Translation:Can I turn on the light?
Can't use could in combination with I, because then the meaning of the sentence changes to if you are able to instead if you are allowed. 可以開燈嗎？=can the light be turned on, or could somebody turn on the light or, is it ok i turn on the light? Could i turn on the light, to me sounds more like 我會開燈嗎 which is a bit of a weird question to ask in most situations.
The provided English translation is incorrect. It should be "Can the light be turned on?" because the Chinese sentence does not make a reference to who can turn the light on - it could be spoken to someone else asking them if they can turn on the light as well.
"Can I turn on the light?" requires the sentence to be 我可以开灯吗?