Does the reflective value of the tubing make much difference?
Solarspot Vegalux tubes – 99.7% ultra-reflective tubing – standard on all Solarspot systems. You don’t have to be a rocket scientist to understand the significance of the reflective tube and how it will determine the amount of light that is delivered. However, it’s not always that simple to understand the data published by many of the solar tube manufacturers when you read figures like 99.7%, 98%, 96% etc. and think that they all look very similar. Actually, even the difference of a few percent can make a huge difference.
The reflective action of the 99.7% Vegalux material is what is known as specular. This means that when light hits the surface of the material, 99.7% of the light carries on down the tube to the next bounce – only losing 0.3% of energy (light) on each bounce.
The reflective action of materials with less reflectivity, 98%, 96% etc. is what is known as diffuse reflectivity. This means that when the light hits the surface of the material, light scatters and only a percentage of the light carries on down the tube to the next bounce – losing around 5% of energy (light) on each bounce – that’s 16 times less light every time the light bounces.
This specular reflectivity makes the Vegalux material the most reflective tubing in the world.
If you read Solatube’s website you could be forgiven for thinking that this was a material exclusively produced for them under the name of Spectralight Infinity.
If you think about the light bouncing down the tube to get from the top to the bottom, after just 10 bounces of light almost half of the original source light will have been lost.
Compare that with the Solarspot and only around 3% will be lost.
It’s fair to assume that in the winter, and for solar tubes that are longer than a meter or so, the number of bounces will be considerably more. And if you add a few bends into the system, then a tube with anything less than a 99.7% specular reflective surface, will delivery virtually no light at all.
The truth is that it is a material readily available from 3M but as a premium product with a corresponding price tag, unlike Solarspot, most other sun pipe manufacturers opt for cheaper, less efficient alternatives.
Vegalux 99.7% reflective tubing
With Solarspot’s Vegalux® tubing, all of the reflective value is specular. This means that 99.7% of the light that hits the surface bounces off at the angle of incident and only a tiny 0.3% is lost. With this outstanding level of performance no other material reflects more light Vegalux rigid tubing.
98% reflective tubing (Super-silver polished surface)
With 98% reflective ‘polished’ surfaces the reflectivity is part specular and part diffuse. In recent tests by the BRE these materials were shown to have roughly 4% diffuse reflectivity which means that a percentage of the light is scattered at the point of reflection meaning that as much as 6% of the energy is lost on every bounce.
Unlike rigid pipes with a reflective surface on an aluminium tube, flexible-duct systems use a concertinaed foil wrapped over a wire coil. Whilst easy to install, the construction of this sort of sun tunnel means that 50% of the tube surface is angle back up to the sky and so at least 50% of the daylight is lost on every bounce. After 20 bounces of light roughly 95% of the original light is lost.
Frequently Asked Questions
What should I look for when comparing product performance?
Independent, comparative testing using internationally recognised methodology – it’s as simple as that. And the thing to look out for is an efficiency figure. If a manufacturer is confident about the performance of their system they will quote an efficiency figure and then show how this compares to competitor products. Solarspot are the only manufacture of solar tube type systems to publicly publish these figures and that is because we know that, size-for-size, no one else will give you more daylight through a tube.
What does ‘efficiency’ mean, and how does it affect the light delivery?
Efficiency is a measure of the ability of the solar tube to deliver light from the top (dome) to the bottom (diffuser), regardless of the time of day or time or year. To suggest otherwise is like saying your car is faster on a Thursday or gives better MPG when there’s a ‘Y’ in the month. This is just a pile of bunkum put out by manufactures like Solatube trying to muddy the water. Read the independent BRE test summary of Solarspot D-38 and Solatube 290DS
What does 99.7% reflective mean and how does it compare to other systems?
All solar tube type systems use ‘reflective’ tubing to transfer the light at the top to the room below. The reflectivity of the tube is one of the factors that will determine how much of that light is transferred, or lost through absorption. All Solarspot systems employ our Vegalux 99.7% reflective tubing – the most reflective material in the world. This compares with the majority of other sun pipe systems that employ either 98% or even 95% reflective tubing. Whilst this might not sound like it makes a great deal of difference there is another factor that has a big effect on the way light is bounced through the tube. With Vegalux 99.7% tubing all of the reflective value is what is known a specular. This means that as light bounces of its surface only 0.3% of the energy (light) is lost, leaving 99.7% to carry on to the next bounce. With a 98% (or less) reflective material around 5% of this reflectivity is diffuse which results in a light loss of nearer 6% per bounce. Over a relatively short distance this 6% loss per bounce quickly results in much of the light entering the top of the tube being absorbed before it can reach the room below. For more information see Vegalux tubing
How do flexible-duct sun tunnels compare to rigid systems?
The simple answer is that they don’t. In independent tests done at the BRE, where they tested two flexible duct systems (Velux Sun Tunnel and SolaSkylights Sky tunnel) the performance was shown to be so poor that even a mediocre rigid solar tube system will give around 10 times the amount of daylight. Comparing the Solarspot D-38 with the best 350 – 400mm diameter flexible system available, the D-38 will give you around 17 times more daylight.
Does the tube need to be a certain length to work?
There is no minimum length for the tube so even on the shortest systems, flat roof and vaulted ceilings, the tube will work perfectly. In fact, the simple rule is; the shorter, the better as light loss only increases as the tube gets longer.
Can Vegalux tubing be cut?
Due to the modular nature of the Solarspot system it is extremely unlikely that you would ever need to cut the tube. The design of the system allows the tube sections to ‘telescope’ into each other to adapt to the space available. In the unlikely event that you did need to cut a tube down it is relatively straightforward using a pair of aviation snips (tin snips).
Can I control the amount of daylight entering the tube?
In most situations you will want your solar tube system to deliver the maximum amount of daylight but there are certain situations where you might also control the amount of light. If you are fitting a sun pipe system in a bedroom or conference room you can vary the amount of daylight entering by fitting a Solarspot electric daylight damper. For details see our accessories page.