Brewsters Fringes

Brewsters Fringes
The appearance of the optical phenomenon known as Brewster’s Fringes is not a defect of the glass, and can occur with any glass of high optical and surface quality.
Thisphenomenon is a result of the high quality now being achieved world wide by modern methods of glass manufacture. Brewster’s Fringes occur if wavelengths of
light meet up with each other when they are exactly180º out of phase – an example of the phenomenon known to physicists as the interference of light.
The effect is similar to, although usually much smaller than the interference fringes which cansometimes be seen on toughened glass windscreens.
Interference fringes are a series of faint, irregular, roughly parallel lines, which are grey or colored, and are sometimes visible in clear insulatingglass (IG) units.  They are typically a fraction of an inch wide and many inches long.  They are caused by interference effects when light waves reflect from parallel, or nearly parallel glasssurfaces.
Interference fringes are caused by reflections between the various glass surfaces of an IG unit when one light wave is delayed relative to another. Fringes are seen because of the constructive ordestructive interference which occurs when two light waves combine. If the waves are in phase the resulting light will be stronger and brighter.  If the combining waves are in opposite phases theycancel each other and the resulting light is weak.
The easiest fringes to see are the colorful Newton’s Rings which occur when the two glasses of an IG unit touch at the center.  The contacting glassarea will be surrounded by concentric curving fringes.  Tapping on the glass usually has no effect on these fringes because the glass to glass contact prevents any change 
in the geometry of thereflecting surfaces.
These fringes are caused by the slight delay between two light waves reflected from the two surfaces on either side of the very narrow tapered air gap, resulting in 
constructive or...