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 but 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 sound much of a muchness. Actually even the difference of a few percent can make a hug difference.
Here’s why; firstly all of the reflective action of the 99.7% Vegalux material is what is known as specular. This means that all of the 100% of light that hits the surface of the material, 99.7% carries on down the tube to the next bounce – only losing 0.3% of energy (light) on each encounter. On all materials with less reflectivity, 98%, 96% etc are diffuse reflectivity. This mean that when the light hits the surface a percentage of the light scatters with the result that around 5% in lost on very bounce – that’s more than 16 times more. And that’s the point. The light doesn’t only bounce once to get down the tube.
To put that into perspective, 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 bunces will be considerably more. And if you introduce a few bends into the system, then a tube with anything less than a 99.7% specular reflective surface, the amount light delivered will be virtually non-existent.
Quite simply, Vegalux material is 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 Spactralight Infinity. The truth is that it is a material readily available from 3M but as a premium product with a corresponding price tag which is why most other sun pipe manufacturers opt of cheaper, less efficient alternatives.
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.
Unlike Vegalux tubing, where all of the reflectivity is specular, 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 2 0 bounces of light roughly 95% of the original light is lost.
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