Exaggeration of shadows in flat icons and death of purpose.

icon_shadows
You see them?
Flat colors, perfect symbols, beautiful proportions but exaggerated shadows. When we talk about physics, flat icons and lights, how can someone miss the point that shadow is NOT DEPTH.

Shadow is misleading.
Its beautiful BUT misleading.

what do you see first?  shadow or child ? via

Shadow depends on lights, angle and material type. Sharp shadow means sharp and single light source, faded shadow means weak or multiple light sources.

Shadow of wall with a glass window via

Human eyes perceive depth by texture, angle, color effects and THEN shadow of the object.

glass
Wall without shadow is still a BIG WALL.
via
Glass has no texture and light travels through it.
via

Even if I create a miniature of left image and present a photograph, you can quickly co-relate it with a wall and can tell that it is big and thick.
However, in case of glass which has no texture and allows light to pass through it, you cannot co-relate it with anything and therefore cannot tell the depth of it. You cannot tell thickness of glass just by looking through it or shadows, you need angle, edges and something near it for comparison.

Coming straight to the point, if a designer assumes that depth of an object or symbol is by its unreal, extra long casted shadow which is almost 2 times the length of object/symbol; then it is a major design flaw and exaggeration. If you want to cast shadow, consider light effects on object too.

comparison  of various icons
Lights and shadows should be proper and  natural to provide depth.
A quick comparison.

What users see:
what user sees

Few brands who misunderstood this design philosophy :
flipkartblunder

Flipkart.com: one of the major online shopping websites of India.

Conclusion:
You can find thousands of articles about casting extra long shadow using photoshop or illustrator and I admit some of them are truly beautiful.

However, slightest modification in shadow can save or kill the purpose. So use it wisely and create natural and appealing icons.