What are the traditional rules for drop shadow direction / light source?


When creating a drop shadow for objects, what is the traditional / classic "rule" for the offset direction? I see so many that are down and right, which results in the light source coming from the top left.

However, I read somewhere (I don't remember where, maybe an old David Siegel post from years ago) that when adding drop shadows to text, the shadow offset should be down and left, which provides a slight dark edge to the leading edge of the text, enhancing readability.

Or is the rule just "be consistent"?

Just to be clear, I'm asking if there's a design "principle" that has been established through tradition or precedence.

11/6/2012 1:09:00 PM

Accepted Answer

In your designs of your own devising, be consistent. If one object has a top-left light source, then all of your objects should have a top left light source.

In designs of others's devising, you need to be consistent with their format. In the case of Apple's Mac OS X (per the HIG), drop shadows come from the top-center, and actually a bit on the front around a 45Ëš angle, and not from the side.

As for the direction, that is largely dependent on the effect you are trying to achieve, but as an informal rule based on not-so-casual observation, the light-source is typically on the top-left casting a bottom-right shadow. David Siegel may technically be correct, but it is almost entirely subjective in the end.

3/31/2011 2:47:00 PM

From kindergarten to elementary school the majority of my (and other kids') drawings had a thing called "corner Sun" which was a quarter of the Sun filling the upper-left corner. At first this analogue might sound far–fetched or tongue–in–cheek, but I think the concept of corner Sun points to the source where the idea of ideal drop shadow comes from.

Now, I was about to post a Google image search on the topic to enhance my point, but noticed a notable amount of drawings having the corner Sun in the upper-right corner! So generalizing directions ought to be taken with a pinch of salt* . I have a hunch that there might be either cultural or even left/right handedness connections—but I have no studies concerning the origins of the corner Sun. Definitely would read those.

What is the most common, however, is that the light is coming from upper left.

I think the main reason for this isn't derived from the concept of an ideal drop shadow, but from the cold fact that Photoshop has the default drop shadow direction set to 120° by default or to be more specific: the global light value is set to 120°. This looks adequate for most cases so why bother questioning the value every time. Adobe's reasoning for this very angle value would be interesting to hear.

*) Well, duh, as always