Is it permissible to pray in the dark?

It is permissible to perform prayer in a dark place, and there is no harm in it. However, the belief that praying in a dark place has a special virtue or increased reward is an innovation with no basis. If turning off the lights makes the worshipper more devout and less distracted, then there is no problem with it. But the concern arises when some believe that prayer is not complete except in this manner, which then falls under the category of innovations (bid'ah). The determining factor in this regard is the intention and purpose of the doer. So, if someone prays alone in their home and turns off the lights to focus their heart without believing in any special virtue, then there is no harm in that.