If you mean a strange light that appeared behind or around an electrical wall outlet, there are several possible explanations—some harmless, but some potentially dangerous.
What the light could be
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Electrical arcing: A loose wire, damaged receptacle, or poor connection can create a tiny electrical arc. It may look like a brief blue, white, or orange flash. Arcing can generate substantial heat and is a potential fire hazard.
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A loose connection behind the outlet: Wires that aren’t firmly secured can intermittently make and break contact, sometimes producing a visible glow, crackling, buzzing, or a burning smell.
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Light leaking through a gap: If the outlet box or wall plate has a small opening, light from another source—such as an LED, indicator light, or space behind the wall—can appear to come from the outlet.
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An illuminated outlet or device: Some receptacles have built-in indicator LEDs, and nearby USB chargers, smart plugs, surge protectors, or other electronics can produce light that is visible around the outlet.
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Reflection: A surprisingly small amount of light from a television, appliance, hallway, or another room can reflect off metal or plastic inside an outlet opening and make the source difficult to identify.
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Something inside the wall: Insects or other objects generally aren’t a normal explanation for a persistent electrical-looking glow, particularly if you also notice heat, smoke, odor, or sound.
The important distinction
If you actually saw sparking or a glowing point inside the receptacle, don’t treat it as merely a strange visual effect.
Warning signs include:
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Flickering or flashing from the outlet
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Crackling, buzzing, or popping
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A burning-plastic or electrical smell
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Discoloration or scorch marks
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A warm or hot outlet/cover plate
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A breaker that repeatedly trips
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Smoke
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Appliances connected to it behaving strangely
If any of these are happening, stop using the outlet and turn off the corresponding circuit breaker if you can do so safely. Don’t remove the outlet cover or touch exposed wiring. Have a qualified electrician inspect it.
If there is smoke, a strong burning smell, active sparking, or visible fire, move away from the area and contact emergency services/fire department rather than attempting to investigate the wiring yourself.
If you tell me what color the light was, whether it was steady or flickering, whether anything was plugged into the outlet, and exactly where you saw it (inside the socket, around the wall plate, or behind the outlet), I can narrow down what you likely saw.