Since ITER will be a full metallic wall machine, scattered photons from the strong emission in the divertor may distort the emission from the scrape-off layer (SOL). The influence of stray light for visible spectroscopy of H α and Be I emissions in ITER was investigated with a ray-tracing simulation. It was found that the stray light would be always more than one order of magnitude greater than the real signal intensity for H α emission from the SOL. For Be I emission, although the situation was better than the cases of H α measurement, the stray light could be much larger than the real signal from the SOL. In ITER, it will inevitably reduce the stray light somehow for visible spectroscopy. The effect of optical dumps embedded on first walls was investigated with the ray-tracing analysis.

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