WHAT IS LIGHT CONTROL?

Transcription

1 LIGHT CONTROL DSC 558 Spring 2011 Mike Kroelinger WHAT IS LIGHT CONTROL? Methods by which a lighting device controls distribution of light from the source. Key issues are: The characteristics of distributed light Effective utilization of distributed light 1

2 CHARACTERISITICS OF LIGHT Light travels in straight lines until it meets with some form of interference. After interference, light is either: Reflected Diffused Transmitted Absorbed Refraction & interference may also occur REFLECTION Process by which a part of light falling on a surface leaves the surface from the incident id side. Three types: Specular reflection Diffuse reflection Mixed or compound reflection 2

3 SPECULAR REFLECTION Light strikes and leaves a surface at an equal angle Angle of incidence equals angle of reflection Materials: mirrors & highly polished metals Uses: floodlight reflectors, polished & anodized metals DIFFUSE REFLECTION Characterisized by light leaving a surface in all directions. Occurs when a material has a rough surface. Materials: Brushed metals (spread reflection); Flat paints (complete diffuse reflection) Uses: Reflectors for medium spread beams in fixtures; room finishes. 3

4 MIXED OR COMPOUND REFLECTION Has both specular & diffuse reflecting characteristics. More than one definite direction of light. Materials: Porcelain enamels, high gloss paint. Uses: Reflectors for fixtures, saucer fixture shapes typically with a bare lamp, light shelf surfaces for daylighting. TRANSMISSION Refers to the passage of light through a surface. Resulting light may be modified in color, intensity, & direction depending on the material (glass, plastic) & it s characteristics (thickness, finish). Three types: direct, diffuse, mixed. 4

5 THREE TYPES OF TRANSMISSION Direct 80-90% of incident light is transmitted Clear glass window or lamp is an example Diffuse Light is spread in all directions; obscures source White prismatic glass & plastics Mixed Spectrally selective diffusion Opal glass as example REFRACTION Bending of light rays as they pass through one medium to another. Modifies the speed of light. Simple example straw in glass of water. Lighting example prismatic lens. Materials: glass & plastics. Uses: Control direction of light in glass, lenses, lamps, luminaires. 5

6 Snell s Law and Refraction Snell s Law gives the relationship between angles of incidence and refraction for a wave impinging on an interface between two media with different indices of refraction. REFRACTION 6

7 ABSORPTION All substances absorb light. Absorption can lead to lower brightness of sources. Reflectors that absorb light can reduce glare. Baffles, shades, louvers, reflectors, filters. Part of fixture or fixture accessories or part of daylight aperture. POLARIZATION Modifies light rays so they vibrate predominately in one plane. Most common example polarized sunglasses. Many lamps use polarization dichoric cool beam PAR lamp; some glass types as example. Reduces glare and flattens light. Depth perception may be reduced. 7

8 POLARIZATION INTERFERENCE Occurs when two light waves come together at different phases of vibration combine to form a single wave of light. Interference coatings are typically used as optical coatings: Window glass coatings Cameras Projector lenses Separate heat (radiation) from light (radiation). Used for selective transmission of color. 8

9 SUMMARY Light travels in straight lines until it meets with some form of interference. After interference, light is either: Reflected Diffused Transmitted Absorbedb Refraction & interference may also occur. Optics Demonstration Brightness Diffusion Reflection Specular reflector Diffuse reflector Circular reflector Elliptical reflector Parabolic reflector Refraction Prismatic refraction Refractive section Reflecting prism (total internal reflection) Glass reflector 9