Perception of light - a twist in the Bhaya Bherava sutta? In the Bhaya Bherava Sutta MN 4 translated by Bhikkhu Tannissaro this is stated as said by the Buddha. 

"There are some brahmans &amp; contemplatives, brahman, who have the perception of 'day' when it is night, and of 'night' when it is day. This, I tell you, is their being in a dwelling of delusion. As for me, I have the perception of 'day' when it is day, and of 'night' when it is night..."

However in the Capala Sutta A 7.58 and several other suttas the Buddha encourages meditators to develop the perception of light so that one "dwells by night as by day, and by day as by night."

How are we to reconcile these two statements?
There is a famous quote in the ancient Hindu tradition, "what's day for the worldly is night for the sage" - meaning, the worldly and the spiritual people have the diametrically opposite sets of values, what's considered good by one is considered bad by the other:


  What everyone considers night is wakefulness for the renunciate, and that in which all are wakefull is seen as night by the wise sage (BG 2.69).


The quote in Bhaya Bherava Sutta is a sarcastic joke on Buddha's part:


  There are some brahmanas-shramanas, oh brahman, who see the day in night, and night in day. This, I tell you, is their delusion. As for me, I see the day in day, and night in night.


What Buddha says here is that his teaching, the True Dharma, actually reconciles the two value systems and demonstrates how ethical and skillful action, sensual restraint, concentration, emotional intelligence, and wisdom - are the path to positive outcome for both the worldly as well as spiritually motivated people.

The quote in Capala Sutta A 7.58 is simply a casual reference to the serious meditator's preference to spend the nights in restful vigil, while spending days in meditation (SN 51.20):


  "And how does a monk dwell by night as by day, and by day as by night? There is the case where a monk at night develops the base of power endowed with concentration founded on desire &amp; the fabrications of exertion by means of the same modes &amp; signs &amp; themes that he uses by day, and by day he develops the base of power endowed with concentration founded on desire &amp; the fabrications of exertion by means of the same modes &amp; signs &amp; themes that he uses by night. This is how a monk dwells by night as by day, and by day as by night.