Everything you need to know about daylight saving

23 March 2018
Origins, misconceptions and facts about daylight saving time
Daylight saving is a ritual observed by over 40 percent of the world, but why do we change our clocks and how does it impact your sleep? University of Sydney experts explain.

As we prepare to set our clocks back an hour on 1 April, we asked academics to dispel the myths behind the time change to help us understand its relevance today, over 100 years since it was first observed in Germany during World War I.

Daylight saving is a result of the earth’s tilted rotation around the sun

“The Earth's axis of rotation is tilted, which means that the sun rises and sets at different times throughout the year as the Earth moves around the Sun,” says Professor Tim Bedding from the School of Physics. “The result is that days are longer in summer than in winter.”

“The effect of daylight saving time (DST) becomes less as you move towards the equator, which is presumably why Queensland decided not to adopt daylight saving.

“Without adjusting the clocks, we would find sunrise in Sydney varying from about 4:30am in summer to 7am in winter. Given this variation, we put the clocks forward by one hour during summer months, so that the earliest sunrise is about 5:30am.

“As a result, it remains lighter in the evening during daylight saving time, the sun sets at around 8pm.”

All four southern states observe daylight saving

“Plebiscites have been held on daylight saving in Western Australia in 1975, 1984, 1992 and 2009, with a majority voting ‘No’ each time.  Queensland also voted ‘No’ in 1992,” says Professor of Constitutional Law, Anne Twomey, from the University of Sydney Law School.

“The consequence is that both Western Australia and Queensland do not currently have daylight saving, as is also the case in the Northern Territory. In contrast, New South Wales voted ‘Yes’ in 1976 and South Australia voted ‘Yes’ in 1982, so all four southern states have daylight saving.

“While some regard the different time-zones as annoying, they actually reflect one of the great benefits of federalism – that people in different geographical parts of Australia can choose the system that best suits their own circumstances.

“In a large geographically and climatically diverse country, one size does not necessarily fit all and should not be imposed upon all.”

The time change impacts our sleep and circadian rhythm

“Moving our non-biological clocks by an hour due to daylight saving time (DST) shifts our daily activities and thus the exposure to light and other time cues relative to our internal circadian clocks. This introduces a minor circadian misalignment,” says Dr Sveta Postnova a Lecturer in Brain Dynamics and Neurophysics from the School of Physics.

“Relative ease of adjustment to minor time changes are assumed by the general population, however scientific data does not support this.

Man struggling to sleep.

“For the spring transition with one-hour sleep loss on the night of the transition, experimental data suggests a cumulative effect of sleep loss lasting for at least the following week and sometimes longer. The autumn transition is popularised as adding one-hour to sleep time, but data shows no evidence of extra sleep on that night.

“Instead, cumulative sleep loss is also reported in the days following the transition. Overall, DST appears to interfere with natural physiological adaptation to seasonal changes.”

Internal clock misalignment may affect eating temporarily

"Pushing the clocks forward an hour results in a misalignment in our internal biological clock – otherwise known as our circadian rhythm," says Dr Nicholas Fuller, a weight loss expert from the Charles Perkins Centre.

"This is a temporary effect, but when it comes to food, you may find yourself eating later in the evening and doing other activities to fill the daylight hours. This can have a flow on effect, especially if you’re a morning lark and like to get to bed early, and particularly relevant for those who already suffer from digestive problems. If you eat close to bedtime, it can acerbate problems with digestion and reflux, worsening your sleep.

"Try to stick to your normal routine when it comes to portion sizes to improve sleep quality and weight control, make breakfast your largest meal of the day and dinner your smallest."

A farmer's harvest is not affected by daylight saving 

“Farmers' harvest based on the moisture content of the grain, or, if harvesting pastures for hay or silage then it’s the moisture content of the grasses and plant species in those pastures that’s important. The time of day is irrelevant,” says Dr Lindsay Campbell, a Senior Lecturer from the Sydney Institute of Agriculture.

“It’s temperature and humidity that will affect harvesting most rather than time. This is why you will sometimes see our farmers at Narrabri out with the lights on after 8pm harvesting. Artificial lighting can be utilised to ensure harvesting occurs at peak turgidity.”

Cows like routine but prefer independence and freedom 

“Cows like routines and therefore any sudden change (for example, milking one hour earlier) will be noticeable in terms of milk production,” says Yani Garcia, a Professor of Dairy Science and Director of the Dairy Research Foundation at the University of Sydney School of Veterinary Science.

“However, milk secretion in the mammary gland is a continuous process. Provided no changes in total feed availability, the effect of a change to milking intervals should be compensated in the next milking and/or become unnoticeable in just a few days.

“Our research in robotic milking, where cows get milked by robots whenever they want during day or night, show that cows like more the independence and freedom than the actual routine,” says Yani.

“Given the choice, some cows would come back to get milked 3 or more times per day, while some others prefer only once or 3 times every 2 days and anything in between.”

Daylight saving better aligns power consumption

“Daylight savings shifts the power consumption an hour forward, so demand is better aligned with solar insolation,” says Associate Professor Gregor Verbic from the Centre for Future Energy Networks in the School of Electrical and Information Engineering.

“You don’t turn your air conditioning off when the sun goes down on a hot day,” explains Professor Verbic, so it’s not necessarily accurate to suggest air conditioning use will increase as a result of daylight saving – you're probably running a cooling system regardless.

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