The green light bulbs in the Apple Watch are nothing more than heart rate sensors that are useful when exercising. There are many functions in smartwatches, and one of them is a built-in heart rate monitor. It operates on the principle of photoplethysmography.
Why Apple Watch has green lights: how does it work
The watch can detect the volume of blood that passes through the wrist in a certain period of time. Blood, as we know, is visible to us in red, because it completely reflects the red color and absorbs the green with the same intensity. Therefore, with a large amount of incoming blood at the time when heart muscle contracts, the absorption rate increases, and at the time of blood outflow, respectively, it decreases.
You can use the iWatch to measure your heart rate. It is calculated using the following algorithm:
- Activating the diodes to examine the skin.
- Increasing the flickering frequency when the visibility is low.
- The sensors pick up the light reflected from the skin.
- The heart rate is calculated and the indicator is displayed on the screen.
In addition to the green light, the watch can use infrared radiation. The green LEDs are activated if the blood flow is not visible enough. LEDs are used up to a couple of hundred times per second, and their flickering is not perceptible to the human eye. Infrared LEDs are less accurate, but use considerably less energy.
Light-sensitive LEDs on the watch show the heart rate. In addition, if the blood flow can’t be seen clearly enough, the frequency of flashes and the intensity of the green light bulbs in the Apple Watch may temporarily increase.