# Sleeping With Light On Cancer Risk? **URL:** \ **Category:** Factual Questions\ **Created:** [October 12, 2012, 2:08pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512 "2012-10-12T14:08:17Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![GreenElf](https://avatars.discourse-cdn.com/v4/letter/g/9de053/32.png) [@GreenElf](https://boards.straightdope.com/u/GreenElf)\ **Post date:** [October 12, 2012, 2:08pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/1 "2012-10-12T14:08:17Z")
I’ve been sleeping without any light, pitch black, since reading somewhere that light during sleep increases the risk of cancer. I’ve regularly awoken around 4 to 6 AM each morning as outdoor light increases, I guess because I’m just so excited to start the new day. Recently, I’ve tried sleeping with my single bulb bedroom lamp turned on, so that I’m not so sensitive to increase in outdoor light during the early morning hours. I’m sleeping longer, even to 8 or 9 AM, so it seems to be working, but should I be concerned about any cancer risk from it? ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [October 12, 2012, 2:13pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/2 "2012-10-12T14:13:32Z")
Cancer from what, exactly? Exposure to light? :dubious: ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 12, 2012, 2:14pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/3 "2012-10-12T14:14:49Z")
A 15W night light is not going to give you cancer. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [October 12, 2012, 2:18pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/4 "2012-10-12T14:18:30Z")
> [@Grey](#): > > A 15W night light is not going to give you cancer. Neither will an opening night theatre spotlight. Though it will ruin your sleep. 😃 ---
**Author:** ![Szlater](https://avatars.discourse-cdn.com/v4/letter/s/90ced4/32.png) [@Szlater](https://boards.straightdope.com/u/Szlater)\ **Post date:** [October 12, 2012, 2:21pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/5 "2012-10-12T14:21:56Z")
> [@runner pat](#): > > Neither will an opening night theatre spotlight. Though it will ruin your sleep. 😃 How much UV do those things pump out? ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 12, 2012, 2:23pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/6 "2012-10-12T14:23:02Z")
But don’t leave an electric fan running all night if you want to wake up in the morning. ---
**Author:** ![GreenElf](https://avatars.discourse-cdn.com/v4/letter/g/9de053/32.png) [@GreenElf](https://boards.straightdope.com/u/GreenElf)\ **Post date:** [October 12, 2012, 2:33pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/7 "2012-10-12T14:33:14Z")
> [@TriPolar](#): > > But don’t leave an electric fan running all night if you want to wake up in the morning. An electric fan helps you to sleep longer? Here’s an article that’s similar to the one I read a few years ago: > **[Shut off the light at night to reduce cancer risk](https://www.naturalnews.com/031087_night_lights_cancer.html)** > > Shut off the light at night to reduce cancer risk It states that a single light source during sleep can alter normal cellular division in the body. My lamp has a 60W bulb. My bedroom doesn’t have a wall outlet to use a night light. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [October 12, 2012, 2:35pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/8 "2012-10-12T14:35:26Z")
Interestingly, I found [this study of sleep-time lighting and its effects on breast cancer.](http://www.ncbi.nlm.nih.gov/pubmed/21605163) It says that yes, nighttime lighting can influence the growth of breast cancer tumors. This mechanism works through receptors in your eyes, which mean that as long as you keep the room lighting dim enough so that you don’t perceive a difference in brightness when you wave your hand over your [closed] eyes, you should be fine. However, OP seems to indicate that he/she is deliberately using illumination that is brighter than that test, so as to mask the early-morning arrival of the sun. As an alternative, I would suggest replacing or augmenting window coverings with blackout fabric (material coated so as to be opaque); this will let you sleep well beyond sunrise without being awoken by bright light. Wife and I did this years ago because the head of our bed was right next to the window, and it makes a big difference. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [October 12, 2012, 2:37pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/9 "2012-10-12T14:37:44Z")
> [@GreenElf](#): > > An electric fan helps you to sleep longer? A lot longer. Like [forever.](http://en.wikipedia.org/wiki/Fan_death) ---
