Smartwatch : Why Is There a Green Light Under Your Smartwatch?

Smartwatch : Have you ever taken off your smartwatch and noticed a green light glowing underneath it? If you have, you may have wondered what it is actually doing there. The light can sometimes stay on for a while and then disappear. At other times, it may blink for just a few seconds.

There is a simple reason for it. The green light is part of the smartwatch’s heart rate monitoring system.

The light comes from small LEDs placed alongside optical sensors on the back of the watch. When the watch is sitting against your wrist, these LEDs shine green light onto your skin. The sensor then looks at how that light behaves as it reaches the tissue.

This is where your blood flow comes into the picture.

Every heartbeat changes the amount of blood moving through the small blood vessels near the skin. Those changes also affect how much light is absorbed and reflected. The smartwatch detects these tiny differences and uses them to work out your heart rate.

The technology behind this process is called photoplethysmography, or PPG.

You may notice the green light more often when you are walking, running or exercising. That is because your heart rate is changing during physical activity, so the watch may need to take readings more frequently. When continuous tracking is not necessary, the light may only come on occasionally.

The exact behavior can vary from one smartwatch to another. It can also depend on the settings and health features being used at the time.

And no, the green light is not the only light these watches can use.

Some smartwatches also have red or infrared LEDs. These are used for different types of measurements, including features related to blood oxygen levels. So, if you see different colored lights under a smartwatch, they may be working with different sensors for different purposes.

There is also no need to worry about the green light simply because it is shining directly onto your skin. The LEDs used for this purpose are low power and are designed for optical sensing during normal smartwatch use.

If your wrist becomes red or irritated after wearing the watch for hours, though, it is worth giving your skin a break. Sweat, friction, a tight strap or keeping the watch on continuously can sometimes cause irritation.

So, the next time that little green light appears under your smartwatch, there is no mystery behind it. It is one of the sensors helping the watch keep an eye on your heart rate while you go about your day.