The short answer: Yes, a sun tunnel works on a cloudy day, because it collects daylight rather than direct sun. The light is softer and there is less of it, so the room will look dimmer than on a clear morning. On a very dark, wet afternoon you will still want the lights on. A sun tunnel takes the edge off a gloomy room; it does not replace the switch.
Brighton and Hove sees plenty of grey weather, so this is a fair question to ask before you commit. It is part of our wider set of answers on sun tunnels. Below we explain what happens to the light in cloud, what you will notice in the room, and what you can do to get the best from a tube.
Daylight is not the same as sunshine
A sun tunnel, a compact kind of skylight, does not need the sun to shine on it. It catches light from the whole sky. On a clear day that includes a bright patch where the sun sits. On an overcast day the cloud spreads the light across the sky, so the dome still receives it, just at a lower level.
This is the same light that comes through any window on a cloudy day. Your sun tunnel is subject to the same changes in brightness. If the sky gets darker, the diffuser gets dimmer with it.
What you will notice indoors
On a bright day, the diffuser glows clearly and the room feels well lit. On a cloudy day, the glow is gentler. You can usually still see to wash your hands, find clothes in a wardrobe or walk along a landing without a lamp, but you may want one for reading or for detail work.
The change from day to day is gradual rather than sudden. Because the light is spread evenly by the diffuser, a grey day does not make the room look gloomy in patches. It just looks quieter and cooler than usual.
| Sky | What you see |
|---|---|
| Clear sky | A bright, even glow |
| Thin high cloud | A slightly softer glow |
| Heavy overcast | A dim glow; lights helpful for tasks |
| Dusk or storm | Little light; lights on |
Things that help on a dull day
A few choices make a real difference to how the tube performs when the sky is grey.
- A shorter, straighter run, because the light has less distance to lose. See how long a sun tunnel can be.
- A rigid tube with a polished inside, which reflects light well. The trade-offs are covered in rigid or flexible sun tunnels.
- A dome placed where trees, a chimney or a taller neighbour will not cast shade across it.
- A clean dome. Moss and a film of dirt on the outside reduce what gets in.
Roof position and shade
The spot on the roof deserves real thought at the survey. A dome on the north-facing slope receives little direct sun, but in cloud the difference between slopes shrinks, because the light is coming from everywhere. What does hurt, in any weather, is shade from a parapet, a dormer or a neighbouring building. In dense streets of tall terraces, a position near the ridge or on the sky-facing side often collects the most light.
Winter and the shorter days
The season matters as much as the cloud. In midwinter the sun is low and the days are short, so a sun tunnel has fewer hours of useful light to pass on. You may find the diffuser looks dull by mid-afternoon, when it was cheerful at noon in June. That is the sky, not a fault in the unit.
Many households treat the sun tunnel as the daytime light and keep the ceiling lamp for evenings. If you plan the room that way, a modest tube is enough. If you expect it to do more than that in winter, tell us at the survey, and we can talk through a wider tube or a different product.
Fitting a bulb behind the diffuser is an option some people consider so the same opening serves at night. Whether that suits your ceiling depends on the unit, and we would discuss it at the survey rather than promise it here.
Glare, heat and the bright days
People sometimes worry about the opposite problem. A sun tunnel is small, and the diffuser spreads the light, so glare and overheating are rarely issues in the room below. The dome itself is also modest in size, so it does not behave like a large south-facing glass roof. That makes a tube a gentle product on bright days as well as dull ones.
Where it works best
Because a sun tunnel does not rely on strong sun, it suits rooms that need a gentle level of daylight all year round. Bathrooms, landings, hallways and wardrobes are the usual choices, and we go through them in sun tunnels for hallways, landings and bathrooms.
If you are hoping for a bright, open room, a larger glazed unit may serve you better. Compare it with a roof lantern or a flat roof rooflight, or read whether sun tunnels are worth it for your room.
Getting one fitted
Cutting the opening for a sun tunnel counts as building work. If the tube is notifiable, the Building Control notification is ours to send, and you can read the details in our Building Regulations guide. Rules on planning are in the planning permission guide. Flats are treated differently, so see rooflights in flats and leasehold buildings if you are a leaseholder.
We start with a free survey and finish with a written quote at a fixed price. The quote includes a written access plan covering how we reach the roof. If you would like us to look at a dark room, request your free survey. For other questions, return to the sun tunnels hub.
