Jupiter gets just 4% of the sunlight Earth does. Yet noon on its cloud tops is still ten times brighter than a well-lit room—and so glaring that telescope cameras have to fight not to overexpose it.
Because Jupiter orbits at roughly 5.2 astronomical units from the Sun, the inverse-square law reduces solar intensity by a factor of 27. Direct sunlight at Earth's distance delivers an illuminance of roughly 100,000 to 130,000 lux, which leaves Jupiter with around 4,000 to 5,000 lux hitting its upper atmosphere. Typical indoor office or living room lighting ranges from 300 to 500 lux, making Jupiter's cloud tops about as bright as an overcast afternoon on Earth.
Human eyes underestimate just how intense daylight is because the visual system perceives brightness logarithmically rather than linearly. A 96% drop in raw photon flux sounds like near-darkness, yet to a human observer floating above Jupiter's clouds, the scene would look like normal daytime. Even out at Pluto, nearly 40 AU from the Sun, midday sunlight is still around 80 lux—comparable to a hallway light and hundreds of times brighter than a full moon on Earth.
Two physical traits of Jupiter itself make capturing that light from Earth even easier. First, the planet is wrapped in reflective ammonia-ice clouds, giving it a geometric albedo of about 0.52—more than four times as reflective as Earth's Moon, which has an albedo of just 0.12 and is roughly as dark as worn asphalt. Second, Jupiter's equatorial diameter of 142,984 kilometers gives it a huge cross-section to intercept sunlight and an apparent disk spanning up to 50 arcseconds in the night sky, wide enough for backyard telescopes to resolve individual cloud belts and the Great Red Spot.
For telescope cameras, this surface brightness poses the opposite problem of faint deep-space nebulae. Amateur astrophotographers do not use long exposures to gather scarce light from Jupiter; instead, they record high-speed video at millisecond exposures—often 60 to 150 frames per second—to freeze the blurring motion of Earth's atmosphere before the planet saturates the sensor.