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Showcase lighting (3D)

About this app

Exhibition room in 3D with a desk or tall showcase, a draggable ceiling spotlight and a visitor. The reflection zone on the ceiling shows from where a spotlight appears as a reflection in the glass; the visitor-view panel shows what the visitor sees. Illuminance E = I·cos θ/d², annual exposure in lx·h and glare are checked live against guidelines after CIE 157.

Reflections, illuminance and light exposure

Lighting a showcase raises two questions. First: does the spotlight reflect in the glass? A visitor sees a reflection when the mirror image of the spotlight in the plane of the glass lies on their line of sight through the pane. Second: how much light can the object take? Illuminance follows E = I · cos θ / d², and because light damage adds up over time, the annual exposure in lux hours is what counts. The CIE 157 recommendation gives 50 lx and 15,000 lx·h per year for highly sensitive objects such as paper or photographs.

What the app shows

An exhibition room in 3D with a desk case (tilted glass top, object lying) or an upright case (vertical front pane, object standing), a draggable ceiling spotlight and a visitor. The reflection zone appears on the ceiling: every spotlight position from which a reflection reaches the eye. The “eye view” panel shows what the visitor sees. Illuminance, annual exposure and glare are checked live against guideline values, and false colours on the object show where it is too bright.

What you can try

Drag the spotlight into the reflection zone and out again: the reflection disappears while the lux value on the object hardly changes. Change the visitor’s position and eye height, and the reflection zone moves with them. Choose paper, textile, painting or stone, set luminous intensity, beam angle, opening hours and daylight, and compare the annual exposure with the guideline. The glare check is simplified: it flags spotlights up to 30° above the line of sight.

Frequently asked questions

How do you avoid reflections in display cases?
A reflection appears when the mirror image of a light source in the glass lies on the viewer’s line of sight. You avoid it by placing spotlights outside that area, the reflection zone, which follows from the tilt of the glass, the viewing position and the eye height. Tilted panes, a dark room opposite the case and anti-reflective glass also help. The amount of light on the object hardly depends on whether a reflection is visible.
How much lux can paper take in an exhibition?
According to CIE 157:2004, highly light-sensitive materials such as paper, silk, watercolours and photographs should get at most 50 lx and an annual exposure of 15,000 lx·h. Textiles also get 50 lx but 150,000 lx·h per year, oil paintings and wood 200 lx and 600,000 lx·h; stone and metal are insensitive. 50 lx looks bright enough in a darkened room because the eye adapts.
How do you calculate the illuminance of a spotlight?
For a point light source the inverse square law applies: E = I · cos θ / d². Here I is the luminous intensity in candela, d the distance in metres and θ the angle between the light ray and the surface normal. A 400 cd spotlight at 2 m distance gives 100 lx at normal incidence. The annual exposure is the illuminance times the opening hours, measured in lux hours.
What can I try in the showcase lighting app?
You choose a desk case or an upright case and an object made of paper, textile, oil paint or stone, drag spotlight and visitor around the room and set intensity, beam angle, eye height, opening hours and daylight. The app shows the reflection zone on the ceiling, the visitor’s view, the illuminance, the annual exposure against the guideline and a simplified glare check.

Subject: Architecture & scenography

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