A WT? Moment

Don’t expect me to provide enlightenment. I’m lost.

So the garage door is unexceptional. Just a door to the garage Plywood, varnish. So tonight I’m loooking in the plate glass window to the back yard… In the reflection I see specular high lights of a yellow flash character along the hinge line of the back door. Lookig at it directly I see nothing other than the illumination of a 13 W CLF bulb in a lamp at about 45 degrees to the door.

So what causes the specular gold colored bright spots in the window reflection?

I have no clue and nothing I know of physics explains this.

Subscribe to feed

About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
This entry was posted in Earth Sciences. Bookmark the permalink.

18 Responses to A WT? Moment

  1. John F. Hultquist says:

    Not enough information.
    Post a photo of the layout.
    Is the plate glass window new — what is in between the layers?
    Looking through a new high-tech (Pella) patio door, I see lights that appear to be out back in trees 100 feet from the house. I have to outen (my mother’s word) inside lights to get the ones outside to go away. I think it has something to do with the layers of glass, their separation, and maybe the gas therein.

  2. seabrznsun says:

    I’m probably one of the least qualified to answer, so I’ll guess. Perhaps there’s a slight bevel at the bottom of the glass edge “catching” and reflecting the light that’s off to the side. In addition the bottom of the glass would likely have to be close to the edge of the varnished wood.

  3. jim2 says:

    Did this happen to occur during beer break?

  4. H.R. says:

    Possible side effect of a second cup of Texas Trailboss Coffee?

    Questions: “Tonight” meant pitch dark outside? The CFL was the sole light source? Was there strong moonlight? Are there any Christmas light displays in the neighborhood? Is the effect repeatable every night?

    Also, if it is single pane glass, the edge finish may come into play. Some cut glass edges are unfinished, which means that they would have irregular planes on the edges that might produce a prismatic effect. Some edges are flame-finished, such that the sharp edges of the cut are melted, but the edge remains ‘clear.’. Diamond abrasive wheels are also used to finish the edges. They produce a dull, frosty-looking edge, but there are sometimes stripes – short and long, depending on the wheel setup an the fracture plane – where the abrasive didn’t touch the glass. The clear patches on glass edges can produce internal reflection/refraction.

  5. Power Grab says:

    What was the weather doing at that time?

  6. E.M.Smith says:

    @John F. Hultquist:

    It is a plane single pane ordinary non-coated glass window from about 60 years ago when the house was built.

    The light source is a CFL bulb in a lamp w/shade located about 7 feet off the ground at a 45 degree angle and about 10? feet from the door. The window is directly opposite the door and about 25 feet away. There is nothing between any of them.

    As the specular bits are a yellow color, I think what may be happening is the light is reflecting between the varnish on the door and the door jam and some spots may be “just right” to make a kind of corner reflector. Tonight I’m going to go stand AT the window (instead of 1/2 way between window and door a couple of feet off axis) and see if the window is only involved as a reflector to me, the viewer, who can’t seeae it directly from the door off axis…


    Nothing of interest. Cool and mild wind but not much.


    Beer was not involved… thought that’s a good suggestion to try tonight ;-)


    The reflection comes from the middle of the glass and it’s about 4 feet tall x 8 feet long. I think the edges are not involved (at least not the glass edges) but the idea of edges on the varnished door is similar in concept…


    Not quite “pitch black” but significantly dark. Trees directly opposite the window and only very limited street lights a couple of hundred feet away, so very limited refection off dark leaves. Nothing like the very bright specular bits. As I moved a little back and forth, the spots of light either went away or would change where they are. Thinking about that has led me to think the window is only involved to make it visible off axis. To be checked tonight…

    CFL the only light source. No moon visible, and the moon is white, this was gold colored specular much brighter than full moonlight. No Christmas lights visible from the back yard (and not much in the neighborhood yet anyway).

