This is the only room that does it! If you just look at it you can see it get brighter and then it will get low. But this is after you turn the light off at the switch!
If the lamp is an LED lamp then the component inside that makes the light is a Light Emitting Diode. Without getting too deep into the electrical engineering and device physics.. The brightness of the light from an LED is related to the current flowing through it. It turns out that even a tiny amount of current flow can produce a subtle glow.
There are other components inside the LED lamp assembly called capacitors. They store electrical energy, somewhat like a battery. After the light switch is turned off there's no new energy flowing into the lamp but there is still some energy stored in the capacitors. That energy bleeds out slowly over time, providing a source for a tiny current in the LEDs, and giving a subtle glow for some minutes after the power is turned off.
If the lamp is fluorescent then you may be seeing after-glow. There are two likely sources. One is that the heated gas cloud inside the fluorescent tube continues to emit some light as long as it remains hot. That light is absorbed and then re-emitted by the phosphor coating on the inside of the tube glass. Another possible source is phosphorescence: those phosphors themselves may actually store a little bit of light energy and continue releasing it after the source has stopped.
These are becoming less common, but if the light switch happens to be an in-line dimmer or smart switch rather than an ordinary toggle switch, then it never is truly and fully "off." It always leaks just a little bit of power, which is drawn through the controlled light, and can cause the light to glow a little bit.
I will take a SWAG assuming nothing was changed electrically and say it has a dimmer (probably old style non LED type) and a LED light bulb. If so we have probably found your problem. To validate that is the problem on a temporary basis replace the LED light with a regular tungsten bulb and it should work properly. The solution get a different LED bulb or get the correct dimmer. I have seen this many times in the past, however if that does not solve it you probably have a bad switch.