This morning when I woke up I observed a surprising phenomenon… my ceiling fun appeared to have only three blades instead of four! The diffused ambient light from my curtained windows matched the same light level of the “missing” blade which made it visually disappear.

Variable light brightness can be used to blend items with their background and disguise the otherwise obvious silhouette.

This effect of counter-illumination was experimented with as early as 1916 and later during wartime in 1943 for military purposes and became known as Yehudi lights. These lights were mounted on aircraft and also projected onto ship hulls that automatically adjusted light brightness to match the background behind it.

It is interesting to note that this phenomenon also exists in nature in some squids, fish, and shrimp that have bio-illuminecent features, thus diminishing their silhouette.

This causes one to ponder what similar applications could be employed that might help to conceal private property or location to avoid attention or detection. Unlike the use of images or patterns, Yehudi lights would require power for illumination but might be more adaptive in their particular environment.