Concept

Not only does the sun provide heat but it also provides light. Duh… Yet, it is amazing how dark most homes are during the day.

Besides traditional windows there are skylights. Beware of placing skylights on south facing roofs – they admit more solar heat in the summer than in the winter because of their angle. For light it is better to have a skylight on the north facing roof. Another problem with skylights is they are large and let out a lot of heat for the amount of light they provide.

Another option is solar light tubes that have a small collector on the roof, with a highly reflective tube through the attic, and a diffuser on the ceiling. The advantage of these is that they provide significant light and allow less heat to escape.

Application

I have tried skylights and in general was not too happy with the results – more heat in the summer, even with low SHGC glazing, plus they are expensive and prone to leaks.

I am experimenting with a solar light tube by Solotube. The roof collector has a reflector to maximize light collection and it was fairly easy to install. My concern is that the tube is a bit flimsy and difficult to air seal and insulate around. I am impressed with the light they bring to the only two rooms in the house without windows – stairway and upstair hall. On the quantitative side, I’ll have to compare the light provided versus the expense and time to install, and I need to calculate the heat lost.

So, for about half the day, on average, there is adequate light to walk through those areas without the use of any energy. However, that still leaves the other half of the day… Certainly a small LED "night" light could be powered for years and years for what it cost to buy and install the solar light tubes, but I will assess the results and provide further comments at a later time.

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