The “Dark Mode” of Apple Inc’s iOS13 mobile operating system is pictured in this screen grab. 蘋果公司iPhone的iOS13作業系統推出黑暗模式。 Photo copied by Wu Pei-hua, Liberty Times, from Apple Inc’s official Web site. 照片：自由時報記者吳佩樺翻攝自蘋果官網

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Many smartphone screens switch to warmer colors in the evening to help you sleep better — but research suggests the science behind this is all wrong.

“Night mode” is one of those features you may be aware of only because your phone keeps telling you about it. At some point while you are lying in bed at night sending texts, your screen may politely suggest you activate a function that shifts the colors of your screen from the colder to the warmer end of the spectrum. It is supposed to help you sleep better.

Findings in a study led by Tim Brown, a scientist from the University of Manchester, and published in Current Biology suggest this is the very opposite of correct. The research, carried out on mice, appears to rubbish the notion that blue light disrupts sleep. All things being equal, warm yellow light is worse.

So, where did the idea of limiting blue light from screens originate? “There was definitely a valid scientific idea about why those things would work,” says Brown. It started about 20 years ago with the discovery of the role that melanopsin — a light-sensitive protein found in the eye — plays in regulating the body clock.

“The melanopsin system is fundamentally there to detect brightness,” says Brown. Because melanopsin was better at detecting short-wavelength photons, he says, it was thought it was biased in favor of blue light. In fact, it is the retina’s cone cells that determine color. “The cone system also plays a role, and they’re doing the opposite of what most people thought,” says Brown.

According to the study, brightness levels are more important than color when it comes to stimulating the body clock. However, when the light is equally dim, blue is more relaxing than yellow. This makes basic sense: daylight is yellow, twilight is blue, and sunrise and sunset are pretty reliable ways to tell your body clock what time it is. Of course, at this point, we only know it works on mice — and mice don’t have phones. “We think there is good reason to believe it’s also true in humans,” says Brown.

There is perhaps a more obvious truth to be drawn — if your phone is telling you to switch to night mode, it is time to put down your phone. It is not the color of the screen that is keeping you awake; it is all the stuff your phone offers as an alternative to sleep at 2am. There is only one real night-mode switch: the off button.

（The Guardian）

許多智慧型手機螢幕會在晚上切換成較溫暖的顏色，來幫助使用者睡得更好。然而，最近一份研究顯示，這項功能背後的科學根據完全是錯誤的。

「夜間模式」是一種只有在手機不斷跳出提醒時，你才會注意到的功能。當你晚上正躺在床上傳訊息的某個時間點，手機螢幕也許會禮貌性地建議你開啟一項功能，讓手機螢幕的顏色從較冰冷的色調切換到光譜上較溫暖的那一端。這個設計據稱是為了讓你睡得更好。

由曼徹斯特大學的科學家提姆‧布朗主持，並發表於期刊《當代生物學》的這份研究指出，事實恰好相反。該研究以老鼠做為實驗對象，似乎抨擊了「藍光干擾睡眠」的概念。研究認為，在所有條件不變的情況下，溫暖的黃光其實更妨礙睡眠。

那麼，限制手機螢幕發出藍光的想法是從哪裡來的呢？布朗表示：「過去確實有可信的科學觀點，解釋那些功能為什麼有效。」這類觀點來自於大約二十年前，科學家發現「視黑蛋白」──眼睛裡的一種感光蛋白質──在調節生理時鐘時扮演的角色。

布朗指出：「視黑蛋白系統在眼睛裡最根本的作用是偵測亮度。」他進一步解釋說，因為視黑蛋白偵測短波長光子的能力較佳，所以當時認為這種蛋白質較容易受藍光影響。事實上，視網膜的錐細胞才是真正決定顏色的器官。他表示：「錐細胞系統也參與了調節生理時鐘的機制，而它們的運作方式其實跟絕大多數人以為的完全相反。」

根據這項研究，就刺激生理時鐘的層面而言，光線的亮度其實比顏色還來得重要。不過，在光線同樣昏暗的情況下，藍光其實比黃光更能讓人放鬆。這是很有道理的：日光是黃色的，薄暮則呈現藍色，而日出與日落更是非常可靠的方式，讓你的生理時鐘知道現在的時間。當然，在這個階段，我們只知道這項觀點能在老鼠身上驗證──而老鼠卻沒有智慧型手機。布朗表示：「我們認為仍然有充分理由可以相信人類也是如此。」

我們也許還能推論出一項更明顯的事實──當手機提醒你將螢幕調整為夜間模式時，就是該放下手機的時候了。並不是手機螢幕的顏色讓你一直醒著，而是手機提供的所有東西，在凌晨兩點鐘構成你睡覺之外的另一個選項。其實，真正的「夜晚模式」開關只有一種，那就是手機的關機鍵。

（台北時報章厚明譯）

TODAY’S WORDS

今日單字

1. rubbish v.

抨擊

（peng1 ji2）

2. all things being equal phr.

所有條件相同

（suo2 you3 tiao2 jian4 xiang1 tong2）

3. valid adj.

可信的

（ke3 xin4 de5）

4. light-sensitive adj.

感光的

（gan3 guang1 de5）

5. body clock phr.

生理時鐘

（sheng1 li3 shi2 zhong1）

6. retina n.

視網膜

（shi4 wang3 mo2）

新聞來源：TAIPEI TIMES

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