Fill flash is when you are outdoors for example and the light you are getting from the sun is the main light. Fill flash is just that.

现在来谈谈闪光灯补光，补光是指当你在户外，阳光是主要光源时，闪光灯用来照亮阳光给人物带来的阴影等影响(如兔眼等)。

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This time the flash fires just the right amount of light to "fill-in" the subject with the flash produced light. Now you have a rather nice shot where you can see the subject and the background.

然后你再次拍下照片，闪光灯发出刚够照亮拍摄主体的闪光，这一次的照片要好多了，你可以同时看清主体和背景。

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During pairing, red light and blue light flash alternatively. If pairing failed, blue light will flash once per 2 seconds.

配对时，红蓝灯交替闪烁。配对失败后，篮灯每2秒闪烁一次。

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He said he could see the flash of light from Confederate guns along a line a kilometer long.

VOA: special.2009.12.17

To get creative in challenging light, a built-in pop-up flash supplies extra lighting when capturing images in low-light situations or to provide a fill flash to eliminate shadows.

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Battery cells, by the way, refer to products such as the conventional AA batteries inside a flash light.

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There was a quick flash of light and then I knew all that he knows.

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