# 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). ![](https://761066130-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FGM9W2DuBTgEXv1ClCm8H%2Fuploads%2Fgit-blob-d6a0162b8d62429e5e2378139bd08fe172f0369b%2Fimage1.png?alt=media) 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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