**Author:** ![Szlater](https://avatars.discourse-cdn.com/v4/letter/s/90ced4/32.png) [@Szlater](https://boards.straightdope.com/u/Szlater)\ **Post date:** [October 12, 2012, 2:45pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/10 "2012-10-12T14:45:31Z")
> [@GreenElf](#): > > An electric fan helps you to sleep longer? > > Here’s an article that’s similar to the one I read a few years ago: > [Shut off the light at night to reduce cancer risk - NaturalNews.com](http://www.naturalnews.com/031087_night_lights_cancer.html) > > It states that a single light source during sleep can alter normal cellular division in the body. My lamp has a 60W bulb. My bedroom doesn’t have a wall outlet to use a night light. Yeah, that cite isn’t exactly a reliable source of scientific evidence. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 12, 2012, 3:05pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/11 "2012-10-12T15:05:41Z")
> [@Machine\_Elf](#): > > Interestingly, I found [this study of sleep-time lighting and its effects on breast cancer.](http://www.ncbi.nlm.nih.gov/pubmed/21605163) It says that yes, nighttime lighting can influence the growth of breast cancer tumors. This mechanism works through receptors in your eyes, which mean that as long as you keep the room lighting dim enough so that you don’t perceive a difference in brightness when you wave your hand over your [closed] eyes, you should be fine. > > However, OP seems to indicate that he/she is deliberately using illumination that is brighter than that test, so as to mask the early-morning arrival of the sun. As an alternative, I would suggest replacing or augmenting window coverings with blackout fabric (material coated so as to be opaque); this will let you sleep well beyond sunrise without being awoken by bright light. Wife and I did this years ago because the head of our bed was right next to the window, and it makes a big difference. Which says nothing about “increasing the risk of cancer”. If I’m reading your cite correctly it states only that night time light levels sufficient to disrupt a normal sleep allow for a change in the rate of cancer growth. The cancer is already present. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 12, 2012, 3:22pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/12 "2012-10-12T15:22:45Z")
> [@TriPolar](#): > > But don’t leave an electric fan running all night if you want to wake up in the morning. Only fans in Korea are dangerous. It doesn’t matter where the fan is made, if it goes to Korea it knows to be dangerous. Those fans are sneaky. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 12, 2012, 3:35pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/13 "2012-10-12T15:35:42Z")
> [@Szlater](#): > > How much UV do those things pump out? Depends on the type of bulb. Old fashioned incandescent bulbs put out a very tiny amount but it’s nowhere near enough to worry about for health effects. CFL bulbs put out a bit more. Supposedly CFL bulbs also don’t put out enough to worry about, but a study done last summer found higher than expected levels of UV from every CFL bulb they tested, apparently due to cracks in the bulb’s phosphor coating. The articles I read about it made a big deal about significantly higher UV levels without actually saying what the levels were, so it’s hard for me to tell if there’s anything worth worrying about or if it’s a bit of typical journalist over-sensationalism. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [October 12, 2012, 3:43pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/14 "2012-10-12T15:43:05Z")
If you Google “turning light on at night”, it will autocomplete to “turning light on at night causes cancer” by the time you get to “at”, so plenty of people are obviously aware of this idea. I remember reading an article suggesting that even turning the light on for a minute or two, say to go to the bathroom in the night, increased the risk significantly. Turns out that might not have been strictly accurate… See: [Turning on the Light to Pee at Night Causes Cancer](http://gawker.com/5515697/turning-on-the-light-to-pee-at-night-causes-cancer). And the subsequent [Correction: Turning on the Light to Pee at Night Does Not Cause Cancer](http://gawker.com/5525976/correction-turning-on-the-light-to-pee-at-night-does-not-cause-cancer)… Edit: I don’t think it was about UV light causing cancer on the skin. It was about disruption to the circadian rhythm caused by the body reacting to light levels, IIRC. ---
**Author:** ![wheresmymind](https://avatars.discourse-cdn.com/v4/letter/w/91b2a8/32.png) [@wheresmymind](https://boards.straightdope.com/u/wheresmymind)\ **Post date:** [October 12, 2012, 3:44pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/15 "2012-10-12T15:44:15Z")
What all of these studies seem to be saying is that having a messed up circadian rhythm can negatively affect some aspects of your health (note that as near as I could tell, none of them found a link between having a light on at night and getting cancer). This shouldn’t be too surprising. So if you expose yourself to enough light at night that it keeps you from getting a good long sleep, it might adversely affect your health. But if having a light _helps_ you get a good night’s sleep, then you’re probably not hurting your circadian rhythm too much. My guess is that the benefits of having a solid 8 hours of sleep outweigh any risks associated with sleeping with a light on. However, it’s also possible that you’re sleeping later because the light causes you to have more fitful, less restful sleep at night and as a result you’re body just isn’t ready to wake up at your normal time. It seems to me that buying some black felt at Walmart/Joanne Fabric to drape over your windows to black out your room would be a much more effective solution. ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [October 12, 2012, 3:46pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/16 "2012-10-12T15:46:12Z")
