The Expected Lighting Module (ELM) maintains a record of the anticipated brightness level for all fixtures. When the controller issues a lighting command, it performs three key functions:
- Updates the expected level for the target device
- Confirms the device responded as intended
- Continuously monitors for unexpected state changes
The ELM can be configured to automatically issue correction commands when it detects a device operating at an incorrect level.
Troubleshooting: If you observe ELM mismatches or fixtures at unexpected levels, this typically indicates that devices are being affected by external factors (such as manual overrides, physical switches, or other control systems).
You can enable the ELM's automatic correction feature to restore devices to their expected levels when discrepancies are detected.
Configuring behaviour to correct the light level.
To configure the ELM behaviour for a control gear, use the Device Types->ECG view and find the correction field.
The Default behaviour is only used if you have specified a Driver Type in the ECG view. The Driver Type field allows you to tell the system to apply stringent rules on the device, to keep it on. For more information on this, see this article.
Aside from this, the ELM system offers combinations of three configuration options: disabling monitoring entirely, displaying detected inconsistencies only (show issue), or automatically adjusting device levels when discrepancies occur (act on mismatch).
Understanding ELM Detection Timing:
When a fixture changes state unexpectedly, the system may take several minutes to detect and correct the issue. However, any lighting command you send will trigger an ELM verification check shortly thereafter, expediting detection.
Important Limitation:
While ELM correction helps manage problematic situations, it is not a substitute for addressing the root cause of unreliable device behavior. Issues such as firmware bugs, power interruptions, or lamp failures require proper resolution. Clients typically find intermittent light malfunctions—even with automatic correction—unacceptable, as they expect consistent and reliable lighting performance without visible disruptions.
Default Configuration:
- Wireless controllers: Preconfigured to both detect discrepancies and automatically apply corrections
- DALI wired controllers: Set by default to detect issues only, without automatic corrective action
Seeing an incorrect level in the monitor
Example of the monitor output - the controller expects the device to be at arc power 230, but finds it to be at arc power 0 (light off).
Potential Causes
- Relay-controlled devices recently powered off/on, now at power-on level (The ELM does not know if a control gear is controlled by a relay and will report a mismatch for this legitimate, but unexpected behaviour).
- General power cycling causing devices to revert to power-on level
- System failure level activation
- Lamp malfunction
- Command misinterpretation (common in pre-DALI 2 certified devices)
- Changes via another mechanism that does not notify the DALI bus that a light command has been initiated (ie, an internal sensor that modifies the lighting state).
- Firmware bugs in the device, in general.
Troubleshooting Steps
- Configure unique values for power-on and system failure levels (e.g., 254 for power-on, 253 for system failure). If the device is found to be at that level, you can conclude that the system failure feature of the device has fired.
- Run monitoring filtered for "ELM Mismatch," then filter for lighting commands to check for device-directed instructions. If you do not find any specific commands to send the device, you might find that they have misinterpreted 24bit commands as 16bit or other rather difficult to diagnose issues with device firmware.
- Check power / dali supply
- Check that lamps are within spec for ballast
If individual lights within a group are functioning incorrectly and the controller is set to communicate via group commands only, the issue likely lies with the devices or wiring.
Special cases
If an instruction can produce differing results, such as GO TO LAST ACTIVE LEVEL or a dim (which can often cause difference in rounding), the ELM will polls the light shortly afterward and set the expected state based on the device's response.
This is one example of where the ELM cannot correct a failure.
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