ENVIRONMENTAL SYSTEMS

LIGHT http://map.gsfc.nasa.gov/media/ Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 study carrel in Phillips Exeter Library; a celebration of light and of material (by L. Kahn) Kahn on Light I said that all material in nature, the mountains and the streams and the air and we, are made of Light which has been spent, and this crumpled mass called material casts a shadow, and the shadow belongs to Light. Louis Kahn Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

Kahn on Design A great building, in my opinion, must begin with the unmeasurable, must go through measurable means when it is being designed, and in the end must be unmeasurable. The only way you can build, the only way you can get the building into being, is through the measurable. You must follow the laws of nature and use quantities of brick, methods of construction, and engineering. But in the end, when the building becomes part of living, it evokes unmeasurable qualities, and the spirit of its essence takes over. Louis Kahn Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Light Conceptually radiant energy that is capable of exciting the human retina and creating a visual sensation. Illuminating Engineering Society of North America (IESNA) in short: visually-evaluated radiant energy if we can t see it it is not light Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

Light Physically As a physical quantity, light is defined in terms of its relative efficiency throughout the electromagnetic spectrum lying between approximately 380 and 780 nm. Illuminating Engineering Society of North America (IESNA) in short: radiation of wavelength 380-780 nanometers 1 nanometer = 1 10 9 m = 3.281 10 9 ft Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 www.lightsources.org/ Light Graphically radiation radiation radiation light radiation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

Light Graphically (in close-up) note this error >> infrared and ultraviolet cannot be seen and are not light roy g biv www.files.chem.vt.edu/chem-ed/light/em-spec.html Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 The Physics of Light Light sometimes acts like a wave. (otherwise, why specify wavelength in nm) Light sometimes acts like a particle. (think photons and quantum theory) Light seems to behave as a ray. (sharp shadows suggest this) Current thinking is that light can be understood by invoking the duality theory using waves when appropriate (as with diffraction) and photons/rays when appropriate (for day-to-day discussions). Fortunately, architectural design efforts need not await further resolution of this issue. Use whatever part of the theory works for you (most likely this will be thinking of light as a ray comprised of photons). Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

Basic Properties of Light Speed this is used as a physics (and sci-fi) benchmark i.e., the speed of light 299,792,458 meters per second (in a vacuum) (this converts to 186,000 miles per second) in any building situation this means that the travel of light from here to there is instantaneous (for design purposes, the transit time is zero) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Basic Properties of Light Wavelength 380 to 780 nm for a statistically average person (light is a physical phenomenon, but has been defined via human physiology) nm = nanometer nanometer = 10-9 meter light waves have very small dimensions (making small-scale physical models feasible) λ = one wavelength Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

Basic Properties of Light Energy light is a moderate quality form of energy electricity <> light <> heat it is important to distinguish between raw radiant energy (a physical property) and visual effect (a human response to this energy) they are not equivalent, as the eye is not equally responsive to all wavelengths (see bottom graph) visual response raw energy Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Terminology of Light DON T SAY visible light (this is redundant) SAY light (light is visible radiation) Light is visible, and if radiation is visible it is light just say light Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

Terminology of Light DON T SAY natural light SAY daylight (if you say natural light you imply there is also unnatural light but 500 nm is 500 nm) DO NOT SAY natural light Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Terminology of Light DON T SAY artificial light SAY electric light (or candle light ) Once produced, light is light. Its source may be very much of interest. Its spectrum (what we term color) may be of great interest. Emotional adjectives, however, are problematic. We do not talk about artificial sound, or artificial heat, or artificial electricity so avoid artificial light. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

UV and IR Radiation Ultraviolet (UV) and infrared (IR) radiation are not visible, and thus are not light. They are, however, important forms of radiation. UV: higher intensity than light, biologically active Three groupings of UV have been labeled: UVA = 315 to 400 nm (blacklight) UVB = 280 to 315 nm (skin effects) UVC = 100 to 280 nm (germicidal) IR: lower intensity than light, heat bearing Three groupings of IR have been identified: Near IR (short wavelength) = 780 to 1400 nm Mid IR = 1400 to 3000 nm Far IR (long wavelength) = 3000+ nm Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 UV, IR, and Light Graphically solar radiation includes IR, visible, and UV wavelengths Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

