There are multiple types of toggle switches available, and some even come with a light source (LED) embedded in the switch.

But, will the light on the toggle switch drain the battery? The light on the toggle switch will not drain the battery because it draws minimal current from the battery source. The light source is a Light Emitting Diode (LED) which is a very efficient light source, and requires low currents to operate.

There are some instances where the light might possibly drain the battery. This is only if the battery source has a smaller current capacity.I will discuss these possibilities later. 

Why the light on the toggle switch will not drain the battery

A toggle switch is a great addition to any project. 

It uses a rocker type contact mechanism which gives it a great tactile feel, and provides some satisfaction when turning a circuit on or off.

Some of the toggle switches even come embedded with a light (LED), that illuminates when the toggle switch is active. 

However, you might be concerned whether that light will drain your battery. To know for sure whether it will drain the battery or not we need to take a deeper look at the light source as well as the battery.

Deeper look at the light of the toggle switch

First let us take a deeper look at the light used to illuminate toggle switches. 

Light Emitting Diodes (LED) are the go to choice for providing illumination. 

It is a semiconductor light source that lights up when a current flows through it. They come in a range of sizes and colours.

They are slowly starting to replace conventional light sources (such as bulbs) as they require far less power to operate making them very efficient. 

Below is a simple circuit of an LED with a series resistor connected to a battery source. 

The voltage ratings for LED’s vary from one LED to the next.

But, one thing that is constant is the current draw. The current draw values tend to be between 20mA – 30mA. This is known as the maximum continuous current rating.

The closer the current is to the maximum current rating, the brighter the LED will be, and the lower the current the lower the brightness.

The series resistor is used to limit the current flow to the LED, and changes depending on the voltages used.

This current draw is for standard sized LED. 

The LEDs used in toggle switches (commonly known as indicator LEDs) are much smaller and draw far less current compared to a normal size LED. 

The current draw of these indicator LEDs can be as low as 100uA – 2mA. 

As you can see, the current is very minimal and will not drain a decent sized battery. 

Does type of  battery determine if the toggle switch light will drain it faster?

Lets, take a look at the battery. I just mentioned above that indicator LEDs draw minimal current and will not drain a decent sized battery. 

What does that mean? 

Batteries come in a variety of sizes, current capacities, discharge rates,voltages and chemical compositions.

To better understand if the indicator light will drain the battery you are using, you will need to know one thing about the battery you are using, its Capacity.

Capacity

The battery capacity is how much charge the battery is capable of storing. It is typically measured and denoted in Amp-hours or Milliamp-Hours.

To determine how long a battery will last we simply divide the Amp-hour rating by the current draw.

For example, some coin cell batteries are rated for 1Ah (1 amp-hour). So, if we assume the battery is connected to a standard sized LED (which draws 20 mA), the battery will be able to power it for 50 hours (1/0.02). 

We need to convert the 20mA into Amperes, so that is where we get the value of 0.02.

If we use the value of 2mA (standard current draw of light used in toggle switches), the battery will be able to power the light for 500 hours! 

Thats plenty!

So, when it comes to the question of will the light of the toggle switch drain your battery, it really depends on the capacity of your battery.

The higher the capacity of the battery the less affect the light of the toggle switch will have. However, if the toggle switch light is being powered by a low capacity battery, the chances of it draining the battery are higher.

While the current draw of the indicator light (LED) is minimal, if a battery with a very low capacity is used, it might possibly get drained.

However, if you are powering it with a standard sized battery, the toggle switch light will not drain the battery unless left on for days on end.

Why is a light used on the toggle switch?

So what is the main purpose the light is used on the toggle switch? The main reason for using the light is for indication purposes. 

It provides a visual cue that lets you know the state of the toggle switch. The light will illuminate when in the on position.

Having a visual representation of whether the toggle switch is the on position or not can benefit you in many ways. 

One of them being safety. You can easily tell what state the toggle switch is in by looking at the light. If you were supposed to switch off but forgot, a quick glimpse will give you an indication.

Other than safety, having a toggle switch that lights up is just cool! 

It can add some aesthetics to your project, and look awesome during the night time.

Can you get a toggle switch without a light?

You might have purchased a toggle switch with a light embedded in it without really wanting a light.

Are there toggle switches that do not have a light? Yes. The standard toggle switches come without any light embedded in them.

So, if you are looking for a toggle switch without any light, make sure to check the specifications on the product page of the website you are buying them from. 

Does the size of the battery matter if it will get drained by the toggle switch light?

As you saw earlier, the capacity of the battery is a major indication of whether it will get drained or not. 

The dimension of the battery does not necessarily have a proportional relationship with the capacity. What I mean by this is that, just because a battery is bigger, does not mean it has more capacity. 

Sometimes smaller batteries have more capacity than larger ones. It all comes down to the chemical composition.

So, when choosing a battery to power your project with a toggle switch that has a light, make sure to choose a battery that has a high capacity (amp-hours or milliamp-hours) to ensure it will not get drained. 

Do not select a battery based on its physical dimensions.

How to test how much current the light on the toggle switch is drawing–

Every toggle switch that has a light will draw different amounts of current. While the standard current draw is about 2mA, it can be handy to know the exact number so you can pick a battery accordingly.

To calculate the current draw of the toggle switch you have, you will need a multimeter capable of measuring current and place in series with the terminal that has the light connected to it as seen in the diagram below.

Make sure to only connect the switch when testing. Turn the switch on and check the multimeter reading to see how much current the light of the toggle switch is drawing. 

However, caution should be taken as you are directly connecting the positive terminal or the battery to the negative. So, keep it on for a very small amount of time.

What if the light of the toggle switch is draining the battery

What if you notice the toggle switch light is draining the battery but you still want to use the light?

Your best option here is to replace your current battery and purchase a battery with a higher capacity.

Can you disconnect the light from the toggle switch to drain less from the battery?

The most standard simple toggle switches that come embedded with a light have only 3 pins.

With this configuration, there is no way to disconnect the light (unless you open up the toggle switch and physically disconnect the LED circuit inside).

There are other types of toggle switches that have 5 pins. 

Here you have the option of using the embedded light or not. If you don’t want to use the light you skip wiring the LED+ and LED- pins.

Do you need to wire a series resistor for the toggle switch light?

The toggle switch has maximum current and voltage rating so the LED inside the toggle switch comes with its own series resistor to protect the LED from those maximum voltages and currents, so no external series resistor is required.

However, if you want to dim the light further, you can add a series resistor. 

How to wire up toggle switch that has a light

If you have a three pin toggle switch which has a light, and are a bit confused how to wire it, the video below explains it well.

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