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The shadow blister effect is a visual phenomenon in which a shadow bulges (or blisters) as it approaches another.
The effect takes place when two objects are at varying distances between a non- point light source and a background upon which their shadows are cast. As the objects move transversely such that their shadows approach each other, the one nearest the light source begins blocking light from reaching the inside of the other object's - Ray Theory Analysis of the Shadow Blister Effect
/ref> The shadow blister effect is commonly misconceived to be an illusion caused by the combining of the two object's penumbras, aided by factors such as diffraction, nonlinear response, and the eye's inability to differentiate between varying contrasts.
Ray diagram of overlapping penumbra
Optical phenomena
The shadow blister effect is a visual phenomenon in which a shadow bulges (or blisters) as it approaches another.
The effect takes place when two objects are at varying distances between a non- point light source and a background upon which their shadows are cast. As the objects move transversely such that their shadows approach each other, the one nearest the light source begins blocking light from reaching the inside of the other object's penumbra
The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast.
...
, thereby expanding its umbra
The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast. ...
. This expansion of the further object's umbra continues until the umbras of both objects meet.
This effect can be demonstrated and understood using ray theory./ref> The shadow blister effect is commonly misconceived to be an illusion caused by the combining of the two object's penumbras, aided by factors such as diffraction, nonlinear response, and the eye's inability to differentiate between varying contrasts.
See Also
*Black drop effect
The black drop effect is an optical phenomenon visible during a transit of Venus and, to a lesser extent, a transit of Mercury.
Description
Just after second contact, and again just before third contact during the transit, a small black "tear ...
References
{{reflist, smallExternal links
Ray diagram of overlapping penumbra
Optical phenomena