Answer: Dieffenbachia likes medium light, so I think the dead spots on the leaves are sunburn. I'd move the plant. A good place would be in front of an east window, where it would get a little morning sun, then light but no direct sun for the rest of the day. The plant can adapt to lower light levels, like in a north window or in a bright room but away from the windows. It will tolerate brighter light, but full sun in a south window might be too much for it.
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