Light has a predominating influence in setting the clock.

在设置时钟时，光起着主导作用。

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You program the clock with the latest time at which you want to be wakened, and it then duly wakes you during the last light sleep phase before that.

你给时钟设定了你想要醒来的最晚时间，然后它会在之前的浅睡眠阶段按时叫醒你。

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Use blinds or blackout curtains to keep out light. Switch off or cover anything that emits light, such as an alarm clock.

在睡前灯光越暗越好，最好是一点灯光也没有，用一些黑色的窗帘阻挡灯光，替换所有会吸光的东西，如会发光的钟。

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Even relatively small amounts of light can reset the body's internal clock, so find as dark an environment as possible when traveling.

CNN: Sleep tips for the road-weary

If the climate or hour of the day at the new destination don't allow for lots of light, a small, portable light box, some of which double as an alarm clock, can be purchased.

WSJ: To Avoid Jet Lag This Summer, Travel Like a Scientist

Evidence of past explosions is revealed in the image - huge lobes of 20-million-degree Celsius gas (the red loops in the image at approximately the 2 o'clock and 7 o'clock positions) that extend over dozens of light-years on either side of the black hole.

BBC: Black hole 'on a diet'