain that the cross may result from the curvature and surface variations of the glass, while the circular reflection is attributed to the sun's rays. Key factors include the angle of sunlight, the distance between the window and wall, and the properties of the glass, such as its potential concavity and the presence of coatings. The discussion highlights the complexity of light behavior in relation to double glazing and encourages further exploration of optical principles.
PREREQUISITESAnyone interested in optics, architects, builders, and homeowners looking to understand the visual effects of double glazed windows and their implications for design and energy efficiency.
I think you need to provide a detailed diagram of the arrangement if you want a credible explanation. You seem to be assuming that the pattern actually appears on the wall but I don't think you would see that pattern on the wall if you went outside. That would have to involve some sort of projection arrangement (curved mirror or lens). So far, it looks to me as if it's a virtual image but you could solve this by moving your head from side to side and seeing if the cross appears to move over the wall.brbrown said:
I think this requires some explanation from you. What light path(s) are you using for this effect?Keith_McClary said:
russ_watters said:
One possible reason that you have had such a variety of answers is probably that you really haven't given us a good idea of the actual setup. It's obvious to you, 'cos you were there but some important details are missing for us. When you were actually outside, looking directly at the wall (not through the window) did the pattern look any different from the view from indoors?? Was the sun low or high in the sky (perhaps just peeping over the wall at the window? How far from the wall was the window? Was the light path from the Sun obstructed in any way. Was the sky actually clear?brbrown said:
I'm really confused what you could have meant by this. The Sun radiates in all directions, of course, so what would the "extent" mean?brbrown said:
Keith_McClary said:
That's true but the size of that rectangle would be a rectangle that's larger than the window. Same as if the Sun were shining through a doorway; a larger image of the doorway would appear on the opposite wall. The same rules apply as for shadows - always an image bigger than the obstruction and not 'focussed' any way.Keith_McClary said:
This, also doesn't make sense in this context. Whilst it's true than a convex lens or concave reflector can produce a real projected image, the distance of the wall from the window and / or the probable curvature (giving a focal length) makes this unlikely - UNLESS, and I have made this point twice already, the reflecting window is a long distance from the wall but this information has not been given yet so we can only speculate.Pratyeka said:
That shows the same effect as in the OP. "Sunlight Reflected from Double-Paned Low-E Windows, and Damage to Vinyl Siding and Other Materials"Pratyeka said:
You have not remembered your elementary optics quite correctly. There is no equivalence between the pinhole and a large flat reflector images. If you had taken your shoebox and made two pinholes in it, the image would have been two Suns. n pinholes produce n Suns, side by side and a large square hole An infinite number of pinholes produces an image that's square and of a similar shape as the hole and larger, according to the ratios of hole size, projection throw etc. ). Without some curvature, you can get no real image formed. Why would anyone use a lens if a big hole would do the same job?Pratyeka said:
That's a good image, repeating the effect in the OP. I can't think there's any doubt that it's a focusing effect of a curved reflector. Although they still don't mention the actual distance between window and wall we now know we're talking in terms of across a street (say 50m). That must be similar to the curvature of one of the glass faces (it could be either) to form that basic part -focused spot. Pressure differences due to heating of the units on a hot day could make the bowing worse. The actual shape of the glass wouldn't be spherical, the curvature would be different along the diagonals and for the verticals and horizontals. That's astigmatism, which produces that sort of distortion.Pratyeka said:
. You have all given me a lot of interesting comments and I thank you all for your help, interest and perseverance.Atmospheric pressure is 10 tonnes per square meter.Blue Chuzzle said:
Orthoceras said:
I have a crank-out window like that, so I can (hypothetically
) adjust the beam to zap passers by.You wouldn't get a focused image either - just a massive bright disc with penumbra.marcusl said:
Vacuum Insulated Glass is not yet widely used. The spacers, on a 20 mm grid can be made from stainless steel or glass, with a thickness of 0.2 mm and diameter 0.6 mm.sophiecentaur said:
Good for some things but flare could be a real problem for a picture window at the sunny side of a house.Baluncore said:
