# Where does the light go? **URL:** \ **Category:** Factual Questions\ **Created:** [August 1, 2009, 3:45am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954 "2009-08-01T03:45:55Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Stubbies](https://avatars.discourse-cdn.com/v4/letter/s/a9adbd/32.png) [@Stubbies](https://boards.straightdope.com/u/Stubbies)\ **Post date:** [August 1, 2009, 3:45am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/1 "2009-08-01T03:45:55Z")
We’ve all seen stars in the sky, light produced by suns millenia ago reaching us now, so the light produced has travelled somewhere. As a cinema projectionist I’ve been reflecting the light produced by 2.5kilowatt, 3.5kw, up to 6kw Xenon lamps off of movie screens for 24 years. Where does the light go, where has it gone? ---
**Author:** ![chacoguy](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@chacoguy](https://boards.straightdope.com/u/chacoguy)\ **Post date:** [August 1, 2009, 3:57am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/2 "2009-08-01T03:57:13Z")
It doesn’t 'go anywhere. It’s still right there in the form of heat; you just can’t see it anymore. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [August 1, 2009, 4:21am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/3 "2009-08-01T04:21:14Z")
Perhaps you’re thinking along the lines of [Olbers’ Paradox](http://en.wikipedia.org/wiki/Olbers%27_paradox)? The OP is rather short and unclear. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 1, 2009, 7:30am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/4 "2009-08-01T07:30:49Z")
Light that doesn’t hit anything just keeps on going. Light that does hit something either gets reflected and then keeps on going, or it gets absorbed and converted to heat. As an excellent rule of thumb, whenever the question is “where did the energy go?”, the answer is almost always “heat”. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [August 2, 2009, 3:57am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/5 "2009-08-02T03:57:20Z")
> [@Chronos](#): > > As an excellent rule of thumb, whenever the question is “where did the energy go?”, the answer is almost always “heat”. Which prompts the question, “Where did the heat go?” ---
**Author:** ![IAmNotSpartacus](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@IAmNotSpartacus](https://boards.straightdope.com/u/IAmNotSpartacus)\ **Post date:** [August 2, 2009, 5:37am UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/6 "2009-08-02T05:37:37Z")
> [@Fear\_Itself](#): > > Which prompts the question, “Where did the heat go?” Oh, it’s right there. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 2, 2009, 3:49pm UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/7 "2009-08-02T15:49:22Z")
And there, and over there, and that other place… ---
**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:** [August 3, 2009, 12:08pm UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/8 "2009-08-03T12:08:15Z")
> [@Fear\_Itself](#): > > Which prompts the question, “Where did the heat go?” It makes the object that absorbed it warmer. Example: earth is warmed by photons it absorbs from the sun. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [August 3, 2009, 1:50pm UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/9 "2009-08-03T13:50:54Z")
> [@Joe Frickin Friday](#): > > It makes the object that absorbed it warmer. Example: earth is warmed by photons it absorbs from the sun. Not entirely true. If the Earth retained the energy of all the photons that have reached it since it was formed 4.5 billion years ago, there would be nothing left but a smoking cinder. ---
**Author:** ![Precambrianmollusc](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/precambrianmollusc/32/63_2.png) [@Precambrianmollusc](https://boards.straightdope.com/u/Precambrianmollusc)\ **Post date:** [August 3, 2009, 2:21pm UTC](https://boards.straightdope.com/t/where-does-the-light-go/504954/10 "2009-08-03T14:21:49Z")
> [@Fear\_Itself](#): > > Not entirely true. If the Earth retained the energy of all the photons that have reached it since it was formed 4.5 billion years ago, there would be nothing left but a smoking cinder. The Earth looses a lot of the energy absorbed through infrared emission - wacky picture here. [http://asd-www.larc.nasa.gov/erbe/](http://asd-www.larc.nasa.gov/erbe/)