Terminology » dToF vs. iToF LiDAR: Key Differences and Use Cases

dToF vs. iToF LiDAR: Key Differences and Use Cases

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Introduction : There are two primary ways light is used to measure distance in LiDAR which include Direct Time of Flight (dToF) and Indirect Time of Flight (iToF).

While both technologies rely on the speed of light, they use very different physical principles to calculate the “time” component.

Direct Time of Flight (dToF) LiDAR

It is the most intuitive approach and is frequently used in long range applications like autonomous driving. It functions just like “stopwatch”.

The system fires a short, powerful pulse of laser light. At the exact microsecond the pulse leaves the emitter, a timer starts. When the light hits an object and reflects back, the sensor (usually a SPAD or SiPM) stops the timer.
Distance (D) or Range (R) can be measured as we know speed of light (c) and round trip time delay.

LiDAR Time of Flight Distance Formula

Benefits : dToF is exceptionally good at long ranges because it can distinguish a single pulse from background solar noise. It can also detect “multiple echoes”. For example, seeing a pedestrian through a glass window or through heavy rain.

Indirect Time of Flight (iToF) LiDAR

Instead of timing a single pulse, it measures the properties of a continuous wave of light. The iToF is the phase-shift method. This is common in consumer electronics, like smartphone face ID or indoor robotics.

The system emits a continuous, modulated wave of light (often a sine wave). Instead of a stopwatch, the sensor compares the phase of the outgoing wave with the phase of the reflected wave. The “shift” or delay between these waves tells the system how far the light traveled.
The distance is calculated based on the phase difference relative to the modulation frequency of the light.
benefits : iToF sensors can be built using standard CMOS processes (similar to camera chips), allowing for very high resolution (i.e. megapixel depth maps) at a lower cost for short to medium distances.

Indirect ToF LiDAR Distance Formula

Comparison between Direct Vs. Indirect Time of Flight (ToF) LiDAR

Feature	Direct ToF (dToF)	Indirect ToF (iToF)
Measurement method	Measures travel time of a discrete pulse to determine distance of target	Measures phase shift of a continuous wave to determine target distance and velocity.
Optimal range	Long range	Short to medium range
Outdoor performance	Excellent, high immunity to sunlight	Moderate, can be drowned out by the sun
Resolution	Lower spatial resolution (Point clouds).	High spatial resolution (Depth images).
Power consumption	Higher peak power, lower average power.	Lower peak power, higher average power.
Complexity	Requires high precision timers (TDCs).	Requires complex signal processing for phase.
Multi-echo detection	Can see through rain, fog or glass.	Struggles with multi path interference.
Typical use case	self driving cars, drones, surveying	Face-ID, indoor vacuum robots, AR/VR etc.

Summary

The choice between direct ToF Versus Indirect ToF LiDAR lies based on application or use case as follows.

Choose dToF if you are building an outdoor system that needs to see hundreds of meters away, such as a long range drone or an autonomous vehicle. It is rugged, handles solar noise well, and provides high speed data for safety critical decisions.
Choose iToF if you need high resolution 3D images for an indoor environment or close range interaction. It is perfect for gesture recognition, 3D room scanning or industrial robots working in controlled lighting.