Skip to content

Measure ambient light, illuminance and uniformity

Use this page to take the room and screen measurements that many display standards ask for. The results appear in the results panel, in the History tab and on your reports.

Measurement What it measures Typical use
Ambient luminance (Lamb) Room light reflected off the screen, in cd/m² Used in every calibration. Most standards expect 0.2 to 1.0 cd/m² in a reading room.
Illuminance Room light falling on the screen, in lux Checks that the room lighting suits image reading.
Uniformity How evenly bright the screen is from the centre to the edges, in % Finds displays that are brighter in some areas.

Measure ambient luminance

  1. Turn the display off, or make it show black.
  2. Check that the diffuser cover isn't over the photometer's sensor.
  3. On the display's card, click Measure Ambient Luminance.
  4. Hold the photometer where a person reading images would sit, with the sensor facing the screen.
  5. Click to measure.

ViziCAL saves the value for the display and uses it in its next calibration. If the value is more than the standard recommends, ViziCAL asks you to dim the room lights and try again.

You can also type the value yourself: click the edit button next to Lamb in the results panel, type a value between 0.0 and 5.0, and click OK.

Measure illuminance

  1. Turn the photometer's diffuser cover so it covers the sensor.
  2. Hold the photometer against the screen, with the sensor facing away from the screen, into the room.
  3. On the display's card, click Measure Illuminance (Lux).

If your photometer can't measure illuminance, ViziCAL offers to use another connected photometer that can, for example an X-Rite model.

Measure uniformity

  1. On the display's card, click Measure Uniformity.
  2. Place the photometer on the screen where ViziCAL shows the patch.
  3. Move the photometer to each position as ViziCAL asks. If Uniformity check - beep to move is ticked in Calibration Settings, ViziCAL beeps when it's time to move.

When it's finished, the result is the largest difference in brightness across the screen, as a percentage.

Common problems

ViziCAL says the diffuser is in the wrong position
Luminance measurements need the diffuser away from the sensor. Illuminance needs it over the sensor. Turn the cover and try again.
ViziCAL says the photometer doesn't support ambient luminance or illuminance
Connect a photometer that does, for example an X-Rite model, and try again.