In LED pixel systems, frame rate and refresh rate are often used interchangeably, but that can hide several different timing limits. It is more accurate to separate the source's incoming frame rate, the controller's outgoing pixel frame rate, and the pixel IC's PWM rate.
Understanding those three concepts makes it easier to diagnose choppy motion, frame overruns, latency, and camera flicker without attributing every problem to the same 'refresh rate' specification.
Defining the Terms
Frame rate, measured in frames per second (FPS), describes how often the control source generates or sends new image data. A frame represents a complete set of pixel values for a point in time, even though a networked lighting system may transport that frame as multiple Art-Net or sACN universes.
The controller's outgoing pixel frame rate is how often it can transmit a complete update to the configured pixel outputs. This is sometimes described as the display refresh rate. It is different from the pixel's PWM rate: PWM is generated inside the pixel driver IC to control LED brightness, and it is a separate specification that is especially important when the installation is filmed.
Frame Rate: The Content Side
Frame rate begins at the source, such as a media server, lighting console, or other Art-Net or sACN sender. The source transmits universe data at a chosen or variable update rate, and the controller assembles that data for its configured pixel outputs. Higher source frame rates can make fast motion more responsive, but only when the network and controller can sustain the same effective update rate.
Output Frame Rate: The Controller Side
The outgoing frame rate is constrained by the time required to process the incoming data and transmit each pixel frame. On each output, pixel data is normally serialized, so protocol speed, pixel count, channel count, and chipset reset or latch timing all matter. Outputs operate in parallel, which means adding pixels to one heavily loaded output can reduce the maximum outgoing rate even when other outputs are lightly loaded.
PixLite Mk3 devices report both incoming and outgoing frame rates in the Management Interface. For pixel types that support configurable speeds, a faster data rate can improve output frame rate, while a slower setting can improve signal integrity on difficult cable runs.
Where They Interact
The two frame rates meet at the controller. For smooth real-time playback, the controller needs enough output capacity to keep pace with the incoming data rate while maintaining acceptable latency.
If incoming frames arrive faster than the controller can finish processing and outputting the previous frame, an overrun occurs. The controller may have to delay or drop frames. PixLite Mk3 includes a 'Drop Frame on Overrun' option that can intentionally discard overrun frames to help maintain output synchronization.
If the controller's output capacity is higher than the incoming frame rate, it does not create extra motion detail. The most recent pixel state can simply remain displayed or be transmitted again; the visible motion is still limited by how often the source provides new content.
System scale also needs to be described carefully. Increasing the number of pixels on a single output generally increases its transmission time, but increasing the total installation size does not automatically reduce frame rate if the load is distributed across additional outputs or controllers.
Why This Matters in Real Projects
Smooth motion is not just about choosing a higher FPS. A higher source frame rate only helps when the controller can output updates at a comparable rate. If the incoming rate exceeds the achievable outgoing rate, the result can be dropped frames, tearing, added latency, or visibly stepped motion.
Camera flicker and rolling banding are a different issue. They are primarily affected by the pixel driver's PWM frequency and its interaction with the camera's shutter and frame rate, not by the controller's output frame rate alone. A low outgoing frame rate can make motion appear stepped on camera, but selecting pixels with a suitable PWM rate is the key specification for flicker-sensitive filming and broadcast work.
Large systems therefore require both good load distribution and realistic timing targets. More pixels on an output, a slower pixel protocol, or long timing requirements can lower the maximum outgoing frame rate, while additional controller outputs or additional controllers can restore capacity by sharing the load.
Interactive and real-time systems are sensitive to the complete latency path: content generation, network transport, controller processing, and pixel-output time. Incoming and outgoing frame rates should be checked together, while PWM rate should be evaluated separately when camera performance is important.
There is no single number that defines timing performance in a pixel system. Source frame rate determines how often new content is generated, outgoing pixel frame rate determines how quickly the controller can deliver those updates, and PWM rate determines how the pixel driver modulates LED brightness. Treating these as separate specifications makes it much easier to design for smooth motion, low latency, and reliable on-camera performance.