Sun tunnels and skylights both solve the same basic problem: a room with no natural light. But they solve it in different ways, and the right choice depends on where the dark room actually is in your house. A sun tunnel channels daylight down a reflective tube from the roof, with no direct view of the sky and no opening window. A skylight, or rooflight, sits directly over the room and can offer a full view, ventilation, and considerably more light.
Toughened Glass Systems doesn’t sell sun tunnels. We supply rooflights, roof lanterns and skylights, so this comparison is written from that position rather than pretending to be neutral about a product we don’t stock. Where a sun tunnel is genuinely the better fit, we say so. Where a rooflight solves the problem better, which is most of the time once there’s roof access directly above the room, we’ll show you which type and what it costs.
What’s the difference between a sun tunnel and a skylight
A sun tunnel, also called a tubular skylight or light tube, uses a small dome or flat lens on the roof to capture daylight, then reflects it down a rigid or flexible tube into a ceiling diffuser. There’s no glazed opening into the room itself, just a light fitting in the ceiling. They’re typically 250mm to 550mm in diameter and can travel several metres through a loft space before reaching the room below.
A skylight or rooflight is a glazed unit set directly into the roof, either flush with a flat roof on a raised upstand or fitted within a pitched roof slope. It sits directly above the room, so you get a real view of the sky, the option to open it for ventilation on most models, and far more glazed area than a tunnel’s small lens can capture.
The core distinction is proximity. A sun tunnel works because the room doesn’t need to be directly under the roof, the tube does the work of getting light there. A skylight only works where the room is directly beneath usable roof space.
Where sun tunnels genuinely win
There are rooms where a rooflight simply isn’t an option, and a sun tunnel is the right call. This is worth being upfront about rather than trying to talk you out of it.
- Internal rooms with no roof directly above them. A ground-floor hallway or downstairs WC under an upstairs bedroom has no roof access at all. A sun tunnel’s tube can be routed through the loft and down an internal wall void to reach it; a rooflight physically can’t.
- Small enclosed spaces. Walk-in wardrobes, understair cupboards converted to shower rooms, and similarly tight footprints often can’t accommodate a rooflight’s minimum unit size or upstand, but a compact tunnel lens fits easily.
- Budget-driven single-room fixes. If the only goal is to stop switching a light on in a windowless landing, a sun tunnel is a smaller, faster, cheaper job than reworking a roof structure for a rooflight.
- Minimal disruption. Installation typically takes under a day, with much less internal mess than fitting a rooflight, since there’s no upstand to build and no plasterboard reveal to finish out.
If your dark room fits one of these, a sun tunnel is a sensible choice and we’d say so even though we don’t sell them.
Where a rooflight is the better choice
For any room that sits directly under a usable section of roof, a rooflight does more than solve the darkness problem. It’s worth understanding what you’d be giving up by defaulting to a tunnel out of habit.
- Ventilation. A sun tunnel is a sealed unit; it moves light, not air. Most rooflights, including our opening rooflights range, can be manually cranked or electrically operated to vent stale air, which matters far more in a bathroom or kitchen than in a hallway.
- Volume of light. A tunnel’s lens typically caps out around 550mm across. Even TGS’s smallest Flat Rooflight starts well above that footprint and scales up to several square metres, delivering a genuinely different quantity of daylight into the room rather than a single bright point on the ceiling.
- A sky view and architectural value. A tunnel’s diffuser looks like a light fitting. A rooflight looks like a window in the roof, with a direct view out and a material impact on how a room feels, which is part of why rooflights are widely considered to add value to a home in a way a hidden tube doesn’t.
- Product choice for the room. Where a sun tunnel is essentially one product in a few sizes, rooflights come in enough configurations to be matched to the room rather than the room being made to fit the product, covering everything from bathroom skylights and kitchen skylights to pyramid skylights for even light spread through the day, and smaller rooflight formats sized closer to a tunnel’s footprint for tighter rooms that do have roof access.
Light quality: diffuse versus direct
This is the part most comparisons gloss over, and it’s the genuine technical trade-off between the two products, not just a cost or size difference.
A sun tunnel’s tube scatters light as it travels, so what reaches the room is soft, even, and shadow-free, closer to a very bright overcast day than direct sun. It doesn’t carry meaningful heat with it, and there’s no glare to manage. That’s genuinely useful in a small bathroom where you don’t want a hot spot on the ceiling.
A rooflight lets direct sunlight into the room, which is brighter, changes character through the day, and can bring real heat gain in summer, particularly on a south-facing roof. That’s manageable, most buyers pair larger rooflights with blinds or manage summer heat gain directly, but it’s a genuine consideration a sun tunnel simply doesn’t have.
Cost and installation compared
Sun tunnel pricing varies by tube length, diameter and roof type, and is usually quoted per job by an installer rather than sold as a fixed product, so treat the figures below as a general guide rather than a fixed price. Rooflight figures are real prices from TGS’s own range, correct at time of writing.
| Sun tunnel | Rooflight (TGS range) | |
| Typical cost | Generally the lower-cost option of the two, though exact pricing depends on tube length and roof type | From £163.00 ex VAT for a small Triple-Glazed Self-Clean Rooflight, up to several thousand for larger or opening units |
| Installation time | Typically under a day | Standard-size units can usually be fitted by a competent builder in a day; larger units, roof lanterns and made-to-order sizes take longer and may need structural assessment |
| Product lead time | Not applicable, sun tunnels are typically sourced through the installer | From 1 to 3 working days on some standard TGS sizes, up to several weeks on made-to-order or larger units |
| Structural work | Minimal, no upstand required | Requires an upstand on a flat roof or a properly sized opening on a pitched roof |
| Ventilation | None | Available on most opening ranges |
| Sky view | None, diffused light only | Full sky view |
| Suitable rooms | Any room, including those with no direct roof access | Rooms directly beneath usable roof space |
The pattern worth noting: a sun tunnel is the cheaper, faster fix specifically because it does less. It solves darkness. It doesn’t solve ventilation, doesn’t give a sky view, and can’t scale up to genuinely open a room the way a larger rooflight does.
