"Reflected Light From Below" Error Guidance

During field calibration, the instrument must observe internal reference signals using its optical system. These measurements depend on clean, controlled light paths.

The “Reflected Light From Below” error appears when unwanted light enters the optical path from below the instrument, interfering with those measurements.

In simple terms:

The instrument is seeing light it did not expect, coming from the wrong direction.

When this happens, the calibration measurements become unreliable, and the instrument stops the process to protect accuracy.

This error is almost always linked to environmental conditions, not a defect in the tool.

Typical causes include:

Highly reflective surfaces beneath the tool

It may be subtle, but the below common surfaces do reflect light:

• Polished concrete
• Epoxy or sealed floors
• Metallic decking or steel plates

Strong sunlight reflecting upward

This is especially true when the tool is positioned over:

• Light‑colored ground
• Water
• Snow or ice

Direct light sources below the instrument

Observe your work area and search for things such as:

• Work lights placed on the floor
• Uplighting on indoor sites
• Direct sunlight entering from low angles, such as early morning or late afternoon sun

In all of these cases, light reflected upward can enter the instrument and disrupt the calibration optics.

Field calibration requires clean, repeatable optical measurements. Reflected light introduces glare and false signals, making it impossible for the instrument to distinguish valid reference data.

If calibration were allowed to continue under these conditions:

• Alignment values could be calculated incorrectly
• Geometric corrections could be corrupted
• Accuracy loss could occur without obvious warning

Instead of risking this, the instrument stops calibration and alerts you.

What light must the tool be able to see?

Best Methods to Resolve: Reduce Reflected Light

Change the setup location

If possible, move the instrument slightly to a location where the surface below is:

• Darker
• Less reflective
• Matte rather than glossy

Even moving a meter or two can significantly reduce reflected light.

Shade the area beneath the instrument

If relocation is not possible:

• Place a non‑reflective material (cardboard, fabric, matte cover) on the ground below the tool
• Block direct sunlight from hitting the floor beneath the instrument

This often resolves the issue immediately.

Adjust timing if working outdoors

If the sun is low in the sky:

• Wait until the sun angle changes
• Avoid calibration during early morning or late afternoon if glare is present

Turn off or reposition work lights

Ensure that no lights are shining upward toward the instrument during calibration.

Repeat the calibration

Once reflected light is reduced or eliminated, repeat the field calibration. In most cases, calibration will complete successfully once optical conditions are clean.

What This Error Does Not Mean

This error does not indicate:

• A hardware failure
• Dirty mirrors inside the instrument
• A problem with the compensator
• A permanent limitation of the tool

It is a situational optical condition, and once corrected, normal operation can resume immediately.

Final Reminder

The “Reflected Light From Below” message is a protective measure. It prevents optical interference from silently degrading calibration results.

By controlling light conditions around and beneath the instrument, you allow the calibration process to complete correctly and keep your measurements trustworthy.