day lighting
Using
daylight in your building is a key strategy for passive design. Letting sun
into your building impacts visual comfort, as well as thermal comfort.
Understanding how light from the sun enters a building as well as how to use
the light once it is in a building are important considerations for successful
day lighting.
Like most things, daylighting has advantages and disadvantages. But by becoming skilled at understanding the technical components of daylighting, you can make sure to maximize the advantages and minimize disadvantages.
Sunlight vs. Daylight:
Because the sun is predictable, daylight can be a reliable light source.
Sunlight is considered as the light that enters a space directly from the sun. This type of light is generally not good for lighting an interior space. Direct sunlight can produce glare and excessive heat gain.
Daylight or skylight describes the desirable natural light in a space. Daylight results in a perceived even distribution of light that avoids the glare and ill effects of direct sunlight. You can use BIM software tools to help improve your daylighting strategies (see Daylighting Analysis).
Although natural light comes from the sun, you don’t want direct sun for daylighting design.
Like most things, daylighting has advantages and disadvantages. But by becoming skilled at understanding the technical components of daylighting, you can make sure to maximize the advantages and minimize disadvantages.
Sunlight vs. Daylight:
Because the sun is predictable, daylight can be a reliable light source.
Sunlight is considered as the light that enters a space directly from the sun. This type of light is generally not good for lighting an interior space. Direct sunlight can produce glare and excessive heat gain.
Daylight or skylight describes the desirable natural light in a space. Daylight results in a perceived even distribution of light that avoids the glare and ill effects of direct sunlight. You can use BIM software tools to help improve your daylighting strategies (see Daylighting Analysis).
Although natural light comes from the sun, you don’t want direct sun for daylighting design.
- Daylight is diffuse natural light from the sky. For daylighting design, you DO want daylight.
- Sunlight is direct light from the sun itself. For daylighting design, you DON’T want sunlight. It creates light that is too intense and can bring unwanted heat.
sky conditions
The
availability of daylight is dictated by the conditions of the sky at a given
point in time; which is mostly controlled by the density of cloud cover. The
International Commission On Illumination (CIE) classifies fifteen different
types of sky conditions that can be associated with noticeably different
luminance distributions.
When conducting daylighting analysis it is important to design for a range of conditions. This means making sure that you analyse a range of sky conditions, not just a bright and clear sky. It's unlikely that these conditions well be true for every hour of every day. Good analysis will consider bright and clear sky as well as an overcast sky.
When conducting daylighting analysis it is important to design for a range of conditions. This means making sure that you analyse a range of sky conditions, not just a bright and clear sky. It's unlikely that these conditions well be true for every hour of every day. Good analysis will consider bright and clear sky as well as an overcast sky.
massing & orientation for day lighting
Massing and
orientation are important design factors to consider for visual comfort, or
daylighting. Many of the strategies are similar to those for passive heating,
but also different factors, such as glare, to consider.
Massing for Visual Comfort:
It can be very difficult to get consistent daylight and control glare from east and west windows. However, the side of the building facing the sun's path (the equator-facing side) can generally be easily shaded with overhangs, light shelves, or louvers, and the side of the building facing away from the sun's path gets little or no glare.
Therefore, generally buildings that are longer on their east-west axis are better for daylighting and visual comfort.
By using skylights, single-storey buildings can easily achieve good daylighting throughout, no matter how wide they are. However, single-storey buildings are often not the best use of land. For good daylighting, larger and taller buildings should have thinner profiles to maximize daylighting potential from side windows. This also provides more opportunity for views.
Large buildings can get daylight into more spaces by having central courtyards or atria, or having other cut-outs in the building form. Increasing the height of each storey to allow for higher windows also helps pull daylight further into the building.
Orientation for Visual Comfort:
As with massing for visual comfort, buildings should usually be oriented east-west rather than north-south. This orientation lets you consistently harness daylight and control glare along the long faces of the building. It also lets you minimize glare from the rising or setting sun.
If the building has cut-outs to maximize daylighting, the orientations of these cut-outs should also be chosen to maximize north and south walls. With good building massing, such cut-outs can also act as their own shading to prevent glare.
Massing for Visual Comfort:
It can be very difficult to get consistent daylight and control glare from east and west windows. However, the side of the building facing the sun's path (the equator-facing side) can generally be easily shaded with overhangs, light shelves, or louvers, and the side of the building facing away from the sun's path gets little or no glare.
Therefore, generally buildings that are longer on their east-west axis are better for daylighting and visual comfort.
By using skylights, single-storey buildings can easily achieve good daylighting throughout, no matter how wide they are. However, single-storey buildings are often not the best use of land. For good daylighting, larger and taller buildings should have thinner profiles to maximize daylighting potential from side windows. This also provides more opportunity for views.