    We’ll find out if it is repeatable night to night tonight. ;-)

    Oh, and no Texas Traillboss Coffee was involved; but also a nice idea for tonight ;-)

    The “edge” where the sparkle shows up is the hinge edge of the door to the garage, directly opposite the window. So I think it is the white door jam and the varnished door interacting somehow to make a corner reflector of some sort that lets the CFL bulb be visible in tiny dots along that edge. I’m going to test this theory tonight by moving directly on axis and look AT the door directly, then try blocking the light source (will need a second person) with a small block and moving it up and down a few feet away from the bulb. IF each specular spot extinguishes as the “block” moves over the line to the lamp, then I’ll have proven:
    1) It is the door making the speckles and the window is only to put my off axis view on axis by reflecting it to me.
    2) The lamp placement is important to each “speckle”.

    IF that happens, then I’ll proceed to a closer inspection of the hinge line to see what I can figure out there.

  7. Larry Ledwick says:

    Also, if it is single pane glass, the edge finish may come into play. Some cut glass edges are unfinished, which means that they would have irregular planes on the edges that might produce a prismatic effect.

    That is what I was thinking – total internal reflection inside the corner edge of the glass like a right angle prism. Every time I have seen some sort of effect like that if I carefully positioned myself along the exact axis of the light travel I could see the same thing with the naked eye and identify the exact mechanism of the reflection. Could also be a light source reflecting off the internal edge surface of the glass pane that is/was outside the field of view such as a car head light. down the street that just happens to be in the right location to produce the glint.

    Not to mention unusual reflection conditions or light sources like aircraft landing lights that just happen to be in the right location when you were seeing the effect.


  8. beththeserf says:

    Its Xmas! Probably there’s a religious explanation, EM.

  9. R Shearer says:

    CO2 could do that. It can do anything.

  10. Ossqss says:

    Might be some imperfections in that 60 year old flowing glass? Perhaps some inward reflective outward points, or something you ate? ;-)

  11. E.M.Smith says:

    And the answer is…

    There is a very fine gap between a fence post and the next board in the far back fence. This lines up with some light from the neighbors back yard. As the gap is very narrow and deep, the lights only show up on one exact line when looking out the window. That line aligns perfectly with the reflection of the back door hinge edge.

    That led to the illusion it was the door that sparkled when it wasn’t.

    I’m not sure what light the neighbors are running, but they have sliding glass doors there so it could be anything in their living room.

    Earlier in the evening there was NO light at all, and it only returned later in the evening with their lights on. For a little while I thought it had “just gone away”…

    When it returned I rapidly figured out I could stand “on the line” where it would be a reflection, but still see it in the window with me in the reflection. ( I had to get close to the window to get a wide enough path block as my viewing angle from before put me off the line of reflection (were one happening).

    It was on the walk to the window to get a closer look at the “reflection” that I realized it could not be one, and then carefully observed just where it was coming from with a clearer view.

  12. John F. Hultquist says:

    Not fair!
    You did not tell us the stinking neighbors were involved. Had we known . . .

    Be of good cheer.

  13. jim2 says:

    It’s good to know that Physics has been saved from the Dust Bin of History!! :)

  14. E.M.Smith says:

    @John F. Hultquist:

    How could I tell you what I did not know until I knew it?…


    Yes, much happier now to know Physics is still my friend and it was my lack of initial observation skill that caused the confusion. Leaping off a cliff of conclusion too soon…

  15. H.R. says:

    To very , very loosely paraphrase Sir Arthur Conan Doyle, “Once you’ve eliminated everything else, only the truth remains.”

  16. R. de Haan says:

    Glass remains a fascinating material.

  17. E.M.Smith says:

    @R. de Haan:

    Yes it does… It gave a beautiful reflection of the relatively well lit door to the garage, yet the back yard fence was so dark as to blend into a general black affect. Then the specular bright spots, brighter than anything else, came through it without hint that it was a transmission source not a reflected on. The net effect was bright yellowish spots like specular reflections from the door edge.. composited in the window reflection.

    They do that in movie making and I know about it; I ought to have thought of it quicker…

  18. DonM says:

    I think Beth is correct; per Suzuki, the CO2 in the glass heats the interior of cars so it shouldn’t be any different for your house. The glimmer must the CO2 in the glass slowly releasing its energy during the night. Maybe professor Suzuki could further enlighten

Comments are closed.