Illuminance chart card with background

Who it’s for

Building managers, facilities engineers, and greenhouse operators ask “how has light changed over the selected period?” They want the trend and delta in one card displayed over a background image for dedicated building management or reception screens.

What it does

A sensor averaging 42 lx this week versus 60 lx last week shows a red-orange value — Bright — with a -30% delta and a -18 lx absolute change, plus a chart of readings, displayed over the preset background image.

• Large current illuminance value color-coded across five bands from Dark to Very Bright
• Delta percentage and absolute delta comparing the current period to the previous one
• Time-series chart of illuminance readings averaged per interval
• Decorative background image bundled with the widget, with a white overlay that keeps the text readable
• Shows one sensor’s data; it does not compare multiple zones

How to set up

Data keys

Key	Role	Type	Description
illuminance	Chart series	Timeseries	Illuminance in lx; drives the chart and all derived overlays
Latest	Latest value	Timeseries	The headline figure above the chart. Its own color ranges are where the band colors are edited
Delta percent	Percentage change	Timeseries	Change against the previous period, as a percentage
Delta absolute	Absolute change	Timeseries	Change against the previous period, in the key’s own unit

The widget ships with a simulated function datasource key labeled Illuminance, so it draws random values until you point the datasource at a device and rename the key.

To point it at your own device: open the dashboard in edit mode, open the widget’s Datasources, pick the entity or entity alias, and replace the function key with the key your device reports.

If the key has never reported for the selected time window, the chart is empty and all overlays show no data.

Value ranges

Range (lx)	Level	Color
< 1	Dark	Dark Gray
1–5	Low	Orange
5–20	Moderate	Orange
20–50	Bright	Red-Orange
50+	Very Bright	Red

How to customize

• To swap the background image — open the widget settings and set Background to a different image or switch to a solid color.
• To adjust how much the background shows through — change the Overlay opacity; lower values reveal more of the image, higher values push it further back.
• To use your own illuminance thresholds — edit the color ranges on the Latest data key; adjust the five default bands to match your facility’s targets.
• To change the comparison period — adjust the Time window on the dashboard; the delta automatically compares to the equivalent preceding period.
• To hide or show the chart — toggle Show chart in the widget settings.
• To change the chart line color — set Chart color.
• To hide the entity name subtitle or the timestamp — turn off Show subtitle or Show date.

Tips

• A falling delta on a plant-growth dashboard warns that supplemental lighting may have dimmed or failed — useful for catching issues before crop yield suffers.
• If the background image reduces contrast, raise the Overlay opacity to keep the text readable from a distance.