Clocks will soon "fall back" for the end of daylight saving time this week, but when exactly will the time change?
Under the conditions of the Energy Policy Act of 2005, daylight saving time starts on the second Sunday in March and ends on the first Sunday in November. On those days, clocks either shift forward or backward one hour.
This year, the end date will fall on Nov. 3, with clocks rolling back one hour at 2 a.m., giving Illinoisans an extra hour of sleep.
Here's what to know:
What happens after the time change?
The end of daylight saving time will mark a transition back into standard time in Illinois.
Standard time, according to Time and Date, "is the local time in a country or region when Daylight Saving Time (DST) is not in use."
In some countries, standard time is known as or winter time or normal time. Daylight saving time is then referred to as summer time.
"More than 60% of the countries in the world use standard time all year," the site says. "The remaining countries use DST during the summer months, generally setting clocks forward one hour from standard time."
When does daylight saving time start again?
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Daylight saving time will make its return to the Chicago area on March 9, the second Sunday in March.
By that point, the city will be experiencing nearly 12 hours of daylight again, and sunset will occur just after 7 p.m.
Which states don't observe daylight saving time?
The annual time change will occur in Illinois and nearly every U.S. state, except two:
Arizona (although some Native American tribes do observe DST in their territories) and Hawaii.
U.S. territories, including Puerto Rico, American Samoa, Guam and the U.S. Virgin Islands, also do not observe daylight saving time.
Why do we change the clocks every year?
Daylight saving time has been around for more than 100 years; it was originally established in 1918 to save energy costs during World War I, according to the Library of Congress. The law was repealed about a year later due to the war's end but implemented once again during World War II. It was instated to help conserve fuel and "promote national security and defense," and as a result, called "war time."
The law was repealed a second time, following the war's end, to allow states to establish their own standard time, the Library of Congress stated.
Daylight saving time later became standard in the U.S. until the passage of the Uniform Time Act of 1966, which mandated standard time across the country within established time zones.
What's better: Daylight saving time or standard time?
The topic of daylight saving time vs. standard time has been hotly debated, particularly in recent years when legislation proposed the possibility of switching to a permanent daylight saving time.
Sleep experts have advocated in some cases for a permanent standard time. But some experts say switching to permanent daylight saving time would be worse.
"Permanent standard time would basically mean that we were on what is, I guess, biologically the correct time all year round. And I'm going to say biologically correct because our bodies are more used to and have evolved to be on what would be considered standard time over the years," Dr. James Rowley, a professor of medicine at Rush University and the immediate past president of the American Academy of Sleep Medicine told NBC Chicago in an interview. "Permanent daylight saving time, the particular problems come in at winter. It is great to have 'the extra hour of sunlight' in the evening, although I always remind people, we have the same amount of sun, you know, in the summer, whether it's daylight or standard time, but just that seems to be an hour later. But in the winter time, sunrise is much later, and that's very problematic biologically, because we need sunshine in the morning to set our circadian rhythms for the day."
Previously, proposed legislation pushed for permanent daylight saving time, but that legislation ultimately fell through and no new legislation has been proposed for a vote.
So, clocks continue to change twice each year.
The American Academy of Sleep Medicine has pushed for a switch to permanent standard time for several years.
“By causing the human body clock to be misaligned with the natural environment, daylight saving time increases risks to our physical health, mental well-being, and public safety,” Dr. M. Adeel Rishi, who is chair of the AASM Public Safety Committee and a pulmonary, sleep medicine, and critical care specialist at Indiana University Health in Indianapolis, said in a statement. “Permanent standard time is the optimal choice for health and safety.”
Experts cited a "growing body of evidence" in recent years.
“Permanent standard time helps synchronize the body clock with the rising and setting of the sun,” Dr. James A. Rowley, president of the AASM, said in a release. “This natural synchrony is optimal for healthy sleep, and sleep is essential for health, mood, performance, and safety.”
It also mirrors similar takes from other organizations, including the National Sleep Foundation, which said "seasonal time-changes are disruptive to sleep health and should be eliminated."
Permanent daylight saving time would lead to later sunrises across much of the U.S., with some states not seeing a sunrise until after 9 a.m. during portions of the year.
"Having sunshine in the morning actually helps us to fall asleep at nighttime. And the other problem is, of course, it's darker later into the morning, which has its own set of problems with safety, driving, people walking. Parents are definitely worried about their kids walking to school in the dark," Rowley said. "If we were on permanent daylight saving time, most of the United States would not have sunrise until after 8 a.m. and the northern states - you know, the particularly northern states like Minnesota, Montana, the Dakotas - would not have sunshine until after 9 o'clock in the morning. And so the American Academy of Sleep Medicine firmly believes that we should be on permanent standard time, not permanent daylight saving time."
Still, Rowley noted that no legislation is currently being discussed to push for a switch to permanent daylight time, so a change in the near future is unlikely.
With clocks still changing, Rowley noted that growing evidence appears to suggest the body never fully adjusts to daylight saving time - even between spring and fall.
"Losing that hour of sleep [in the spring] for some people, just makes them more anxious, some more depressed, some more irritated. So it can be quite problematic. Problem is that, even long term, while we think we are adjusting to that change, there is actually evidence that we don't completely adjust to the change, so we are still at increased risk for all those things throughout daylight saving time," he said. "Plus, as I mentioned before, we need sunshine in the morning to help us fall asleep at night. But during the summer, if we have light too much late into the evening, that actually prevents us from falling asleep. So having that 'extra light' in the evening actually prevents sleep. So it just has its long term consequences as well."