Large buildings can get daylight into more spaces by having central courtyards or atria, or having other cut-outs in the building form. Increasing the height of each storey to allow for higher windows also helps pull daylight further into the building.
Orientation for Visual Comfort:
As with massing for visual comfort, buildings should usually be oriented east-west rather than north-south. This orientation lets you consistently harness daylight and control glare along the long faces of the building. It also lets you minimize glare from the rising or setting sun.
If the building has cut-outs to maximize daylighting, the orientations of these cut-outs should also be chosen to maximize north and south walls. With good building massing, such cut-outs can also act as their own shading to prevent glare.
redirecting light
Redirecting
light is the use of building elements to bounce sunlight into more desirable
locations in the building. Light shelves and baffles are two strategies that
can distribute light more evenly.
Light Shelves:
To evenly distribute light, it is often desirable to bounce sunlight off of surfaces. Direct sunlight on work surfaces often causes glare. Light shelves are devices that both shade view windows from glare and bounce light upward to improve light penetration and distribution.
A light shelf is generally a horizontal element positioned above eye level that divides a window into a view area on the bottom and a daylighting area on the top. It can be external, internal, or combined and can either be integral to the building, or mounted upon the building.
Light shelves are most effective on walls facing the sun's path; on pole-facing walls they simply act as shades. Light shelves on east and west orientations may not bounce light that much further into the spaces, but are an effective means of reducing direct heat gain and glare.
Exterior light shelves reduce daylight near the window but improves the light uniformity. The recommended depth of an external light shelf is roughly equal to its height above the work plane.
To reduce cooling loads and solar gain, an exterior light shelf is the best compromise between requirements for shading and distribution of daylight. Because they are only shades, they do not change the ratio of incoming light to heat, but better distribution of light can reduce the amount needed in a space, which helps with cooling.
Light shelves may be constructed of many materials, such as wood, metal panels, glass, plastic, fabric, or acoustic ceiling materials. Considerations that affect the choice of material include structural strength, ease of maintenance, cost, and aesthetics.
Light shelves and vertical fins do not need to be opaque; when they are transparent but diffusive, they can help evenly distribute light without reducing the total amount of light significantly.
Sizing Light Shelves:
The orientation, height, position (internal, external, or both), and depth of the light shelf are critical. A rule of thumb is that the depth of the internal light shelf be approximately equal to the height of the clerestory window head above the shelf. The optimal width and placement of light shelves depends on the site's location and climate.
Baffles:
When light shelves are oriented vertically, they are known as baffles. They are used with skylights or roof monitors to better distribute daylight and avoid glare. Designing the optimal height and placement of baffles is done the same way as designing light shelves.
Light Shelves:
To evenly distribute light, it is often desirable to bounce sunlight off of surfaces. Direct sunlight on work surfaces often causes glare. Light shelves are devices that both shade view windows from glare and bounce light upward to improve light penetration and distribution.
A light shelf is generally a horizontal element positioned above eye level that divides a window into a view area on the bottom and a daylighting area on the top. It can be external, internal, or combined and can either be integral to the building, or mounted upon the building.
Light shelves are most effective on walls facing the sun's path; on pole-facing walls they simply act as shades. Light shelves on east and west orientations may not bounce light that much further into the spaces, but are an effective means of reducing direct heat gain and glare.
Exterior light shelves reduce daylight near the window but improves the light uniformity. The recommended depth of an external light shelf is roughly equal to its height above the work plane.
To reduce cooling loads and solar gain, an exterior light shelf is the best compromise between requirements for shading and distribution of daylight. Because they are only shades, they do not change the ratio of incoming light to heat, but better distribution of light can reduce the amount needed in a space, which helps with cooling.
Light shelves may be constructed of many materials, such as wood, metal panels, glass, plastic, fabric, or acoustic ceiling materials. Considerations that affect the choice of material include structural strength, ease of maintenance, cost, and aesthetics.
Light shelves and vertical fins do not need to be opaque; when they are transparent but diffusive, they can help evenly distribute light without reducing the total amount of light significantly.
Sizing Light Shelves:
The orientation, height, position (internal, external, or both), and depth of the light shelf are critical. A rule of thumb is that the depth of the internal light shelf be approximately equal to the height of the clerestory window head above the shelf. The optimal width and placement of light shelves depends on the site's location and climate.
Baffles:
When light shelves are oriented vertically, they are known as baffles. They are used with skylights or roof monitors to better distribute daylight and avoid glare. Designing the optimal height and placement of baffles is done the same way as designing light shelves.