Objectives

• Learn about daylighting

• Review lighting - terminology- technology- design

Review of zonal cavity designmethod

• Calculate CU

• Calculate number of fixtures need for a specific space

• Do not ignore S/MH ration when you distribute lamps

Terminology and technology

• Numerical Example:• Measurements from the previous class

Find • Luminous flux F [lm] • Luminous Intensity I [cd]• Efficacy EF [lm/W]• Coefficient of utilization (CU) for each of the three lamps/fixture

assuming that working area is 0.5m x 0.5m below the lamp• Illuminance per W of electric energy (E/P)

Solution on the whiteboard

Lamp Incandescent Fluorescent LED

Electric power [W] 59 12 8

illuminance E [lux] at distance l = 0.5m 760 lux 880 lux 1100 lux

Lamp surface temperature °C 103 89 43

Photometrics

• Luminous intensity [candela, cd] • Define the ability of light source to generate light (illumination) in

given direction

• Power – luminous flux [lumen, lm] • Quantity of light

• Illuminance – light power density [foot-candela, fc] [lux, lx] SI units

• Density of light (illumination) incident on a surface

• Luminance - surface brightness [foot-lambert, lm/ft2] • directional emission of visible light

Relation

between:

1) Luminous

intensity [cd]

and

2) Illuminance [fc]

fc = cd / distance2

Units and conversion• 1 cd = Area of unit sphere = 4·π = 12.57 lumens

Luminous flux [lumen]= Luminous intensity [cd] · (4·π)

• Luminance [Foot-lambert] = lumen/ft2 from surface in the direction of view

– define the brightness of surface – important for contrast

r=1

1cd

Daylighting computer simulation

Radiosity method

What about lighting quality?

• Zonal cavity calculations focus on light quantity

• Quality can not be ignored• CRI, evenness of illumination, transition between

light and dark, flicker, glare, color temperature

• Quality is very important

Daylighting

• Scientific and psychological studies have found:• People prefer buildings where changes in sunlight

exterior affect interior lighting• Properly lit spaces are preferred to underlit or

overlit spaces• Diffuse lighting is preferred to direct lighting• North sky lighting is ~universally preferred

What are problems with daylighting?

• Can require extensive controls

• Requires extra hardware to avoid direct lighting

• Can require expensive glazing

• Can damage works of art

• Need to limit the amount of heat associated with solar gains

Strategies for Daylighting

• Orient your building on an East-West axis

• Limit direct sunlight with exterior shades, light shelves, clerestory windows, translucent glazing

• Control glazing and conventional lighting with controls• Occupancy sensors

• Automatic blinds

• Light-level sensors

Reading Assignment

Tao and Janis

Chapter 16 and section 17.1, 17.2, and 17.4

Project 2

Measurement and analysis of environmental parameters

a) Lighting - Measurements- Calculation

b) Thermal comfort in ECJ classroom c) Noise measurement d) Report e) Daily oscillation measurement (HOBO)