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LIGHTING DESIGN LECTURE 9 – March 22 Lighting For Tasks

LIGHTING DESIGN LECTURE 9 – March 22 Lighting For Tasks. The IES: Illuminating Engineering Society. The governing body of lighting engineering IES associates tasks with specific light levels (illuminance) To understand why, we BRIEFLY REVIEW “illuminance” source - surface - viewer diagram

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LIGHTING DESIGN LECTURE 9 – March 22 Lighting For Tasks

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  1. LIGHTING DESIGN LECTURE 9 – March 22Lighting For Tasks The IES: Illuminating Engineering Society. The governing body of lighting engineering IES associates tasks with specific light levels (illuminance) To understand why, we BRIEFLY REVIEW “illuminance” source - surface - viewer diagram We quantify light as “Lumens” Lumens (light) striking a surface Illuminance = E Measured in foot-candles “FC” Lumens (light) leaving a surface arbitrarily Exitance = M Measured in foot-lamberts “FL” Lumens (light) leaving a surface in a specific direction and density Luminance = L Measured in Candelas per Sq.Meter • All measures of light boil down to density: Lumens per area. Just like measuring rain.

  2. LIGHTING DESIGN LECTURE 9Lighting For Tasks

  3. LIGHTING DESIGN LECTURE 9Lighting For Tasks Recognize that Illuminance is light ON TO a surface Units: foot-candles Does not tell us about the appearance of the surface being lighted Does not tell us about the perceived brightness of a space So why are lighting criteria based on Illuminance? Vision is based on contrast IES is concerned with lighting for specific tasks Tasks are assumed to be of materials of known reflectances Known reflectance = known contrast Known contrast = known visual performance (old) IES considerations that affect criteria Age of participants Time allowed for task Importance of task Reflectance of surroundings • Proper task illuminance does not automatically mean a successful or bright environment.

  4. LIGHTING DESIGN LECTURE 9Lighting For Tasks (current) IES considerations that affect criteria Minimize glare Evenness Background light levels Color rendering requirements Energy requirements Controllability (dimming, instant on/off) Noise requirements Borrowing illuminance level criteria values The IES only intends for illuminance levels to be used to describe specific task surfaces. i.e. a desk, table, seating area, art. We will commandeer the use of illuminance levels. We describe the illuminance level of whole spaces to describe the “average ambient glow” of a space. Consider whether the space has an average illuminance level, versus contrasts of high and low. • Learn to intuitively describe a space in terms of a perceived ambient illuminance level.

  5. LIGHTING DESIGN LECTURE 9Lighting For Tasks Get used to common illuminance levels and what they mean in different environments Don’t rely on illuminance level recommendations that aren’t relevant to your space. Remember: we are talking about the fifth and last layer…(and easiest to engineer and remedy) Sample light levels to get used to Full moon moonlight: 0.1 FC Movie theater walk way 1.0 FC (minimum for emergency egress) Dim romantic restaurant 5.0 FC Comfortable living room 10-15 FC Residential task / study 20-35 FC Classroom/ small office 50-70 FC Excessively bright open office 70-85 FC 100+ FC … very bright for an interior space 200+ unheard of for an average E level in interior Remember: these are not recommendations. Rather, they are estimates of what you may be visualizing for each example.

  6. LIGHTING DESIGN LECTURE 9Lighting For Tasks Reading Assignment: The Architecture of Light, Chapter 20 Go over assignment project progression: Defining illuminance Levels: Lighting for Tasks

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