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Question DetailsAsked on 1/22/2018

Bedroom dark nothings visible no light able to come in suddenly the room lightens up & everything's visible,why

Something is causing my pitch black bedroom nothing inside is visible ,to lighten up at night to where items inside the room are easily visible what is it. There is no light able to come in any cracks or windows

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1 Answer


Assume you are not talking about just your eyes adjusting to the dark - it looking dark when you walk in from a lit hall or other room but looks lighter when you wake up or sit for awhile in the dark because your eyes have become night-adjusted. If that is the case, if you walk into the dark room and stand or sit down with eyes closed for a few minutes, then open them - you will see the same effect. That is just your eyes adjusting to the lower light level - so called "night vision", which happens with humans just like with dogs and cats - theirs is just much better tuned to low light conditions. If this is the case, same would be true in some other rooms (to varying degrees depending on what low-level sources of light they have.)

Otherwise, if it is actually getting lighter inside or there is a low level of light - hold something up to form a shadow (if that bright), and track back to where the light source is that way (light would be coming from the opposite direction from where the shadow appears). If very dull light may need to hold up a blanket or such to create a noticeable shadow zone. Could be a window shade or underdoor gap or even old- open "skeleton key" type keyhole or such which looks dark when room is lit but actually is letting some visible amount of light through which is noticeable only when room is dark. In very old houses with plank or panelling walls but without wall insulation sometimes light will seep through gaps between them into an adjacent room. In above cases, see if it goes away if you turn off all lights in adjacent rooms. If overlying room has open-gap wood flooring without plywood sheathing, can even sometimes shine through subfloor from above and out around ceiling light fixtures a bit.

Could also be a TV or computer monitor which is on a power-saving mode - some do not turn all the way off but instead stay on at lower power so they are "instant-on"- like when my HP monitor is on power-saving mode but not actually powered off it actually puts out a very faint illumination visible on the desk for a couple of feet when the room is totally dark. Or just a power switch which glows so you can find it in the dark.

Also - if an older cathode ray tube monitor or TV or projection TV, they commonly have a phosphor coating on the screen which will glow greenish in the dark for some minutes (as many as 10-20 minutes in some cases) after the device is turned off. Flourescent lights ("old " tube flourescents last much longer than CFL's) will continue to glow for a few minutes to sometimes as much as 10 or so after they are turned off, gradually fading to nothing as the gas in them deionizes after the energizing power is turned off.

Another possibility - computer monitor which goes "black" when computer is shut off or goes to sleep because there is no video signal coming in, but the monitor itself was not turned off so the LED backlighting is still active, so may produce a faint glow from the screen.

And of course, look around for any clock radio, plug-in alarm, night light, thermostat, fish tank, cell phone, plug strip, uninterruptible power supply, device or battery charger, "princess" type landline phone with nightlight built in, etc which may not show directly but may put off a small amount of light.

Stuffed animal or toy which glows - or glow-in-dark childs blanket or comforter.

Also glow from a computer mouse with laser movement tracking which is glowing because the computer is asleep, not off - usually glows red in that case though I have seen blue and green also.

Rare one but I tracked this down once for a person who needed a dead dark room to sleep well and worked night shift, so she slept in the day - a furnace return duct in the ceiling was disconnected so a diffuse light was coming through from the attic daylight through the grill. Ditto to possible light coming through a register or grill connected to an adjacent room which has the light on - possibly not directly visible behind furniture or such so you are just getting a diffuse glow.

Even rarer - there are a very few phosphorescent house plants which put off a slight glow in the dark - but I have never heard of one which can illuminate a room enough to see.

Is there a chance this was a teenager's or kid's room at one time and they put phosphorescent stars or paint on the walls or ceiling ? This will glow for from a few hours to, with the highest quality materials, as much as 8-12 hours after being exposed to bright room light or sunlight for about as much time during the day. Ditto for phosphorescent switch plates - there are even lighted switch plates which put out a diffuse weak glow to let people find them in the dark.

Ditto to some table lamps which have a weak light light built into the base to provide a bit of illumination to let people find them when they are off in the night - some glow at the base, some at the switch only.

Ran into this once - phosphorescent window shades, designed to act like a weak night light.

A painted-over window which is letting a dull glow through the paint.

If in a real old house in poor condition with some mold or fungal deterioration, some of them (mostly funguses) glow in the dark - but if you have enough to illuminate the room at all you have a SERIOUS water problem.

If a sporadic thing, probably car headlights or a neighbor's yard security light coming on or flashing past your house, getting in through some opening or through window shades or blinds - or maybe coming in through an adjoining room or bathroom unshaded window and then fainly illuminating your bedroom through a vent or transom window in adjoining door or through gap under the door.

If this list does not track it down, I guess time to call Ghost Busters. Not seriously.

Answered 2 years ago by LCD

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