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Sky lights - passive design in your home to improve energy and light efficiency

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Sky lights - passive design in your home to improve energy and light efficiency

by Megan Macpherson

Sky lights are an element of passive design in the home that can improve light quality and energy efficiency. A sky light lets in three times as much light as a vertical window, which can save the amount of thermal heat transmission through large expanses of glass. It also means that artificial lighting is needed less, therefore saving energy and money. Skylights are also great for dark or internal rooms, which are not able to usually utilise natural lighting.

There are different types of skylights depending on what kind of roof they are to be installed in, and what kind of room is below. In an attic for example, a window in the roof is usually a common light source for the room. Skylights can be combined with a shaft to carry the light down into a room with a flat ceiling. A shaft will vary the amount of light and heat transferred from the skylight. Heat may be absorbed into the walls of the shaft or into the roof. Less light will be transferred down a long shaft. Tube sky lights reflect light down a tube into the home which reduces the size of the actual skylight needed.

Skylights come in various shapes such as bubble, dome, triangular or square pyramid, or flat. The colour of the room will change the effect of the skylight. A light coloured room, such as white will reflect light and make the room brighter. A dark coloured room will contrast with the bright light coming from the skylight and may cause glare.

A large area may be lit by multiple skylights, and the spacing of these skylights affects the uniformity of light distribution. A way of working out how many metres of space are needed between skylights is to multiply the height of the room by 1.5.

To combat the effects of too much sun coming through a skylight, principles of solar control are being integrated into skylight manufacture. Some types of glazing can reject sunlight from directly above the skylight, but accept sunlight from less intense angles, closer to the horizon. This is important in a country like Australia, where the summer sun can heat up a house like an oven. An example is opal glazing which diffuses the light and solar heat gain through the skylight, but still allows adequate lighting. An alternative is to use blinds to block the light and heat emitted from a skylight during summer.

The effectiveness of a skylight is measured in terms of glazing efficacy and skylight efficacy. The glazing efficacy is also known as the light to solar gain ratio or LSG which represents how much light can penetrate the glazing and how much heat is transferred. The skylight efficacy is a combination of LSG and the effect of the well or shaft on light and heat transference.

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