Materials and Light Light (or, more broadly, solar radiation) that encounters a building material may be: -- reflected (property = reflectance; symbol = rho) -- absorbed (absorbtance; alpha) -- transmitted (transmittance; tau) The law of conservation of energy demands that rho + alpha + tau = 100% [ ρ + α + τ = 1.0 ] The first law of thermodynamics rudely shakes us awake. von Baeyer Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Materials and Light Absorbtance is the conversion of radiation to heat via interaction with the atomic structure of a material Transmittance is the passage of radiation through a material; little or a lot of scattering may occur in transit Direct transmittance (occurs with transparent materials, produces a clear image) Diffuse transmittance (occurs with translucent materials, produces a distorted image) Reflectance is the rejection (redirection) of radiation at the surface of a material, with little change in radiation properties Specular reflectance (occurs with polished materials, produces a mirror-like image) Diffuse reflectance (occurs with matte materials, produces no clear image) All three effects may be selective that is, they may be wavelength dependent Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

Transmittance Examples direct (this photo shows that transmittance is selective, in this case a function of angle of incidence) diffuse (and wavelength selective) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Transmittance Examples transparent glazing (window) ^ < translucent glazing (skylight) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

Reflectance Examples specular (metal) ^ < diffuse (most materials) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Reflectance and Transmittance Coexist (along with Absorbtance) Denver International Airport: night and day Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

Changing Optical Character Same Material, Different Conditions Phoenix Central Library; Will Bruder day, dusk, night Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Measuring/Describing Light for this discussion let s assume an electric lamp (a light bulb ) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

Input Energy the energy input to the lamp is expressed in Watts (of electricity) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Measuring Input Energy multimeter >> WattStopper or Kill-A-Watt several devices can be used to measure electrical input (if needed) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

Total Light Output LUMINOUS OUTPUT expressed in lumens the lumen is the basic measure of light there is no direct lumen conversion to/from other energy units the same unit is used with both the I-P and SI systems I-P = inch-pounds (U.S.) SI = systeme international d unites (rest of the world) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Measuring Total Light Output integrating sphere >> a lamp is placed in the center of the sphere, which is lined with photosensors Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

Directional Light Output lots of output some output no output (due to base) light often does not leave a lamp equally in all directions Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Directional Light Output x lumens y lumens z lumens LUMINOUS INTENSITY lumens per steradian (also called a candela) a steradian is a threedimensional measure of angle (a cone versus a pie slice) for many lamps, light output varies from one direction to another same unit is used in both I-P and SI Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

Light Falling ON a Surface ILLUMINANCE lumens per square meter commonly called a lux 1 lm/sq m = 1 lux footcandles in I-P (1 lm/sq ft = 1 FC) 1 FC = 10.76 lux Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 Measuring Illuminance << illuminance meters >> analog digital illuminance is easily measured with relatively low-cost equipment Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16

Light LEAVING a Surface LUMINANCE lumens per steradian per square meter since a lumen/steradian equals a candela this becomes candela / square meter footlamberts in I-P Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 Measuring Luminance spot luminance meter luminance is easily measured, but the equipment is relatively expensive Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34 17

Other Measures of Light Luminous efficacy Brightness Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 35 Luminous Efficacy A measure of the effectiveness of a light source in converting energy (usually electricity) to light higher is better Units = lumens/watt Almost efficiency but not quite (because the units don t cancel) A key energy-efficiency indicator for light sources (lamps) 840 / 60 = 14 http://oee.nrcan.gc.ca/ Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 36 18

Brightness A qualitative evaluation of luminance (light leaving a surface) An opinion, an impression everyone s vote counts Has no units (unsophisticated verbal descriptions are used) Is relative, not absolute Influenced by luminance, physical adaptation of the eye, viewer experiences/expectations, color how bright are these samples? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 37 Measuring Brightness brightness >> meter Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 38 19