One of the great things about The Bahamas is the bright sunlight that we get to enjoy, and with advances in window technology, we have the opportunity to harvest an abundance of free natural light without the massive gain of heat into the space.

There is a lot of buzz around the use of natural light to reduce the cost of energy used to light spaces by artificial means. This is known as 'harvesting daylight'. If we consider that about 15 percent of energy costs in buildings may be attributed to lighting, finding ways to reduce this can be important with the added benefit of many persons citing natural light as more pleasing.

If we take a look back, the builders of the old clapboard houses with wooden shutters that doubled as windows were onto something. They used a piece of board to fix the shutter in the open position during the day, allowing light into the space, meanwhile the shutter provided shading which helped to keep the house cool. It's simple and it works, but the downsides are obvious. The challenge for modern buildings though is to get the same effect.

For quite some time as we built up more gentrified neighborhoods using concrete block construction, most with wooden roofs, some with concrete slabs as roofs and modern windows, we could not figure out why these spaces were so hot. No matter how hot it was outside, whether or not the windows were open, the inside was much hotter. We began using air-conditioning, and then guess what - our electricity bills soared because we were trying to cool down a very inefficient building.

One of the culprits is the type of glass being used for windows. If we just look at the glass for a moment, we see that when the glass lets in light, there is also heat added to the space mainly through transmission. Some of this can be reflected off the glass by using special applications or coatings. Heat energy may also be absorbed by the glass and transferred to the space by convection and radiation.

In the past we tended to primarily use single-glazed windows, and to help reduce heat being added to the space, an inexpensive option utilized by many store fronts was the manual application of tints, which often peeled, were prone to discoloration and restricted natural light.

Double glazed glass, which simply means there are two sheets of glass separated by a gap filled with an inert gas, gained popularity for its improved insulation resistance.

It was found that, though double glazed is better than single glazed, the performance of the glass could be further improved by the use of solar low E glass coatings, where the "E" refers to emissivity or its ability to radiate energy. So when selecting glass, you want to go with the glass with the lowest E value that fits within your budget.

All of this comes at a cost, though, so a careful analysis of the savings expected should be done. Energy savings should be realized through the combination of a reduced need for artificial lighting as well as reduced work the air-conditioning system has to do because of better insulated glass.

When selecting windows, we must look beyond shape, beauty, tint and first cost as the performance can impact the long term cost of this investment.

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