The green light on the back of a smartwatch isn't just for show—find out the real reason behind it..
Anyone who wears a smartwatch has likely noticed the green light glowing on its back. Sometimes it stays on continuously, while at other times, it blinks at intervals. Seeing this, it is natural to wonder: why is there a green light on the back of the watch? Is it merely a design element, or is there specific technology at work?
In reality, this small green LED is linked to a crucial health-tracking feature of the smartwatch. Its primary function is to track your heart rate. To achieve this, an optical heart rate sensor is installed in the watch.
How does shining light on the skin reveal the heart rate?
When you wear the smartwatch, the sensor on the back shines green light onto the skin of your wrist. The sensor then measures how much of this light penetrates the skin and how much is reflected. The blood flowing through your body plays a key role here; when the heart beats, blood flow in the arteries surges and then subsides.
Consequently, the amount of light absorbed and reflected by the skin fluctuates. The smartwatch detects these minute changes and estimates your heart rate based on them. This entire process is known as PPG, or Photoplethysmography.
Why does the light sometimes glow continuously and sometimes blink?
If you have observed closely, the smartwatch's green light does not always operate in the same way. Sometimes it appears to glow steadily, while at other times, it flashes intermittently. This happens because the watch does not monitor heart rate in the same manner at all times. When continuous readings are required, the sensor may remain active for longer periods. For instance, during activities like walking, running, or working out, heart rates can change rapidly, prompting the watch to keep the sensor more active.
It is not just the green light at work
Smartwatches do not rely solely on green LEDs for health tracking. Many devices use specific sensors and types of light to measure metrics like blood oxygen (SpO2). Consequently, you might notice red or infrared light on the back of some smartwatches; not every light visible on the back of the watch serves the same purpose.
Does the green light harm the skin?
Now, the most important question: is this green light from the smartwatch harmful to the body or skin? Under normal usage, it typically causes no issues. It utilizes a low-power LED designed solely to assist the sensor in obtaining the necessary readings.
However, if you experience red marks, irritation, or any discomfort on your wrist after wearing the smartwatch for an extended period, it is best to remove the watch for a while. Often, the problem arises not from the light itself, but from wearing the watch continuously, sweat accumulation, or friction between the skin and the strap. So, the next time you see the green light flashing on the back of your smartwatch, there is no need to be concerned. It is neither a camera nor a spying feature; in fact, that small LED is a crucial component of the sensor technology that tracks health metrics like your heart rate.
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