Understanding the Difference Between Optical and Electrical Heart Rate Sensors

Heart rate monitoring is a standard feature in today’s tech which includes fitness bands, smartwatches, and professional health equipment. We see people using these devices to get info on their health, fitness progress, and overall well-being. Although heart rate tracking may appear simple, the tech which makes it happen is quite complex. We have mainly two types of heart rate sensors: optical heart rate sensors and electrical heart rate sensors.

Although we see the same outcome in which we measure heart rate from all of them, the methods they use to collect and present that data are very different. To understand how these sensors function, what they do well, and what is less so will help you see why some devices choose one over the other and some which use a combination of both.

What are optical heart rate sensors?

As blood flows, your heart in its pumping action varies the volume of that blood which passes through your capillaries.

Optical sensors typically consist of:

• A light source which is usually a green LED (at other times infrared or red lights).
• A photodiode which measures the light which returns from your skin.

As light goes into your skin, some of it is taken in by the blood and tissue and some is reflected back. Your heartbeat changes the blood flow which in turn changes the amount of light that is absorbed. By looking at these variations, the sensor determines your heart rate.

This method is an in and out procedure which has made it very easy to put into wearable devices, which is what made it so popular in consumer electronics.

What does an Electrical Heart Rate Sensor do?

Electrocardiography (ECG or EKG) is the principle used for electrical heart rate sensors. What they do is measure the very small electrical signals which the heart produces at each beat instead of tracking blood flow.

An ECG sensor uses electrodes applied to the skin. In clinical settings, we see these electrodes used at the chest, arms, or legs. In wearable devices what you have are smaller conductive surfaces which act as electrodes that detect the voltage changes from heart activity.

Every time the heart beats, it produces a unique electrical signature. Through this signal, ECG sensors analyze and in turn provide very accurate information not only of the heart rate but also that of the heart rhythm and the health of your heart.

In the hospital and in medical devices, ECG sensors are very much at home. On the other hand, for wearables we see more of optical sensors.

Between optical and electrical sensors.

Although of the two types which are aimed at tracking your heart rate, it is in the methods of data collection, accuracy, and what they are used for where we see the difference. To put it out there:

1. Way of Measurement.

• Optical sensors (PPG): Use luminescence to determine blood flow.
• Electrical sensors (ECG): Use electrophysiological sensors to detect electrical activity.

2. Performance Accuracy.

• Optical: Generally good for resting heart rate and moderate activity which can be impacted by motion, skin tone, tattoos, and placement.
• Electrical: More exact in fact for detecting irregular rhythms, also at times requires skin contact and in some cases multiple electrodes.

3. Position.

• Optical: Worn in wristbands, watches, or fitness trackers.
• Electrical: In chest straps, ECG machines, or advanced wearables with electrode pads.

4. Data which was given out.

• Optical: Primarily measures heart rate (bpm).
• Electrical: Provides a look at your heart rate and rhythm in detail which is great for spotting issues.

5. Handy.

• Optical: Continuous tracking with little to no input from the user.
• Electrical: More precise but not as easy for continuous use.

Why do we see so much of optical sensors in wearables.

In terms of what consumers are into, we see that which is the appeal of optical heart rate sensors in wearables is a play on convenience, size, and cost. Most people go for a watch they can wear all time without issue which is where optical sensors’ small size, low price, and ease of integration into design comes in.

For average users’ needs, optical sensors are enough to check out heart rate while at rest, how hard they are working out, or signs of when they are in recovery post workout. While we may see them put out at times, they are not for medical diagnosis, instead which is to give a general idea health wise.

In what way have Electrical Sensors become the standard in Medicine.

Electrical heart rate sensors may have a more complex design and placement which in turn means that they are more in your face, but what they lack in terms of ease they make up for in accuracy and reliability which is what healthcare needs. In hospitals we see use of ECG monitoring which is for detection of arrhythmia, post-op care, and in the evaluation of in-depth heart function.

In consumer products that include electronic sensors, we see that they usually require some action from the user. For example, some smartwatches will ask you to put a finger on the watch face to complete a circuit which in turn allows the device to take a short ECG.

This deliberate process highlights the difference: Optical sensors used for constant, carefree monitoring, on the other hand, electrical sensors which are used for precise, diagnostic-level measurements.

Strengths and Limitations of Optical Sensors

Strengths:

• Comfortable for long-term use.
• Non-invasive and inexpensive.
• Can report continuous data around the clock.

Limitations:

• In some cases may not be accurate during movement, which includes running and very active times.
• May be influenced by skin characteristics which include pigmentation, tattoos, or body hair.
• Less reliable in high-intensity workouts as compared to chest straps.

Strengths and Limitations of Electrical Sensors

Strengths:

• Highly accurate and reliable.
• Can also identify out-of-sync heart rhythms which optical devices may not.
• Standard in medical-grade monitoring.

Limitations:

• Less comfortable for long-term continuous use.
• Usually a deliberate placement and skin-to-skin contact.
• More pricey and larger in design.

When to Use Each Sensor

What you need depends on which type of heart rate sensor you choose.

Optical sensors do well if you are after convenience, all-day wear, and a wide range of your activities, sleep, and workouts to be tracked. They are for lifestyle and fitness monitoring.

Electrical sensors are a must in critical situations which include medical settings and detection of irregularities. Also, they are the choice of serious athletes which require precise results from intense training sessions.

Today we see that some devices which are very advanced combine optical sensors for regular use and electrical sensors for very precise measurements at times.

The Future of Heart Rate Sensing

As technology advances, both optical and electronic sensors are improving. In the field of optics, we are seeing better performance in regard to error correction for movement, and in the electronics field, we are seeing the sensors get smaller and into more consumer-oriented products.

Conclusion

Heart rate sensors may be simple to use; at first glance what is going on under the surface is very different. In terms of optics, we have sensors that use light to measure blood flow which is great for all-day wear. Then there are the electrical sensors which look at the heart’s actual electrical signals. They may be a bit more uncomfortable to wear but offer unsurpassed accuracy and the ability to analyze heart rhythm.

Both present different sets of pros and cons. Optical sensors do better in terms of convenience, electrical in terms of precision. We see which ones perform best in each aspect which is why some devices choose one over the other and others which use a combination of both. As we see wearables and medical tech grow and improve, we are seeing that line between what is monitored by light-based and electric methods is blurring, which in turn is giving the users greater access to very accurate info about their heart health.