Photo: The Canadian Press. All rights reserved.

This 2009 photo released by NBC shows Brian Williams on the set of "Nightly News with Brian Williams," in New York. ABC, CBS, NBC evening newscasts had 11 percent fewer viewers because of the time change and longer days. The Nielsen company says the newscasts collectively had 11 percent fewer viewers last week than they did the week before. (AP Photo/NBC News, Justin Stephens)

Despite a busy week with the selection of a new pope, the ABC, CBS and NBC evening newscasts collectively had 11 per cent fewer viewers than the week before — and a glance outside the window reveals the primary reason why.

The simple act of moving the clock ahead one hour for daylight saving time is costly for the broadcasts, since the hour that turns from darkness to light happens to be the hour in which they are shown in most of the country.

It's not just a one-week phenomenon. The newscasts will have to deal with smaller audiences until the clocks are pushed back in the fall.

"What it shows is that a large proportion of the people that watch the news are not watching because they watch the news," said news consultant Andrew Tyndall. "They're watching it because they happen to be home when the news is on."

Both NBC's "Nightly News" and ABC's "World News" lost a million viewers from week to week, the Nielsen Co. said. The "CBS Evening News" lost 600,000. That's a total of 2.6 million, or a little more than the entire audience for the NBC sitcom "Community" last week.

While the situation isn't unusual, each newscast lost more viewers in the week-to-week comparison than they did between 2012 and 2011.

"This is part of a predictable cycle every year, so we know to expect a slight dip in viewership when people are enjoying longer hours of daylight," said Patrick Burkey, executive producer of "Nightly News." ''We approach the broadcast with the same mission every day regardless of what time the sun sets."

"Nightly News" had an average of 8.1 million viewers last week (5.4, 11). ABC was second with 7.2 million (4.9, 10) and CBS had 6.4 million viewers (4.3, 9).