Chapter 8 Quantity of Lighting © 2006 Fairchild Publications, Inc.

Definition of terms Rules of thumb Precise calculations

Measurement terminology 2 4 1 3 5

1: Luminous intensity: light flow in a particular direction

2: Luminous flux: total output

Lumen The quantity of light falling on a one square foot area illuminated to one foot-candle

3: Illuminance: density of light landing on a surface, in Lumens per square foot (“foot-candles”)

Adjusting the target numbers Task proper: 67-133% Immediate surroundings: 33-100% Surroundings: 10-100%

5: Luminous exitance: light reflected from (or passed through) a surface

Inverse square law

Illumination level over distance

Good for initial layout Rules of thumb Good for initial layout

Recessed downlighting

Recessed wall washers ¼ height of wall space the same distance as they are from the wall Always check mfr

Fluorescent downlight layout Determine spacing you want – will depend on the grid you use and the fixture output

Spot lighting

Precise calculations Good for final layout Use where levels are important Point source for specific locations (paintings, sculptures, tasks) Whole room calculations (more open areas)

Point calculation Footcandles=candela/distance2

So, using this lamp from 10’ away gives you how many footcandles?

What about this fixture?

Use photometric data for exact luminaire and lamp

Watts per square foot method Very rough Does not take ceiling height into account

Project: this classroom Lectures and computer use (20-50fc) 25’x45’=1125

True calculations Called the “Zonal Cavity” method Use many, many factors Room cavity ratios (RCR) Coefficient of utilization for luminaires (CU) Light loss factor (LLF) Lamp lumen depreciation (LLD) Luminaire dirt depreciation (LDD) © 2006 Fairchild Publications, Inc. Chapter 7 Quantity of Lighting

fc = Number of lamps  Initial lamp lumens  LLF  CU Basic Formula fc = Number of lamps  Initial lamp lumens  LLF  CU Area Inserted multiplication sign from Symbols © 2006 Fairchild Publications, Inc. Chapter 7 Quantity of Lighting

Recommended surface reflectances

Typical reflectances

Definition: the room cavity ratio

Using a form:

Luminaire Dirt Depreciation

Illumination gradients: what we’re looking for

Illumination gradients

Project: this classroom Lectures and computer use 25’x45’ 12’ ceilings GWB White walls

Use an online calculator Zonal cavity method Precise: based on exact luminiare

Let’s use this beauty from Philips/Lightolier

Enter project data and post result to GullNet Light loss factor Room dimensions Target FC

Row 1: Do this room Row 2: White gwb ceiling/dark wood furniture/dark painted wainscotting Row 3: This room, with 18’ ceilings

In-class exercise Measure light level on different work surfaces Use an app: Light Tester for Android LightMeter for iPhone

Another in-class exercise: Re-lamping my kitchen Replace (2) 60A19 overhead luminaire lamps Replace (6) 50PAR20 halogen downlight lamps

Process Find LED with equivalent output (means you need to find original output) Figure return on investment over life of LED (assume $0.37/bulb) – try this site

Who can save me the most? Try shopping for a cheaper lamp Consider beam spread on PAR20s

Any questions about the midterm?

Let’s meet at 2 at the Home Depot in Danvers, in the lighting section We will also go to craft store We will be looking at materials for custom luminaires