Guides:Lighthouse back-facing hits

From VRChat Wiki
Revision as of 13:42, 7 April 2026 by Hackebein (talk | contribs) (Is lighthouse EOL?)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
V · ECommunity-written content
The following was created by the community. It may contain material not directly endorsed by the VRChat team. To learn more, consider reading Contributing to the VRChat Wiki.

Back-facing hits are a diagnostic metric in SteamVR that applies to Lighthouse-based tracking systems. The metric counts the number of infrared light signals received by a tracker's sensors from an indirect direction, typically caused by reflections in the play space. A high number of back-facing hits indicates that the tracking environment may have reflective surfaces interfering with base station tracking.

How back-facing hits work

SteamVR Lighthouse base stations emit infrared laser sweeps that are detected by photodiode sensors on headsets and trackers. Each sensor has a known facing direction, defined as a normal vector in the device's configuration[1]. When a laser sweep is detected, the system expects the signal to arrive from the direction of a base station, consistent with the sensor's orientation.

A back-facing hit occurs when a sensor detects a signal from a direction that does not match its facing orientation relative to any base station. SteamVR drops these hits and logs them with messages such as Dropped 2977 back-facing hits, 10 non-clust. This is usually caused by infrared light bouncing off reflective surfaces in the environment, such as mirrors, windows, glossy monitors, or polished furniture, before reaching the sensor.

Checking back-facing hits

SteamVR log files

Back-facing hit counts are recorded in the vrserver log files.

  1. Navigate to C:\Program Files (x86)\Steam\logs.
    • On Linux, the default log location is ~/.steam/steam/logs.
  2. Open vrserver.txt for the most recent session, or vrserver.previous.txt for the previous session.
  3. Search for the text back-facing hits.

Alternatively, generate a system report from SteamVR:

  1. Open the SteamVR desktop menu.
  2. Select Create System Report.
  3. Review the log output for back-facing hits.

SteamVR web console

The SteamVR web console displays back-facing hit counts in real time when a tracker is powered off.

  1. Open the SteamVR desktop menu.
  2. Select Developer → Web Console.
  3. Power off a tracker to see its back-facing hit count displayed in the console.

Interpreting the values

Lower back-facing hit counts indicate a cleaner tracking environment. When evaluating these numbers, keep the following in mind:

  • Session length affects the count. A longer VR session naturally accumulates more back-facing hits. Comparing values across sessions of different lengths can be misleading.
  • Number of base stations affects the count. More base stations emit more infrared light, which increases the opportunity for reflections.
  • There is no universally defined threshold. Counts in the tens of thousands or higher during a typical session may indicate the presence of reflective objects and are often reported alongside tracking issues.

To isolate problem areas, power trackers on and off in different positions within the play space while monitoring the web console. This can help identify specific zones where reflections are more prevalent.

Common causes

Back-facing hits can be caused by:

  • Reflective surfaces in or near the play space, such as mirrors, glass, windows, glossy monitors, TV screens, or polished furniture.
  • Reflective accessories on the headset or trackers, such as straps, clips, or cases that reflect infrared light.
  • Covered or obstructed sensors on the tracker, preventing proper signal reception.
  • Damaged base stations, particularly a scratched or degraded infrared filter on a base station's front panel.
  • Faulty tracker sensors or other hardware defects on the tracking device.

Reducing back-facing hits

  • Cover or remove reflective surfaces near the play space. Curtains over windows and matte covers on monitors can help.
  • Reposition base stations so they face fewer reflective objects.
  • Ensure tracker sensors are clean and unobstructed.
  • Check base station front panels for scratches or damage.
  • Ensure that straps and mounts on headsets and trackers do not cover or reflect onto sensors.

See also

References

  1. ↑ The JSON File (Lighthouse Devices) on the ValveSoftware/openvr wiki. Describes sensor geometry including modelNormals (per-sensor facing directions).
Retrieved from "https://wiki.vrchat.com/index.php?title=Guides:Lighthouse_back-facing_hits&oldid=67849"