Which rooms suit which option
- Bathrooms. If the bathroom sits directly under the roof, a rooflight from our bathroom skylights range is usually the stronger choice because it can vent moist air out, which a sealed sun tunnel can’t. A ground-floor cloakroom or WC with no roof above it is where a sun tunnel earns its place instead.
- Hallways and landings. This is the classic sun tunnel scenario when the hallway is internal or on a lower floor. Where the landing does sit directly under the roof, particularly in a loft conversion, a compact rooflight from our rooflight loft conversion guide will usually outperform a tunnel on light volume for a similar footprint.
- Kitchens. Kitchens generate heat, steam and cooking odours, all of which benefit from an opening rooflight far more than a sealed tunnel. See our kitchen skylight guide for sizing a unit to a kitchen extension or existing flat roof.
- Lofts and small box rooms. Where roof access exists but the room is tight, our smaller rooflight range is worth checking before defaulting to a tunnel; see also our guide to rooflights for smaller spaces.
- Walk-in wardrobes and understairs conversions. These rarely have usable roof directly above them and are a genuine sun tunnel use case.
Planning permission and building regulations
Most rooflight installations in England and Wales fall under permitted development, meaning planning permission usually isn’t required provided the unit doesn’t project more than 150mm above the existing roof plane. Our building regulations and planning permission guide covers the full conditions, including the exceptions for listed buildings and conservation areas.
Sun tunnels typically fall under the same permitted development allowances, since the roof-level component is usually a small, low-profile dome or lens rather than a projecting window. As with rooflights, this can change for listed buildings or properties with an Article 4 direction removing permitted development rights, so it’s worth checking with your local planning authority if either applies.
Can You Use Both?
Yes, and in a lot of houses the right answer is both rather than either. A common pattern is a rooflight, such as TGS’s own Flat Rooflight or Triple-Glazed Self-Clean Rooflight, over the kitchen or bathroom where there’s real roof access and ventilation matters, paired with a sun tunnel over the internal hallway or landing that has neither. Treating this as a room-by-room decision, rather than picking one product for the whole house, usually gives a better result than trying to force one solution everywhere.
Choosing the right product for your room
If your dark room sits directly under a usable roof, browse our full rooflights and skylights range or start with our flat roof skylights category if you’re working with a flat or near-flat roof structure. Our buying guide to skylights for flat roofs covers pricing, U-values and lead times across the whole range in more depth.
If a sun tunnel is genuinely the right fit for your room, a local roofer or specialist tunnel installer is the right next step rather than us, and we’d rather tell you that directly than sell you the wrong product.
Need help working out whether your room suits a rooflight? Contact our team for advice, or call 0203 633 3224.
Related guides
- Best Skylights for Flat Roofs: Complete Buying Guide
- Rooflights vs Roof Lanterns
- What’s the Difference Between Skylights, Rooflights and Roof Windows?
- How to Increase Natural Light in a Room
- Best Roof Lights for Smaller Spaces
- Top Benefits of Skylights
- Rooflight and Skylight Cost: A Complete Guide
- Building Regulations and Planning Permission for Rooflights
- Rooflight Loft Conversion Guide
Frequently asked questions
Do sun tunnels let in heat like a skylight can?
No, not meaningfully. Because the light travels down a reflective tube rather than through open glazing, a sun tunnel carries very little heat with it, which is one of its genuine advantages over a rooflight in a small, hard-to-ventilate room.
Can a sun tunnel be opened for ventilation?
No. A sun tunnel is a sealed light-transfer system with no opening into the room. If ventilation is a priority for the space, an opening rooflight is the only one of the two options that provides it.
Do sun tunnels work on a north-facing roof?
They still work, but with less light than a south-facing installation, since output depends on how much direct sun reaches the roof-level lens. The same principle applies to rooflights: a north-facing unit provides softer, more consistent daylight rather than direct sun.
Is a sun tunnel cheaper than a rooflight?
For a single small dark room with no roof access, yes, generally. Once you’re comparing a sun tunnel against one of TGS’s smaller fixed rooflights for a room that does sit under usable roof, such as the Triple-Glazed Self-Clean Rooflight from £163.00 ex VAT, the gap narrows considerably.
Do rooflights need more maintenance than a sun tunnel?
Slightly, yes. A rooflight has external glass to keep clean and, on opening units, hardware to check periodically, whereas a sun tunnel’s roof-level dome is smaller and its internal diffuser rarely needs attention. Neither requires significant ongoing maintenance under normal conditions.
Can I fit a sun tunnel and a rooflight in the same house?
Yes. Most houses that use both do so by room function: rooflights over rooms with roof access and a genuine need for ventilation or a sky view, sun tunnels over internal rooms with neither.