I did not realize that the dull overcast day is the best time for outdoor portraits until I saw my pictures taken on such a day. Natural instincts told me that a sunny day would be a better choice. However, this is true only for our eyes, and not for the camera. For the camera, direct sunlight is too harsh.

The following two are pictures of the same courtyard of a college campus. The picture on the right was taken on a sunny day, the one on the left on an overcast day:

 
To our eyes, overcast days are dull looking (left). Sunny days are more exciting and vibrant.

The next two pictures show how a portrait would look like when taken under these contrasting lighting conditions:

 
The skin tone of people always looks much more natural on overcast days (left). On sunny days, the shadow areas contrast harshly with the highlighted areas.

On overcast days, the sunlight is diffused by the clouds and becomes soft. In photos, this means that the subjects are lit more evenly and naturally — usually you can see much more pleasant faces in photos. On the right, the direct sunlight on sunny days casts unpleasant shadows on facial features, not to mention the tendency to make people squint.



Pay special attention on overcast days!
Although overcast days are great, we need to be careful if it is too dark:

•	The dimmer condition usually requires slower shutter speed for the correct exposure. Always use a tripod when the shutter speed was slower than 1/45th of a second.
•	Try to find a position where it is brighter than the surrounding. This help the subjects stand out from the background (See our photos taken in Versailles on the right).
•	Not all overcast days are equal. When it is too dark, the resulting pictures can indeed look dull. It happened to us at Loire Valley. Instead of fighting it, we just relaxed, enjoyed the time together; and waited for a brighter day.

How about a sunny day?
When there is too much direct sunlight, there are still something we can do about it:

•	Take photos in the mornings or late afternoons: we took photos earlier in the morning, such as in the first two hours of sunrise, when the morning fog was still there to scatter the sunlight. 1-2 hours before dusk is also good. The sunlight is less strong and its orange-ish color gives a warm feeling to portraits.
•	Find some shadows: we would stand in the shadows of buildings or plants. This approach, however, might result in a high contrast scene, which is generally a challenge for photographers. I leave the details on how to set the correct exposure in this kind of situation in the next section.

 
One of the remedies for sunny days: we could position ourselves in some shadows. Compare to the sunny picture on the right above, there is a clear improvement in the skin tone.