# Optical System on NextSeq 500/550

* Light-emitting diode (LEDs) are used for excitation on the NextSeq 500/550, although laser diodes are still present for auto-focusing purposes.
* Six cameras are used for capturing signal, and these are housed in independent imaging modules, which also contain the laser diode.
* For additional information on the laser for EH\&S (Environmental Health and Safety) purposes, review the [Safety Compliance Guide](https://support.illumina.com/content/dam/illumina-support/documents/documentation/system_documentation/nextseq/nextseq-500-550-system-safety-compliance-guide-15046564-03.pdf).

  ![](/files/C79G152efbGWbqru63F0)

For further information on swaths, tiles, cameras, and lanes, search for Knowledge Base article **Chemistry and Imaging on NextSeq 500/550.**\
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| *For any feedback or questions regarding this article (Illumina Knowledge Article #2076), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000002076%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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