Daylight is the ideal light source, both in terms of quality and energy use. A single skylight provides as much light as a dozen or more light bulbs, and the light quality is unsurpassed. Many people feel that exposure to natural daylight is conducive to good health. But one also must adjust electric lighting based on solar input and control heat loss/gain.
Skylights - Lets in light
The above picture shows you an application of skylights in Wal-Mart. As a matter of fact, Wal-Mart is doing quite a bit with skylight/dimming system:
- Every facility Wal-Mart builds today from the ground up includes a skylight/dimming system. As daylight increases, skylights allow Wal-Mart to dim the lights, or even turn them off, thereby reducing the demand for electricity during peak hours.
- Nationwide, there are nearly 600 Wal-Mart Supercenters, SAM'S CLUBS and Neighborhood Markets with this system, resulting in an annual savings of about 250 million kWh a year, enough to power approximately 23,000 homes.
- No other big box or national retailer has a similar Daylighting system. Other stores may turn off some lights, but only Wal-Mart automatically dims all of the lights as the daylight contribution increases.
- Based on an in-house study completed in 1998, Wal-Mart found that its daylighting system utilized about 25 to 35 percent less than other big box competitors.
Skylights and windows have to be designed carefully so they don't contribute to overheating. The potential for overheating from skylights will vary, depending on the orientation of your house and direction your window is facing. In northern hemisphere, south-facing windows with large overhang (as shown below) allows daylight come through but minimizes overheat in the summer. In the winter, these overhang will not block sunlight due to more slanted angle of sunlight so that the building could still harvest passive solar energy for space heating. In Sunridge Middle School at Pendleton Oregon (as shown below), the entire south-facing wall is practically all windows with green-colored overhang! South-facing skylights on relatively steep roofs will generally not lead to overheating because the sun never shines directly down onto them. Skylights placed elsewhere may need some exterior shading placed over them in the summer. Greenhouse shading material is commonly used for this purpose.
A solar tube is a small clear dome on the roof that allows sunlight to enter a highly reflective tube that guides sunshine to ceiling. A translucent diffuser lens gently disperses natural light throughout a room. Compared to a skylight, a solar tube results in less heat loss/gain, less roof penetration and construction work to install.
The following video shows the amount of energy savings from solar tubes, typical applications in a residential home and how to install a solar tube!
Hybrid Fiber Optic Lighting
The following video explains how hybrid fiber optic lighting works and the typical amount of energy it uses.
As you see in the above video, fiber optic wire connects solar collector to in-room light fixture. Combined with existing electric lighting, hybrid solar lighting delivers the benefits of the natural lighting with the convenience and reliability of artificial light!
If we compare a lighting fixture to a shower head, then the lumen output is the rate of flow of water and illuminance is the amount of water collected in a bucket at a given time. The key point is that the same total flux can give different amounts of water in the bucket, simply by moving the bucket, or by changing the spray pattern or by changing any physical obstructions between the source and the bucket. Total flux doesn't specify how much illuminance will be provided where it's needed. This is true, in part, because the luminaire, reflectors, lenses and other optical media can greatly affect the flow of light from the source to the surface of interest. Failure to remember this is a frequent cause of poor lighting design, especially in retrofit applications.
For example, the picture on the left shows an incandescent lamp on the left being replaced by a compact fluorescent lamp on the right. Here, a wide adapter ballast is used. The ballast blocks out most of the direct light from the lamp to the work surface. The distributions of light are completely different in the two cases. The result is significantly less illumination on the work surface than what one might expect from comparisons of total lumen output. Thus, lighting distribution is an important parameter for the performance of lighting systems.
The picture below is an example of efficient light distribution to the workstation. Notice the design of the fixture/reflector allows most of light be focused on the mailboxes as opposed to distributed to the ceiling.
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