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There are a lot of important factors when choosing the right light fixture. We really care about the selections such as lumens per watt, color temperatures but how about light distribution?

The importance of distribution of light is actually in the fixture itself. With the correct distribution of light, you can lower fixture counts and get a better sustainable project. Determining a luminaire’s light distribution can be also a key consideration.

Light distribution is basically the projected pattern of light which is fixture can distribute onto a surface. Fixtures are available in wide variety of distribution patterns, from uniformly diffuse to highly directional, narrow beams.

The effect and diffusion of light vary according to the beam of light. We can collect this issue in 7 ways;





Indirect

This type of luminaire can be used to create a feeling of the height in large rooms without low ceilings. The term generally refers to light emitted in a downward direction. Troffers and downlights are two types of direct lighting luminaires.






Semi-indirect

Light reflected from the ceiling tends to soften shadows and improve brightness ratios. Luminaire brightness can be approximately equal to the brightness of the ceiling because light also is directed downward.







Direct-indirect

These luminaires provide approximately equal light to the floor and ceiling and very little light to the sides. Consequently, brightness can be low in the zone of direct glare.







Diffuse

These fixtures provide approximately equal light in all directions. To control direct glare, diffusing enclosures should be large and lamp wattage low.








Semi-direct

A small percentage of light directed upward tends to soften shadows caused by direct luminaries, like downlights. These applications are where strong light is not necessary e.g., stairways, corridors, and storage areas.




Direct; Wide Beam Spread

Direct fixtures can be used for focus and emphasis. To prevent high brightness ratios, ensure that sufficient illumination is provided on walls and other vertical surfaces.

Direct;Highly Concentrated Beam Spread Downlight

Beam spread depends on the reflector, lens, and position of lamp in luminaire.

 

Sources;

Architectural Lighting Book: Architectural Lighting by M. David Egan and Victor W. Olgyay

 

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    Daylight can be defined as diffuse light through clouds or partially cloudy skies. In a cloudy climate, the diffuse sky is often the main source of useful daylight.
 
    For climate conditions in which cloud cover exists (no visible sun for a substantial percentage of the year), we should design to optimize daylight. In this case, the light source is the sky, not the sun or sunlit surfaces. Still, some of the sunlight strategies also apply to daylight, such as using light efficiently, controlling the amount of light, and integrating with architecture. Because the overcast sky not a point source it is an area source.
 
    Here are the basic approach to the daylighting strategies;



1. Maximize solid angle of the sky seen from the task or light-reflecting surfaces. In practice, this means that tasks cannot be too far from the aperture. (windows and skylights). However apertures can be larger for daylighting than for sunlighting.

2. Shade to prevent glare. avoid direct views of overcast sky because it is a bright source of potential glare. Shading is not needed on the building exterior since heat gain is not a problem from overcast sky conditions.
 
3. Do not block light. Do not use solid light shelves or overhangs. They are not effective for redistributing light in overcast sky conditions and may reduce the amount of daylight reaching the task.

4. Locate openings high. Openings should see the brightest part of the sky. The overcast sky at the zenith is about 3 times brighter than at the horizon. High window locations and horizontal skylights will provide the best access to light
from overcast sky.

5. Shape space to minimize absorption of light. Use high-reflactance interior finishes. Maximize the ceiling height near windows to allow high windows and slope ceiling down toward the rear to minimize interior surface area.


Follow us on our next article “Planning for Solar Access ”.

Sources; Architectural Lighting by M. David Egan and Victor W. Olgyay
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