# What is the PhiX Control v3 Library and what is its function in Illumina Next Generation Sequencing

The PhiX Control v3 Library (commonly referred to as PhiX, [FC-110-3001](http://www.illumina.com/products/phix_control_v3.html)) is derived from the small, well-characterized bacteriophage genome, PhiX. It is a concentrated Illumina library (10 nM in 10 µl) that has an average size of 500 bp and consists of balanced base composition at \~45% GC and \~55% AT.

**Calibration Control**

The PhiX Control v3 Library can be sequenced alone and serves as a calibration control for:

* Cross talk matrix generation
* Phasing and prephasing calculations
* Examining the overall performance of Illumina sequencing platforms

For detailed information, see:

* [PhiX loading concentrations for validation runs on Illumina sequencing platforms](https://support.illumina.com/bulletins/2016/10/phix-loading-concentrations-for-validation-runs-on-illumina-sequencing-platforms.html)
* [How to set up the sample sheet for a PhiX validation run on the MiSeq system using Illumina Experiment Manager](https://support.illumina.com/bulletins/2016/03/how-to-set-up-the-sample-sheet-for-a-phix-validation-run-on-the-miseq-system-using-illumina-experiment-manager.html)
* [How to set up a PhiX validation run on the NextSeq 500/550 in manual mode](https://support.illumina.com/bulletins/2016/03/how-to-set-up-a-phix-validation-run-on-the-nextseq-in-standalone-mode.html)
* [How to set up a PhiX validation run on the NextSeq 500/550 system using BaseSpace Hub Prep tab](https://support.illumina.com/bulletins/2016/04/how-to-set-up-a-phix-validation-run-on-the-nextseq-system-using-.html)
* [How to set up a PhiX validation run on the NextSeq 1000/2000 sequencing platform](https://support.illumina.com/bulletins/2021/03/how-to-set-up-a-phix-validation-run-on-the-nextseq-1000-2000-seq.html)
* [How to set up a PhiX validation run on the NovaSeq 6000 sequencing platform](https://support.illumina.com/bulletins/2017/08/how-to-set-up-a-phix-validation-run-on-the-novaseq-sequencing-pl.html)
* [Local Run Manager: How to set up a PhiX validation run](https://support.illumina.com/bulletins/2017/01/local-run-manager--how-to-set-up-a-phix-validation-run.html)

**Run Quality Monitor**

Due to its balanced nucleotide composition, the PhiX Control v3 Library is also an ideal sequencing control (typically with ≥ 1% spike-in) for run quality monitoring; eg, cluster generation, sequencing, and alignment.

**Color Balancing**

For low diversity libraries, the PhiX Control v3 Library provides balanced fluorescent signals at each cycle to improve the overall run quality. For detailed information, see:

* [What is nucleotide diversity and why is it important?](https://support.illumina.com/bulletins/2016/07/what-is-nucleotide-diversity-and-why-is-it-important.html)

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #1545), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000001545%20-%20Library%20Preparation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |