Usually, when we talk of light and dark, we mean the ability to see.
In a spiritual context, light refers to truth and dark to lies or obscuration.
Both concern clarity of seeing.
When I first saw without physical instrumentality (human eyes), I was experiencing the light of spiritual truth. The catalyst for that breakthrough (even though the breakthrough was short in duration) was one of love and selfless compassion for others. The only way to achieve the spiritual light of truth is through altruistic love. Self-concern (ego) is the blindfold of darkness that separates us. Spiritual awakening into the light of spiritual awareness is accomplished through love, humility, responsibility and a fearless confidence we know of as "faith."
It has been said that darkness cannot be dispelled by darkness. Only light can do that. Similarly, selfishness cannot solve selfishness. Hate cannot solve hate. Only love can do that.