Man, that moon up in the sky at night must have been slaughtering our ancestors by the millions. If only there was some way we could adapt to that over multiple generations. ---
**Author:** ![wheresmymind](https://avatars.discourse-cdn.com/v4/letter/w/91b2a8/32.png) [@wheresmymind](https://boards.straightdope.com/u/wheresmymind)\ **Post date:** [October 12, 2012, 3:54pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/17 "2012-10-12T15:54:11Z")
> [@engineer\_comp\_geek](#): > > Depends on the type of bulb. Old fashioned incandescent bulbs put out a very tiny amount but it’s nowhere near enough to worry about for health effects. CFL bulbs put out a bit more. Supposedly CFL bulbs also don’t put out enough to worry about, but a study done last summer found higher than expected levels of UV from every CFL bulb they tested, apparently due to cracks in the bulb’s phosphor coating. The articles I read about it made a big deal about significantly higher UV levels without actually saying what the levels were, so it’s hard for me to tell if there’s anything worth worrying about or if it’s a bit of typical journalist over-sensationalism. Yeah, I find that when the popular press reports on scientific studies, they often replace “statistically significant” (well within the error range of our instruments, or with some arbitrarily small p-value) with the everyday definition of significant (a considerable amount that will matter in practice). So even if they found levels that were only 1/1000th higher, if their results were statistically significant the press would likely report that as being a meaningful amount. ---
**Author:** ![Szlater](https://avatars.discourse-cdn.com/v4/letter/s/90ced4/32.png) [@Szlater](https://boards.straightdope.com/u/Szlater)\ **Post date:** [October 12, 2012, 4:00pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/18 "2012-10-12T16:00:35Z")
> [@engineer\_comp\_geek](#): > > Depends on the type of bulb. Old fashioned incandescent bulbs put out a very tiny amount but it’s nowhere near enough to worry about for health effects. CFL bulbs put out a bit more. Supposedly CFL bulbs also don’t put out enough to worry about, but a study done last summer found higher than expected levels of UV from every CFL bulb they tested, apparently due to cracks in the bulb’s phosphor coating. The articles I read about it made a big deal about significantly higher UV levels without actually saying what the levels were, so it’s hard for me to tell if there’s anything worth worrying about or if it’s a bit of typical journalist over-sensationalism. I was actually responding to the suggestion of using a theatre opening spotlight. Those are usually arc lights, aren’t they? Don’t arc light use a similar technique to generate light that spot welding does(arcing current between carbon terminals), thereby putting out huge amounts of UV? ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 12, 2012, 4:11pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/19 "2012-10-12T16:11:03Z")
> [@Szlater](#): > > I was actually responding to the suggestion of using a theatre opening spotlight. Those are usually arc lights, aren’t they? > > Don’t arc light use a similar technique to generate light that spot welding does(arcing current between carbon terminals), thereby putting out huge amounts of UV? Yes. Well, depending on what you call spot welding. It’s what an arc welder does. It produces a lot of IR also. It’s also noisy and smelly, and the carbon rods are consumed making it expensive. I didn’t realize the OP was using an arc lamp for a night light. Yes, I know that’s not what you meant. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 12, 2012, 5:00pm UTC](https://boards.straightdope.com/t/sleeping-with-light-on-cancer-risk/637512/20 "2012-10-12T17:00:52Z")
> [@Szlater](#): > > I was actually responding to the suggestion of using a theatre opening spotlight. Those are usually arc lights, aren’t they? > > Don’t arc light use a similar technique to generate light that spot welding does(arcing current between carbon terminals), thereby putting out huge amounts of UV? No theater uses Carbon arc lights anymore. They are all [High-Pressure Xenon.](http://en.wikipedia.org/wiki/Xenon_arc_lamp) Still, they emit copious amounts of UV (indeed, they are the primary UV source for IC lithography).