EKG/ECG No green light, but Heart Rate monitor has it.

lulumink

macrumors regular
Original poster
Sep 20, 2012
136
23
Every health lovers, have you noticed that when Watch is doing a ECG graph, it doesn't emit that green light. It can still be able to do detect my heart rate. However, if you use the heart rate monitor app only, it always emits that green light. I am just curious, why ECG doesn't use the green light. Does anyone know the reason behind this?
 

rattler

macrumors regular
Jul 18, 2011
126
22
The EKG sensors are able to detect the electrical rhythm of your heart, and thus they can measure your BPM without needing to activate the green LEDs.
 
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lulumink

macrumors regular
Original poster
Sep 20, 2012
136
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The EKG sensors are able to detect the electrical rhythm of your heart, and thus they can measure your BPM without needing to activate the green LEDs.
Thanks. That's what I figured. It needs to be connected by two points in order for this to work without having the LED light emitting.
- - Post merged: - -

If you place a finger on the crown, it'll also use the electrical sensors in the HR app :)
I tried, it doesn't really turn the LED off. It continues to shine the green light even if you put your finger on the crown.
 

Significant1

macrumors 6502a
Dec 20, 2014
796
253
I tried, it doesn't really turn the LED off. It continues to shine the green light even if you put your finger on the crown.
Because it can use both methods and toggle between them. But determining HR is not instant. You only see HR update every 5s using LED and the first measurement take even longer. So it will keep measuring using LEDs and fall back on that method, when you let go of the crown.

ECG can only be measured using electrodes, so no point having the LEDs running.

Read here how Apple Watch measure Heart Rate
 

lulumink

macrumors regular
Original poster
Sep 20, 2012
136
23
- - Post merged: - -

Because it can use both methods and toggle between them. But determining HR is not instant. You only see HR update every 5s using LED and the first measurement take even longer. So it will keep measuring using LEDs and fall back on that method, when you let go of the crown.

ECG can only be measured using electrodes, so no point having the LEDs running.

Read here how Apple Watch measure Heart Rate
Thanks for the article, that helps lot to clarify the problem.

However, in the article of Apple, it says the following:

To use the electrical heart sensor to measure your heart rate, open the Heart Rate app and place your finger on the Digital Crown. You will get a faster reading with higher fidelity — getting a measurement every second instead of every 5 seconds.

This doesn't work on my Watch Series 5. Heart Rate app ALWAYS lights up the green LED, even if I place my finger on the crown. I can't force the app to use electrical heart sensor. Only the ECG app automatically uses the electrical method without firing up the green LED.

So it looks like Apple Watch is using THREE methods to measure heart rate.

1. Infrared
2. Green LED
3. Electrodes

I'm just curious to know as why wouldn't Apple just ditch the green LED if the Infrared seems to be sufficient for the Workout app to measure HR? In the article, it says Infrared only measures in the background when the Watch is not active. I'm guessing that Green LED is simply stronger for reading situation such as workout due to sweat or movement. It's just my thought.

Any thoughts on this?
 
Last edited:

Significant1

macrumors 6502a
Dec 20, 2014
796
253
- - Post merged: - -

This doesn't work on my Watch Series 5. Heart Rate app ALWAYS lights up the green LED, even if I place my finger on the crown. I can't force the app to use electrical heart sensor. Only the ECG app automatically uses the electrical method without firing up the green LED.
Have you checked how often the puls updates? It doesn't have to turn off the green LED in Pulse when using electrical method. Read my post again. It can have both methods running and toggle between them instantly depending on whether you are touching the crown.

I'm just curious to know as why wouldn't Apple just ditch the green LED if the Infrared seems to be sufficient for the Workout app to measure HR? In the article, it says Infrared only measures in the background when the Watch is not active. I'm guessing that Green LED is simply stronger for reading situation such as workout due to sweat or movement. It's just my thought.

Any thoughts on this?
It uses the green LEDs for workout, not infrared. So if they had to ditch anything, it should be the infrared LEDs, since the green can do all puls related at lower power. Infrared/red however can measure Pulse Ox. But I am not aware that Apple measures that, though I think the hardware i capable of it. I have a garmin Vivosmart 4, which uses green LEDs 24/7 (Apple Watch only measure every 10 minutes) to measure HR and with very very good battery life. I has the option of measuring 4 hours of Pulse Ox at night (or on demand measurement). That uses infrared/leds, but impacts battery life noticeable and unless you are traveling in thin air or has Sleep apnea, there really is no reason to use battery on it.

So if Apple doesn't measure Pulse ox or anything else specific with infrared, I have no idea why they use for background measurements. Maybe it is more descreete at night. I know the green flickering from my garmin is noticeable visible in bed.
 

lulumink

macrumors regular
Original poster
Sep 20, 2012
136
23
Have you checked how often the puls updates? It doesn't have to turn off the green LED in Pulse when using electrical method. Read my post again. It can have both methods running and toggle between them instantly depending on whether you are touching the crown.


It uses the green LEDs for workout, not infrared. So if they had to ditch anything, it should be the infrared LEDs, since the green can do all puls related at lower power. Infrared/red however can measure Pulse Ox. But I am not aware that Apple measures that, though I think the hardware i capable of it. I have a garmin Vivosmart 4, which uses green LEDs 24/7 (Apple Watch only measure every 10 minutes) to measure HR and with very very good battery life. I has the option of measuring 4 hours of Pulse Ox at night (or on demand measurement). That uses infrared/leds, but impacts battery life noticeable and unless you are traveling in thin air or has Sleep apnea, there really is no reason to use battery on it.

So if Apple doesn't measure Pulse ox or anything else specific with infrared, I have no idea why they use for background measurements. Maybe it is more descreete at night. I know the green flickering from my garmin is noticeable visible in bed.
You are right on the first part about whether to touch the crown. It indeed updates faster after putting my finger on the crown.

About the second part, I am not sure whether infrared uses less battery to measure HR. If yes, Apple might decide to use it for measuring HR in 5-10min interval, since it's fairly frequent and might drain battery. This is just my assumption as I don't know which method uses the most battery. i can't think of anything other than saving power when using infrared method.
 
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