When a candle is extinguished, its wick can still emit smoke that can be mistaken for a flame. This smoke can reflect ambient light, giving the impression that the candle is still lit.
When you look at a bright light source, like the flame of a candle, your visual cells called photoreceptors become highly active. Their nerve signals persist for a few moments even after you look away or the flame goes out. As a result, your brain still believes it perceives a faint presence of light where the flame was, creating the illusion that the candle remains slightly lit for a moment. This effect is called retinal persistence, and it is the exact same mechanism that explains why you continue to see a bulb or a bright screen for a few seconds after closing your eyes.
When the flame is extinguished, the warm wax and the wick continue to reflect and diffuse the light present in the room. Our eyes perceive this faint luminosity and interpret the candle as still slightly illuminated. This phenomenon depends on the texture and color of the candle: a light or shiny wax will diffuse the surrounding light more, enhancing the illusion. This also occurs more easily when the ambient light is dimmed, as even the slightest reflection becomes very noticeable. The brain is then deceived by this subtle yet sufficient perception, and sometimes concludes a bit too quickly that the candle remains lit.
Our eyes are not the only ones responsible when we fall into the trap of illusions: it mainly happens at the level of the brain! The brain does not just "passively receive" what the eyes send it: it interprets, reconstructs, and constantly completes the visual information received. Sometimes, it fills in the gaps with expectations or previous memories; in short, it improvises a bit to buy time (smart, but it can cause illusions!). As a result, you can easily believe that an extinguished candle is still lit, simply because the brain anticipated the flame or activated the mental image of a lit candle, deceived by retinal persistence or an image already stored in memory. These little mental shortcuts clearly show that when it comes to vision, it's not always what you see that matters, but what your brain has decided you should see.
The light intensity around you can create or enhance illusions, making an extinguished candle confusing to perceive. The darker the room, the more ambient light or subtle reflections easily deceive your gaze, giving the impression that the wick is still lit. Distance also clearly plays a role: the farther away you observe the candle, the more your brain invents details to fill in what it cannot precisely distinguish. Finally, a slight draft or subtle movements in your environment can sometimes alter perception by creating fleeting light variations, strangely resembling a flickering flame in motion.
Some optical illusions exploit brain mechanisms similar to those involved in the extinguished candle illusion. For example, the Troxler illusion reveals that fixed images placed at the periphery of the visual field can gradually disappear, demonstrating how malleable our perception can be.
Leonardo da Vinci was one of the first scientists to observe retinal persistence by describing how the eye can retain a light image for a few fractions of a second after its actual disappearance, paving the way for several modern optical inventions.
In the dark, our brain is particularly sensitive to the illusion of residual light. This is why we can see the glow of a candle, even when it is extinguished, for a few moments as its luminous image is still being processed by our brain.
The persistence of vision, responsible for many optical illusions including that of a extinguished candle that still appears to glow, also enables the operation of cinema and television screens, where our brain perceives a rapid succession of still images as continuous motion.
Our brain constructs a coherent interpretation of the visible world based on visual cues captured by our eyes. Thus, it sometimes tends to temporarily maintain the previous perception when visual information changes abruptly.
Sure! Here is the translation: "Yes. A low ambient light enhances the appearance of this illusion because it reduces the overall contrast, making the persistence of the flame more perceptible to the eyes."
Generally, retinal persistence lasts between 50 and 200 milliseconds, but this duration can vary depending on brightness, visual contrast, and individual sensitivity.
Yes, similar phenomena occur with bright lights that are suddenly turned off (lamps, screens, etc.), where the eye momentarily continues to perceive the extinguished light due to retinal persistence.
This phenomenon is related to retinal persistence: the bright image remains briefly imprinted on the retina, giving the impression that the flame is still present even though it has just gone out.
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