How Do Sun Tunnels Work?


Roof windows are the perfect solution to add natural light to your home, creating an open feel and giving even the darkest rooms a new lease of life. But what can you do if your darkest room isn’t on the top floor? That’s when sun tunnels come in handy.

What is a Sun Tunnel?

A sun tunnel is a small window installed into your roof that is attached to a tube that transports the light from your roof to a room elsewhere on your property. Once the light reaches the room a light diffuser causes the light to spread out and illuminate the room with natural light.

Sun Tunnel on Roof

How Do Sun Tunnels Work?

These light tubes might sound miraculous, but really, they are very simple. Light enters through the window on your roof, then gets bounced down the tube, which is lined with highly reflective materials, such as aluminium. Once the light reaches the diffuser, it hits the curved, prismatic material at all angles to spread the light throughout the room.

Things to Consider

While sun tunnels are a simple and easy way to get natural light into rooms that wouldn’t normally receive natural light, there are certain aspects of your sun tunnel that you can control to get the optimum amount of natural light.

Window Type

There are two types of window that are commonly available for sun tunnels; domed and flat. Domed windows are better for allowing more light to enter the light tube as the rounded shape results in less light being reflected off the glass. However, domed windows protrude out from the roof so may not be aesthetically appealing. On the other hand, flat windows will reflect more light off the glass however blend in with your roof to look less obvious.

Window Positioning

To get the most natural light from your sun tunnel, it is important to consider the positioning of the window on your roof. If you have a pitched roof and are lucky enough to have a south facing roof, this is the best place to position your sun tunnel. If you can’t position your sun tunnel towards the south, you can still get plenty of ambient light from North, East and West facing roofs.

Properties with flat roofs can also benefit from sun tunnels as the sun will shine on them all day long. The best position for a flat roof is to be directly above the room the tunnel is directed towards to keep the tube as short and straight as possible.

While you’re thinking about the positioning, you should also consider any obstructions that may block the natural light – such as trees and shadows from other houses – and avoid them!

Sun Tunnel Diagram

Tube Type

The reflective light tubes in a sun tunnel are available as rigid tubes that cannot be moved or as a flexible tube that can be moulded around obstructions or awkward spaces.

Rigid tubes have better light transmittance, meaning more natural light will reach the desired room. This is because it channels light in the right direction and reduces the number of times the light needs to bounce off the reflective walls. Due to this, rigid tubes are up to 20m long!

While a flexible tube results in less light reaching the tube, they are needed if there is an obstruction preventing your tube from being straight. Flexible light tubes are also much cheaper than their rigid counterpart making them a good choice for those on a tighter budget.

Tube Size

When choosing the size of your sun tunnel, you need to make sure you choose the right diameter size for your reflective tube. A wider diameter means more light can enter the tube and less bounces for the light to get to the intended room. However, a smaller diameter is easier to fit into your property, so if you’re tight on space, a thinner tube is better for you.

The length of the reflective tube in your sun tunnel can greatly affect the amount of light that reaches your room. A longer tube means there is further for the light to travel and therefore more bounces needed to get to the other side. This results in less natural light reaching your diffuser and a dimmer room.

How Sun Tunnels Work

Advantages of a Sun Tunnel

  • Easy to Install – Due to their small size and lightweight structure, sun tunnels are easier to install than typical roof windows as they fit between the trusses and rafters without the need for reinforcing.
  • Natural Light – Sun tunnels are a great way to allow natural light to reach a room that it could not before. This will brighten up dark spaces and reduce electricity bills.
  • Better Thermal Performance – As there is a smaller opening in the roof, sun tunnels have better thermal performance than roof windows, resulting in less heat lost through the window. 

Disadvantages of a Sun Tunnel

  • Varying light – relying on natural sunlight means your room will not always be lit, this can be a particular problem in winter with short daylight hours or if the window gets obstructed.
  • No ventilation – As the window of a sun tunnel cannot be opened like a roof window, they do not allow for ventilation in your room.
  • Price – Sun tunnels can be more expensive to buy than a typical roof window, however the cost of installation tends to be lower.


Take a look into our other blog articles such as best roof windows or how to install a roof window.