A light tunnel captures daylight outside and transports it through a highly reflective tube to a diffuser in the ceiling. Unlike electric lighting, the amount of light follows the weather, season and time of day. Output is higher in bright conditions than on a dark winter day.

Intura SunTube uses a crystal glass dome on ST25 and ST35 and a reflective tube with 99.8% reflectance. A well-designed route therefore retains much of the captured daylight. The diffuser distributes the light in the room and prevents a direct view into the tube.

Output cannot be expressed as one fixed wattage or lumen figure. Diameter, available outdoor light, orientation, shade, tube length, bends, ceiling height and interior colours all affect the result. As a guide, ST25 can serve a small room of up to approximately 9 m², ST35 approximately 13–16 m² and ST55 approximately 25–30 m².

Under favourable conditions, an ST35 may provide approximately 900–1300 lux in summer and 400–700 lux in winter, measured 1.5 metres below the diffuser. These values are indicative and are not guaranteed for every project situation.

Extension tubes can be used to create a run of up to approximately 6 metres. A longer route creates more reflection losses and makes good positioning increasingly important. For a long run, consider a larger diameter and keep the tube as straight as possible.

Measure from the external unit to the finished ceiling and account for the roof build-up, insulation, suspended ceiling and connections. A bend also changes the effective length required.

Adjustable 0–45° bends make it possible to pass around a beam, pipe or another obstruction. Several bends may be technically possible, but every change of direction reduces daylight output. Limit both the number and angle wherever possible.

Before forming the roof opening, check that the entire route is clear. A small adjustment to the position of the external unit or diffuser can sometimes avoid an additional bend and improve performance.

ST25 and ST35 have a crystal glass dome. Crystal glass does not yellow under UV exposure and retains its clarity. Its hard, smooth surface withstands weathering and dirt adheres less readily than to many plastic surfaces. Rain on glass also generally creates less drumming noise than rain on a thin plastic dome. The larger ST55 uses a PMMA dome.

Keep the dome and surrounding area free from heavy soiling, leaves and permanent shade. Its position on the roof has a major effect on the amount of daylight the system can capture.

A light tunnel penetrates the thermal envelope. EcoPower adds 14 cm of PIR insulation and an insulated glass closure, greatly reducing heat transfer and the risk of a cold surface. This is particularly relevant in heated rooms, well-insulated roofs and new builds.

The choice between HR++ double and HR+++ triple glazing depends on the required U-value and project standard. Provide continuous insulation and an airtight connection around the element; a high-performance product cannot compensate for poor installation.

An optional LED module allows the same ceiling position to be used as a light fitting after dark. During the day, light comes from outside; the LED can take over when insufficient daylight is available. An optional dimmer can reduce the natural daylight when a darker room is required.

Plan the power supply, controls and accessibility before installation. Electrical components must be connected in accordance with applicable regulations.

• Considering only floor area while ignoring tube length and bends.
• Positioning the external unit in permanent shade from a roof structure or tree.
• Checking the route only after the roof opening has been formed.
• Using too many or unnecessarily sharp changes of direction.
• Underestimating the thermal and airtight connection around the roof penetration.
• Ordering the wrong version for the roof covering or roof type.
• Treating daylight as a constant replacement for all electric lighting.

If in doubt, have the configuration checked in advance. Include the roof type, roof covering, dimensions, photographs and a sketch of the intended route.