Question: I have so far only worked with WS2812 strips and understood, that the WS2813 have a backup data line. But how do I connect the first LED to my Arduino (acts as a controller)? 

Many tutorials said I should just wire the BI to V0, but doesn't this eliminate the backup functionality? So I thought about wiring both data pins to my data source? Is this a good idea?

Answer: 
No, not connecting the BIN doesn't eliminate the backup functionality. As for what to do with it, the official datasheet at <http://www.world-semi.com/DownLoadFile/117> doesn't say, so I won't speculate.

To show that the backup remains consider that the BIN of a WS2813 LED is connected to the DIN of the previous LED.
![Typical application circuit of WS2813B](https://i.imgur.com/ucVLOx2.png)

If the first LED is working, then it receives and shows the data on it's DIN and then forwards the next pixel data via DOUT to the DIN of the next LED in the chain. Note that the second LED will now receive it's data on both BIN (direct from the first LED's DIN) and on DIN (repeated by the first LED).

If the first LED is non-functional, then the next LED first sees the first pixels' data on it's BIN (and disregards it). It is then expecting data for itself on the DIN channel but receives none. Thus it goes into backup mode and uses the data that came in on the BIN channel direct from the DIN of the first LED.

Thus, DIN is the one that needs to be connected on the first LED.
The WS28xx series of LED drivers are (were?) made by [Worldsemi](http://www.world-semi.com/), but there does not appear to be a datasheet for the WS2813 available on the site (yet). It seems that another company, [Shenzen Normand Electronic Co](http://www.normandled.com/) may be the manufacturer. Maybe it is a copy or a clone... The [datasheet can be found here](http://www.normandled.com/upload/201605/WS2813%20LED%20Datasheet.pdf).

In any case, page 2 states that data at `BIN` and `DIN` are compared. `BIN` is used in the event `DIN` does not receive valid data. It is not well-written; here is the relevant section:

> 
> The BIN receives the data signal, and then compare the data with the DIN side after phagocytosis of 24bit data, if DIN do NOT receive the signal, then switching to BIN for receiving the input signal, which ensure that any the IC's damage does not affect the signal cascade transmission and make the BIN in state of receiving signal until restart after power-off.
> 
> 
> 

I'm amused by the inclusion of *phagocytosis*, a biological process whereby cells can "eat" large particles by engulfing them. I presume this is a bad translation that refers to the process of receiving and checking the 24-bit data packet common to the WS28xx family of LED drivers.

The main purpose of this is not to operate a second LED strip, but rather to allow a single contiguous strip to tolerate failed pixels.

[![WS2812 vs WS2813](https://i.stack.imgur.com/Vflcw.jpg)](https://i.stack.imgur.com/Vflcw.jpg)

*[Image from Elecrow.com](https://www.elecrow.com/blog/ws2813-vs-ws2812/)*

Essentially DIN is a primary data input and `BIN` is a backup, just as you described. The datasheet does not specify how `BIN` should be connected (or left disconnected) if the backup data function is not wanted.

Based on what I was able to find, it appears that you could easily connect data to both `DIN` and `BIN`, and if one of the driver ICs fails, it appears that `DO` will still pass whatever data was received at `BIN`.

If you prefer to not use this pin, you could connect it to ground as some suggest. You may want to test whether connecting `BIN` to ground causes any additional current to flow, should that be a concern in your project. It could be that it is best left floating (not connected) instead. Measure to be sure.