Daylight Without Lamps: Where Light Transmission Pays Back

What the numbers look like

Ranges are typical; confirm per datasheet. What matters is not only how much light passes but how. Opal sheet transmits less yet scatters direct sun into even diffused light, so work surfaces show fewer harsh highlights and shadows — often more useful than a higher transmission figure in assembly or picking areas.

An illustrative saving

Take a 5,000 m² single-storey factory: daylighting strips at 8% of roof area (about 400 m²), existing lighting power density of 6 W/m², ten hours of lighting per day, and six daytime hours no longer needing lamps.

5,000 × 6 W/m² × 6 h × 300 days ≈ 54,000 kWh per year. At industrial tariffs that is a recurring cost, while the incremental cost of the strips happens once. Actual figures depend on local power prices and daylight hours — this shows the method, not a quotation.

Do not ignore cooling

Daylight arrives packaged with heat. In hot climates, solar gain through the roof raises cooling load and can consume the lighting saving. Three responses: choose opal or light tints to cut direct gain while keeping diffused light; limit the daylighting ratio, typically 5–10% of roof area for industrial buildings rather than full coverage; and pair with ventilation, which removes heat far more effectively than thickening the sheet.

The test is net benefit — lighting saved minus cooling added. In temperate climates and daytime-operating buildings it is usually clearly positive.

Four design issues

Glare from direct sun reflecting off machinery — use opal sheet or reposition strips away from directly above workstations. Condensation on the inner face, where multiwall performs better than single skin but still needs slope and drainage. Banding, where widely spaced strips create light and dark stripes; distribute strips evenly rather than concentrating them. Transmission decay, because PC yellows with age and loses light year by year — UV-protected sheet degrades far more slowly, which is why cheap sheet without UV "goes dark" within a few years.

Where it pays best

Daytime factories, warehouses and logistics centres; corridors, walkways and platforms that need light anyway; greenhouses and propagation where internal light drives yield; and car park entrances and stairwells. It pays least in night-shift operations, and in cleanrooms where heat gain and temperature stability dominate.

FAQ

Do daylighting panels leak? Leaks almost always occur at details — lap direction, screw holes, edge closure. An intact panel is waterproof.

What if it darkens after a few years? That is yellowing reducing transmission. Double-sided UV co-extrusion slows it considerably but cannot eliminate it.

Should the strips follow the roof slope? Yes. Keep them in the roof plane with proper laps and sealing so no ponding forms.