Introduction
Light can be studied on many different levels by different people. As architects, we will be able to give form to buildings through different lighting techniques, all are defined under the artificial and natural types.
Although artificial light has given architects and designers new opportunities to define their forms, architecture had evolved for thousands of years in response to the contribution of light from the sun. Even more importantly, humans and animals have evolved for hundreds of thousands of years with influence from the sun, their main source of energy.
The human eye has accustomed itself to solar illumination and has adapted the way it reacts to it in order to get the most from it. Not surprisingly, artificial light will have to go a long way to match up with its natural counterpart. It has been shown that, in some instances, artificial light has to produce twice the illumination that sunlight does in order to be as efficient for certain tasks.
Also, daylighting can reduce the energy consumption of a building substantialy if understood correctly. For instance, electric lights account for approximately 20-25% of the total electrical energy use in the U.S. Indirectly, the heat produced from these electric lights have an impact on cooling equipment. Apparently, as a rule of thumb, each unit of electric light contributes to an additionnal1/2 unit of electricity for space conditioning.
In order to study daylighting as an architectural tool, my research was structured in the following manner:
1 The benefits and disadvantages of daylighting
2 Certain design strategies
3 Prediction methods of daylighting
1
benefits
-human eye evolved in response to
sunlight
-gives us a sense of time...seeing
sunlight travel through a building
-less sunlight is necessary compared
to artificial light
-sustainable energy
disadvantages
-can alter certain materials...paper,
plastics, woods
-too much heat gain
-glare
-dangers of radiation
2
The increase of perimeter daylight
zones
-Allow daylight penetration high in a
space
-The effective aperture
-Reflect daylight within a space to
increase room brightness
-Slope ceilings to direct more light
into a space
-Avoid direct beam daylight on
critical visual tasks
-The emissivity of different glasses
3
-A typical lumen method
-Sun angles at 45 degrees latitude
Some design strategies
1 The increase of perimeter daylight zones
fig.1
2 Allow daylight penetration high in a space
3 The idea of "effective Aperture" for initial estimates of the optimum glazing area - product of window-to-wall ratio and the visible transmittance of the glazing is 0.18
4 Reflect daylight within a space to increase room brightness
fig,4
5 Slope ceilings to direct more light into a space
fig.5
6 Avoid direct beam daylight on critical visual tasks
fig.6
Emissivity of glasses
In order to control the amount, quality or type of natural light coming into a building, the performance properties of certain types of glasses can be altered.
The effectiveness of these glasses depend on a good combination of the different properties.
A first method is to use tinted glazings.These glazings use heat absorbing materials to reduce the amount of solar radiation passing through the glass while also reducing the amount of visible light. Depending on your design parameters, the two factors can be manipulated to meet the building's needs.
Color becomes the first variable to take into account.
"Gray glasses will reduce both light and heat at a fairly constant rate."
"Bronze glasses will reduce more light energy than heat energy."
"Blue-green glasses will reduce heat energy while still maintaining a fairly high visible light transmittance"
See fig.10
Another method of controling the natural light is the application of metallic coatings on glazings. However, these coatings dramatically reduce both light and heat transmittance because of direct reflection. Their use in daylioghting is therefore limited.
"Low-emissivity ,or "low-e", coatings are transparent to the visible light range of the electromagnetic spectrum but are reflective to most long-wave infrared heat radiation"
"Sputtered, or "soft-coat", low-e coatings can be manipulated to transmit or reflect selective ranges of the electromagnetic radiation spectrum and, as a result, can be adjusted for optimum performance in any given climate. One disadvantage of the coating is that it must be applied to one of the inner surfaces of a dual-paned glazing unit to protect the thin layer of metallic particles". They can also be applied to thin plastic films that you suspend between two layers of glass creating an extra layer of gas in the window and lowering its conductivity
Performance characteristics of Visteon
Versalux tinted glass insulated with Low-E
at---
"Pyrolitic or "hard-coat", low-e coatings are fused to the glass while it is still hot to create an integral film that is extremely resistant to abrasion and corrosion.The coatings can be used for single-pane application, but they offer inherently less variety in thermal and optical characteristics because the deposition process allows less control than the sputtering process."
Multipaned glazing has become a standard in our climate. We know the double-pane quite well but are less inclined to use the triple-pane. One reason is the price of the windows themselves, but we also have to take into account the extra weight that numerous panes add on. These can be replaced by using suspended low-e films because the thickness, weight and costs are much lower.
Other solutions are the gas fills that are commonly used. The air between panes is replaced by argon, krypton, and sulfur hexafluoride which are less conductive than air. However, one has to ask whether the process used to produce or even recycle these has an important impact on the environment
Windows are part of what we call sidelighting strategies. Another strategy is toplighting. This provides the opportunity to illuminate a space completely differently than with windows. Its effects range from a uniform light to a more dramatic and strategic lighting of certain spaces.
One disadvantage of toplighting is the access to it. In order to control the light coming in, one has to have access to the aperture itself. Another disadvantage is the fact that toplighting usually effects only the uppermost levels (lightwells can be utilized to bring light to lower ones).
Skylights are simply defined as "horizontal glazed roof apertures that are parallel to the roof"
fig.9
Large skylights are usually the most economical to install but produce a situation where it is harder to control light coming in. Smaller more tightly spaced skylights are more costly to install but tend to give more uniform light and greater energy savings.
"The general rule of thumb is to Space skylights at 1.0 to 1.5 times the ceiling height."
Roof monitors: raised sections of a roof with vertical or sloped apertures on one or more sides. They require special architectural attention because of drainage details and constuction coordination. However, they do not generate an important heat gain while allowing the upper levels to benefit from natural light.
Core Daylighting
fig.8
Core daylighting is a process that brings sunlight inside a building though different "indirect" strategies. One of the oldest examples is that of the Egyptian cultures that managed to bring light deep inside their pharaohs' tombs with a system of mirrors. The modern versions are not that different, in principle.
There are generally three aspects to core daylighting;
the light collection system;
active or passive
the light transportation system;
the light distribution system
A method for predicting interior daylighting.
fig.7
A typical lumen method
The figure shows a typical lumen method illuminance curve as a function of solar altitude used to provide an indication of the illumination that may be expected for a particular sky, solar altitude, and building orientation. It should be kept in mind that these charts provide only very approximate illumination levels, and their use should be replaced in the event that more accurate local data are available.
References/bibliography
Ander,Gregg D., Daylighting performance and design, Van Nostrand Reinhold, Toronto, 1995
Schmitz-Gunther, THomas (sous la direction de), Eco-Logis:la maison a vivre, Konemann, Cologne, 1999
Yeang, Ken, The Green Skyscraper, Prestel, New York, 1999
Pieter Sijpkes' Passive solar design web pages, u2 studio:
http: