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If you shine a bright enough white light on a red object, will the object turn white or stay red? Please assume the object is not capable of specular reflection.

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Perception and reality are two different things. A red object is a red object. Even in darkness, the conditions that make it red are still there.

An overexposed red object takes into account the dynamic range of the sensor that was used to image it.

Exposure determines how much energy falls on the imaging sensor per unit of time.

Imaging sensors produce a signal that is proportional to exposure.

But, imaging sensors are finite elements. They cannot keep producing an infinite value for an infinite amount of exposure.

Therefore, inevitably, practical imaging sensors have a linear part in their response where proportional amounts of exposure produce proportional amounts of output but also a "plateau" part where the sensor is now fully saturated and no matter how much exposure is increased, the output remains the same.

Let's look at this sensor for a minute. Photographic film is composed of little crystals that produce an "optical density" when they are exposed to light. The higher the exposure, the more crystals are "activated", the more "optical density" is created. Once a crystal is "activated" it is taken out of action. It cannot be "re-activated" to produce more "optical density". Therefore, a given film emulsion, cannot keep increasing its optical density with exposure. At some point it "runs out" of crystals. Similar phenomena occur in photomultipliers and charge coupled devices (CCD) and limit the outputs of the sensors versus exposure.

Therefore, if you image a red object within the capabilities of the sensor, you will still see it as red.

If you image the object beyond the capabilities of the sensor, it might will appear white, because the exposure to light energy is so big that it has saturated all three channels (R,G,B) of the imaging sensor.

An object that appears white in a photograph, is not necessarily white in reality.

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When an object is Red, we mean that it only reflects the portion of the electromagnetic spectrum representing this color, about 650nm.

White light falling onto objects

For a red object, we generally consider that only the color red is reflected, like the XKCD-like diagram below.

XKCD red

Source:

EDIT:

This is a wavelength-intensity graph for various colored objects (anodised aluminum to be exact). The intensity is maximum for the wavelength associated with the color we see, but it still can reflect other colors, although at a much lower intensity as well.

Wavelength-Intesity Graph for Nanoporous alumina

Source:

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Well I just tried looking head-on at a 250 W infrared reflector bulb through a red filter and the brightest light looked yellowish white, turning green as my eye adapted. I guess the sensitivity of the different type color receptors overlap enough spectrally such that they can simultaneously saturate from just red-wavelength light, or the filter was not too selective. It would be unethical to try with a brighter source...

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