# Might a Lamp Light More Bright in the Night? **URL:** \ **Category:** Factual Questions\ **Created:** [October 18, 2010, 12:34am UTC](https://boards.straightdope.com/t/might-a-lamp-light-more-bright-in-the-night/557499 "2010-10-18T00:34:43Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![bienville](https://avatars.discourse-cdn.com/v4/letter/b/4bbf92/32.png) [@bienville](https://boards.straightdope.com/u/bienville)\ **Post date:** [October 18, 2010, 12:34am UTC](https://boards.straightdope.com/t/might-a-lamp-light-more-bright-in-the-night/557499/1 "2010-10-18T00:34:43Z")
I am sure, I am sure, this _must_ just be a matter of perception . . . like those graphics of light and dark lines that are of the same width but look like the light ones are wider (or the dark ones are wider, I forget how that works) . . . but my perception of this matter tells me it’s true, true, true! even as my rational mind argues that there is no reason why it should be true. There’s a couch with a lamp next to it. Neither the couch nor the lamp move, we don’t change to a stronger bulb at 6pm every day. There are no variables other than the amount of incidental light from daytime and nighttime. When I sit on the couch to read a book, I sit in the exact same spot, right under the lamp. If I sit down to read during the day, as daylight comes in through the windows, it is a bit of a strain on my eyes to read the print- even as I sit under the lit lamp. Sitting in the same spot under the same lamp at nighttime, with no daylight creeping in, with absolutely no additional light source other than this lamp, the page is brightly illuminated and the text is easy to read. Why? Is is just a matter of perception? Because the rest of the room is dark, the page _seems_ to be more brightly lit? Or is the page, indeed, more brightly lit? Is there some complex principle of Physics whereby the light from the lamp is dissipated by the daylight, scattered more broadly and away from the page? I do strongly suspect it is just a perception thing, like how one line of text in a book run over with a highlighter would stand out brightly (lamp on book in a dark room), while all the lines of text run over with a highlighter would not seem so bright (lamp on a book in a bright room). Still, it really _seems_ like it’s true that the book is more brightly illuminated at night. What up? ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 18, 2010, 12:45am UTC](https://boards.straightdope.com/t/might-a-lamp-light-more-bright-in-the-night/557499/2 "2010-10-18T00:45:46Z")
The watts/m[sup]2[/sup] don’t change so the intensity remains constant. What doesn’t is the size of your pupil which can go from 4mm across to 8mm across. Basically the area allowing light in increases by a factor of 4. ---
**Author:** ![falcotron](https://avatars.discourse-cdn.com/v4/letter/f/3ab097/32.png) [@falcotron](https://boards.straightdope.com/u/falcotron)\ **Post date:** [October 18, 2010, 12:48am UTC](https://boards.straightdope.com/t/might-a-lamp-light-more-bright-in-the-night/557499/3 "2010-10-18T00:48:55Z")
Remember that your eyes can adjust to the amount of light. Daylight is a lot brighter than your lamp. So, when your eyes are adjusted to daylight, the lamp-lit page is dark. The night is a lot darker than your lamp (or, if you’ve got the indoor lights on, about the same brightness as your lamp). So, when your eyes are adjusted to that, the lamp-lit page is bright. More immediate contrast effects, as you suggest, may have something to do with it as well, but I’m not going to bring that up after making such a big mistake in another thread. 🙂 ---
**Author:** ![bienville](https://avatars.discourse-cdn.com/v4/letter/b/4bbf92/32.png) [@bienville](https://boards.straightdope.com/u/bienville)\ **Post date:** [October 18, 2010, 1:09am UTC](https://boards.straightdope.com/t/might-a-lamp-light-more-bright-in-the-night/557499/4 "2010-10-18T01:09:13Z")
Whoah, that explanation actually makes total sense to me. Thanks!