The amount of light produced in the core of a supernova is beyond comprehension, and equals 10^54 ergs. The Sun emits 4x10^33 ergs/sec, so in one blast a supernova produces more energy than the Sun does in about 3 x10^20 seconds or 10^13 years.

The luminosity of a supernova is this energy delivered over its roughly week maximum brightness period which leads to 10^54 ergs/600,000 seconds = 2 x 10^48 ergs/sec or 4 x 10^14 times the output of the Sun. This is why supernova regularly outshine entire galaxies of stars.

Now if such a supernova were 50 light years away, the flux would be L/(4 pi d^2) = 7 million ergs/sec/centimeters^2. The Sun at its distance from the earth of 150 million kilometers delivers a flux of energy of 4 x 10^33 ergs/sec divided by 4 pi d^2 = 2 million ergs/sec/centimeters^2.

So, in very round numbers such a nearby supernova would deliver 7 times more energy IN ALL FORMS than just the light energy we see from the Sun. But a large fraction of the supernova energy goes into accelerating particles, perhaps only 1 percent ends up in visible light, so although a supernova would be a bright, intense pinpoint of light in the sky, my guess is that it would be somewhere between a Full Moon and noon-day sunlight. It would certainly light up the night sky probably to the intensity of an overcast day. It would be quite an event to experience, and it would stay this way for several months before fading.

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