Why do light bulbs glow when switched off? 3 simple steps to fix this!

When using many types of light bulbs, many households face the situation that even though the power switch is turned off, the light bulb is still dimly lit, not completely off. Does this make family members feel confused, afraid, and do not know what is wrong? So why do the light bulbs still glow when switched off? You should immediately refer to the specific analysis through the article below to understand this, thereby proactively fixing the best.

What Types Of Bulb Can Glow After Switched Off?

Lighting technology is changing day by day, manufacturers are constantly offering new products with high lighting efficiency and features, modern technology. There are many different types of light bulbs on the market.

Sometimes electrical appliances, including light bulbs, can behave in unexpected ways. They may flash, or turn off and on again. This will really make you and your family feel uncomfortable. Some ideas or people can joke that it is the influence of some dark force. But science says that’s not the case and everything has a cause.

LEDs, CFLs (compact fluorescent lamps), and incandescent bulbs have been observed to emit dim light, to varying degrees. Mainly due to the different components inside the bulb.

Bulbs vary in quality, so poor-quality bulbs may glow, flicker, or buzz when turned off. You may also find that the problem is with the circuit, not the light bulb. Some light switches will release electrical residue even when the switch is off.

The Main Causes Of Glowing

Electrical problems are one of the most common problems today with many different types of failures, typically the phenomenon of light bulbs that are still glowing or dim even when the power is turned off. However, if you want to fix any problem, you also need to understand the cause, thereby correcting it properly, bringing high efficiency. Do most effectively and safely not arbitrarily intervene because it can lead to more serious consequences. Here are a few of the main reasons we found.

Main Causes Of Glowing
Main Causes Of Glowing

#1. Extra equipment

Some switches still run a small amount of electricity through the bulbs even when they are off such as timers, motion sensors… Consider, it could be that your switches have a problem. one of those features. Classic incandescent bulbs won’t light if only a small amount of electricity is flowing through them so you’ll never notice this current, but LEDs are more efficient and only use a low voltage source, due to there it will likely glow dimly.

#2. Impact temperature

This happens with filament bulbs. The filament of an incandescent light bulb emits light. When you disconnect the power to the bulb, the filament takes some time to begin to cool down. So it continues to glow while the filament is still quite hot for a few seconds and turns off completely when the heat is gone.

#3. Vaporization inside the light bulb

Fluorescent light bulbs are the most common place where this phenomenon occurs. The interaction of mercury and phosphorus inside the fluorescent tubes sometime after the light goes out produces a brightener.

#4. Wiring wrong

This is the most likely you will encounter. During the wiring to the switch, you may have made the wrong wire. Normally, when connecting the hot wire to the switch, it will be mistakenly connected to the coil wire. If incandescent bulbs are used, they won’t light up, however, LEDs only use low voltage, so a dim glow occurs when the switch is off. In this case, you just need to reconnect the circuit to the standard to fix it.

Why Do CFL Bulbs Glow When Turned Off?

Turn it on for 2-3 hours and then turn it off. A few minutes later the CFL bulb glowed on its own without any source. This light barely stays on for 2 seconds, turns off, and then flashes again after a certain amount of time.

The vaporization effect is demonstrated in operating CFLs due to the interaction of mercury vapor and the phosphor layer inside the tube.

A little explanation for this phenomenon: Mercury vapor becomes ionized when the current begins to flow through the tube after the switch is turned on. In the non-ionized state, the electrons emit energy in the form of UV radiation and excite the phosphor coating. This interaction then emits photons of visible light. When the switch is off, it takes a few seconds for the electrons to stop releasing energy. During these few seconds, the ultraviolet radiation of the ionized mercury still reacts weakly with the phosphorus, emitting a residual photon of visible white light.

Or it could be a leak in the switch. There is a very small current flowing through the filter capacitor after the input rectifier of the CFL electronic ballast circuit. Diac triggers a circuit to ignite the lamp after the capacitor voltage reaches a certain voltage. That’s why you see lights trying to ignite after a long charge period and glowing.

Why Do LED Lights Keep Glowing After Switching Off?

This is a fairly common problem (especially with cheap, low-quality LEDs). The good part is that you can fix the problem easily. LED bulbs, compared to halogen or incandescent bulbs, have a much higher resistance than the built-in power supply. The LED also continues to glow faintly after the power is turned off. Excess electricity will still cause the shine to last from a few seconds to several minutes. A capacitor can supply an LED with enough electricity to light up for a short time. You can limit this effect by using a power supply with a smaller filter capacitor.

LED bulbs vary greatly in quality. Low-quality LEDs may glow, vibrate or blink even when turned off.

Swap fancy switches for regular switches to prevent dripping of current, or modify the wiring to have both hot and neutral wires in the switch. Replacing quality switches or bulbs from reputable brands will be more secure.

***Refer to more: 6 Common Problems With LED Lighting & How To Fix Them

How to fix it so that the light bulbs no longer glow when switched off?

How to fix it so that the light bulbs no longer glow when switched off?
How to fix it so that the light bulbs no longer glow when switched off?

The solution for this case is to replace the bulb with another suitable large capacity or install a resistor in parallel with the bulb.

Tips: When these problems occur, you should not carry out the repair yourself because if you do not understand the power source thoroughly, the circuit will be prone to accidents, and the repair will not be effective. This can cause fire and explosion and loss of material and life. Therefore, you should carefully refer to the article so that we can assist you to solve the problem most effectively and safely.

If you still cannot find the cause yourself, for more peace of mind, you can directly contact the electrical repair service of reputable companies or skilled workers.

Find out the exact reason why the light bulb is still dim when the power is turned off so that you can have the most effective remedy for you.

There are many ways to fix the phenomenon of turning off the switch and the light still on and blinking. To find a quick fix, follow these steps:

Step 1: Check the bulb

When checking, the light bulb is not damaged, but there is still a flickering phenomenon, the light bulb still does not light. Then you need to continue to perform the next test steps.

Step 2: Check the light switch

For LED bulbs that are installed outside, we should check the light breaker. Check if the starter is black or broken or is still lit. If the starter is no longer lit or has turned black, you should remove the starter and replace it with a new one. For starters that are fixed inside to protect the trough, you should turn counter-clockwise to remove this cover.

Step 3: Check the ballast

It is also necessary to check the ballast to help you check the wiring connection. You should remove the lamp tray to disassemble the ballast to check most effectively. Then test the ballast in the lamp to try again. If the ball still flickers, blinks forever, it means the ballast is damaged. You should proceed to replace the new ballast to help the lamp overcome the flickering and light the bulb.


The above is a summary of information on the question of why the light bulbs glow when switched off? that we want to send to you. Hopefully, this article will help you know more about the causes and how to fix the lights when there is a problem. Take some time to read and reflect on them.