Editing 1308: Christmas Lights

{{comic
| number    = 1308
| date      = December 25, 2013
| title     = Christmas Lights
| image     = christmas_lights.png
| titletext = Merry Christmas from xkcd!
}}

==Explanation==
Each light in this Christmas scene is represented by its {{w|electromagnetic spectrum}}, which shows in a graphical form how much energy is radiated by each wavelength of light.

These graphs plot the intensity of all visible radiation. Infrared and ultraviolet are partially plotted also, represented by black. It starts with longer wavelengths on the left ({{w|infrared}}), continues with {{w|visible light}} in the middle from red to blue, and ends with {{w|ultraviolet}} at the right. There are 4 distinct spectra in this comic:

In the center of the image, between [[Beret Guy]] and the couple, [[Cueball]] and [[Megan]], appears to be a light spectrum of a fire, notable because it emits a lot of energy in the infrared band (The left zone of the spectrum), emitted typically from hot sources, and in the red and orange zone. The spike toward the left hand side of the spectrum is likely the 4.3&nbsp;µm resonance wavelength of hot CO<sub>2</sub> characteristic of burning hydrocarbons; see {{w|Flame detection#Emission of radiation|Emission of radiation}}. Given the size of the spectrum and its positioning, this represents a fireplace at which the characters are warming themselves against the winter chill.

In the right of the comic appear some spectra arranged in the form of a Christmas tree. There are 3 different spectra in this "Christmas tree":

At the top appears a complicated spectrum, possibly that of a [http://led-brdf.wikispaces.com/Introduction+to+LEDs white LED], representing the tradition in some cultures of putting a star (or an angel, but still usually lit) at the top of the Christmas tree.

In the branches there are two simpler spectra repeated at various places, one with a peak in the green zone, representing a green light source, and other with a peak in the red zone, representing a red light source. Both of these represent the tradition of putting colorful decoration in the tree, in this case apparently red and green colored Christmas lights.

In [[835: Tree]] a similarly strange Christmas tree has been constructed using binary trees.

{| class="wikitable collapsible collapsed" style="width:100%"
! The solution to the light spectrum plots can be found here:
|-
|[[File:christmas lights real.png]]
|}

==Transcript==
:[Megan, Cueball, and Beret Guy sitting on the floor and a big spectrum with one peak is shown between them. On the right many smaller spectra are shown in a shape of a Christmas tree.]

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Christmas]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Beret Guy]]