Natural light has two main advantages over artificial lighting. Firstly, natural lighting reduces electricity bills because it is available for free. Furthermore, it offers perfect color reproduction performance, allowing the colors and textures of objects to be appreciated without visual distortion. No artificial light source can offer this combination of benefits:
- Incandescent and halogen lighting match daylight in color performance, but both types of lighting are inefficient and expensive to operate. Another disadvantage of incandescent and halogen bulbs is their short lifespan, typically less than 1,000 hours of use, which means replacements are required frequently.
- LED luminaires offer a very low operating cost, but many products do so at the expense of color performance. Some of the newer LED bulbs are designed to replicate the warm, natural color output of incandescent lighting, but this often comes at a higher price.
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LED lighting is a high-performance technology that offers significant energy and maintenance savings over its lifetime, but natural light is always the winning option when available. However, there are three important factors to consider for an effective implementation of natural lighting:
- The sun has a warming effect, and successful daylighting design should minimize it while still allowing sunlight into the building. If solar heating is left unchecked, it can significantly increase air conditioning loads, negating some of the potential savings.
- Sunlight is not available at night and is limited during cloudy days, so the building must be equipped with controls that adjust artificial lighting in response to this situation. Additionally, controls ensure that savings are achieved when natural lighting is sufficient by dimming or turning off internal luminaires.
- Natural lighting design must ensure that the sun is not directly visible to occupants, as the resulting glare is unbearable. The same applies to shiny surfaces that can reflect the sun, which also causes glare.
Natural lighting is highly recommended in commercial buildings, contributing positively to employee motivation and productivity, in addition to providing energy savings.
Optimizing Window Orientation for Natural Light
Windows play a very important role in any natural lighting project, as they must be placed in such a way that natural light can enter the building, but at the same time heat and glare must be avoided. In general, windows on the north and south sides of a building perform much better than those facing east or west.
In New York and elsewhere in the Northern Hemisphere, most of the sunlight available year-round comes from the southern portion of the sky. Therefore, south-facing windows receive the most natural light, with minimal glare and heating because the sun's elevation above the horizon is high and most sunlight is received at an acute angle. The sun is at a lower altitude in winter, increasing the heating effect, but this is beneficial because the total heating load is reduced. However, you may need to control glare with curtains. North-facing windows are also effective for natural lighting because most of the sunlight they receive throughout the year is indirect, meaning glare and heating are minimized.
East-facing windows receive direct sunlight in the morning, and so do west-facing windows in the afternoon. For effective natural lighting, the number of east- or west-facing windows should be minimized, and extensive use of shading is often necessary to avoid glare and excessive heating. In low-rise buildings, it is often possible to use trees for additional shading. If the surrounding buildings are taller, they also effectively block direct sunlight.
Glare should be avoided in all circumstances: light glare is distracting and uncomfortable, and intense glare severely limits visibility and can damage the eyes. Heating is welcome in winter, but it drastically increases air conditioning loads during summer. To achieve the best results with natural lighting, window area should be maximized on the north and south sides of a building and minimized on the east and west sides.
High-efficiency skylights and windows
Skylights and high-efficiency windows are the two most common types of daylighting products for buildings. Both are designed to maximize lighting while keeping the heating effect in check.
Skylights
Skylights allow buildings to capture heat through the roof and their geometry is designed to minimize heat transfer into the building. Skylights have greater potential in low-rise buildings with a large coverage area, where it is often possible to completely turn off the artificial lighting system. Warehouses, industrial plants and shopping centers are some examples of buildings where skylights have high potential.
Solar panels are a great complement to skylights, as they can be used to fill the gaps between them, ensuring that all the sunlight falling on the roof is used. Sunlight that is not used for natural lighting is converted into electricity and used to power other appliances, which may include artificial lighting.
The potential uses of skylights in skyscraper construction are more limited, as the roof area is small compared to the total interior area and only the upper levels can benefit from the concept.
High-Efficiency Windows
There are now fenestration products designed to allow sunlight through while blocking a significant portion of heat, and they can be effective in daylighting designs. For example, double pane windows use two sheets of glass with a space between them to minimize heat conduction. The gap can be vacuumed or filled with an inert gas for best results. Some windows also use photochromic glass, which is normally transparent but becomes more opaque in response to the amount of incident light.
A window's ability to block heat is specified by its Solar Heat Gain Coefficient (SHGC), which is a ratio of heat transmitted to heat received. For example, a high-efficiency window with a SHGC of 0.50 blocks half of all solar heat while letting most of the light through.
Internal lighting automation to complement natural lighting
The main limitation of natural light is that availability depends on the time of day and local climate. The building still requires an artificial lighting system, with the difference that it can be turned off or configured to operate at partial output when there is natural light. Capturing natural light consists of maintaining constant lighting levels, regardless of the amount of natural lighting available:
- If natural lighting can provide 100% of the illuminance level, the luminaires will be turned off.
- As the availability of natural lighting decreases, the artificial lighting output is controlled with dimmers to compensate for the gap.
- During the night, lighting requirements are fully met with artificial lighting.
It is important to note that natural lighting only provides savings if the artificial lighting system is reduced or turned off in response to natural lighting levels. If luminaires are left on all day at full brightness, indoor environments will be illuminated more than necessary and the potential savings will be negated. In fact, energy consumption can increase because the air conditioning system must remove heat from two sources simultaneously – artificial lighting and the sun.
Controlling brightness in natural lighting design
Glare problems can arise in poorly designed daylighting systems and it is important to distinguish between the two main types of glare:
- The uncomfortable glare is unbearable and causes an instinctive reaction to close your eyes and look away. This is the kind of glow you get if you accidentally look directly into the sun.
- The glare caused by the deficiency limits vision, but does not cause the drastic reaction of uncomfortable glare. An example of poor glare is when a shiny object is reflected on a computer screen and makes it difficult to read.
Proper window orientation not only limits heat gain but also controls glare. By minimizing the number of east and west facing windows and using adequate shading, glare is significantly reduced. Interior design also plays an important role in keeping glare at bay. Any surfaces or objects that can directly reflect sunlight should be avoided, especially if they reflect lights into occupied areas.
Final Observations
Natural lighting can significantly reduce electricity bills while helping to create indoor environments that feel natural and inviting. However, professional design services are highly recommended before attempting any daylighting projects, otherwise there may be issues with glare or excessive solar heating.
