Lighting Flashcards
Why do we see a wall surface as blue?
White light shines on the wall, and all of the wavelengths except the blue are absorbed by the wall.
Transmitted light
Passes through a material; the image/material is transparent.
Refraction
When a transparent image changes the image, like lenses on a pair of glasses. Occurs with mostly all transparent images. Example: a fishing line in water…looks bent/curved.
Translucent
No image at all is transmitted but there is still light passing through the material. Example, frosted glass.
Reflective; If the reflective image is maintained like a mirror what is it called?; If the image is not maintained like a glossy finish what is it called? If absolutely no light passes through the material, what is it called?
When light bounces off the material; secular; diffused; opaque (all light is either reflected or absorbed, or both)
Direct light
the kind of light that comes directly from the sun on a sunny day, very sharp shadows, and the light is very strong. ( lamp or projector light) mostly for task lighting
Diffused light
Better for flat surfaces, such as murals, painting, etc prevents veiling reflections, or reflected glare
Color Rendition Index (CRI); rating #s
How well light actually shows true color, mostly used in artificial lighting. Best possible rating is 100 (no colors missing)
Power; What is the unit measure of power?
The amount of light put out by a source, the unit of measure for the intensity of a source is the amount of light coming from a single candle, called one candlepower (cp)
Flux (F)
One foot square at a distance of one foot from a one candlepower source, the amount of light flowing through that square would be termed as one lumen (I), this flow through a theoretical surface is called flux (F).
Illumination (E)
To place a candle one foot from a blackboard there would be one lumen arriving on one squaure foot of blackboard surface, called illumination (E). the value would be called one footcandle (fc).
E = F (flux) / Area
Luminance
The amount of light leaving the surface of the blackboard would depend on its reflectivity and would give us a measure of how bright it looked which is luminance.
Inverse square law of lighting calculation
simple: if the light is a point (candle, bulb,) the flux and illumination is inversely proportional to the square of the distance from the surface.
example:
E (illumination) = I (intensity) / d2 (distance)
E = 1,600 fc / (10ft)2 = 16fc
E = 1,600 fc / (20ft)2 = 4fc
3 general categories of light
incandescent, flourescent, and high intensity discharge
Incandescent
Contains filament, usually a tungsten alloy which is heated by passing an electric current through it, it glows and gives off light and a significant amount of heat. The output of ligiht is usually warmer than the sunlight or daylight: rich in yellows, reds, and week in greens and blues.
Because so much energy is wasted in the production of heat, incandescent light is the LEAST EFFICIENT type of artifical light and short lifetime for individual bulb
Output = 15 to 18 lumens is common
Tungsten - halogen lamps
Incandescent lamps that house the filament within an inner quartz envelope and it can tolerate high operating temperatures. Also contains a special halogen gas that prevents the evaporated metal from the filament from depositing an inner surface of the quartz, resulting the filament to produce higher temperature with more light, better color, and longer life.
Flourescent Lighting
Efficient system based on passing a currenet through gaases inside a gas tube. It releases energy in the form of free electrons and gas ions. The tube is lined with phosphors which in turn are excited by the ions which result in glow of colors. Ballast, w hich ontrol voltage, can be a little noisy. Better color = higher cost warm white deluxe and royal white have best CRI. THe lifetiem depends on how many hours its lite and how many times its switched on and off.
High Intensity Discharge
4 kinds and list from least efficient to most efficient
Consisit of a lamp with in a lamp, run at a very high voltage
4 geneal types but only 3 used in architectural lighting:
1. Mercury vapor - produce very bright clear bluish light (makes humans look unhealthy), add phosphers to better the color of light (murcury vapor deluxe); lifetime 24,000 hour range output is 50 lumens per watt.
2. Metal Halide Gas - (next improvement) oidine in the inner envelope, shifts color and improves the efficacy to 80 lumnes per watt but drops lifespan to 10,000 hours.
3. High Pressure Sodium (HPS) - it develops up to 110 lumens per watt and has a 24,000 hour lifespan, color isnt that great but can uses ‘delux’ models for better color
4. Low Pressure Sodium (LPS) - lamps have the highest ranges in both lifetime and efficacy, but produce a monochromatic yellow light siutable for security lighting, since there is not color rendition at all. Everything is seen as if it where black and white.
List lamp types from least efficient to most efficient
normal incandescent
tungsten halogen, light improvement
mercury vapor
fourescent and metal halide is a tie
most efficient - high pressure sodium
low pressure sodium even most efficient but only used for sercurity lighting or similar applications
Daylighting is a __________ light?
Precaustions for sunlight during seasons.
Diffused light and perfect color rendition
Direct sunlight should be sheilded - diffused by diffused glass or bouncing off of diffused surfaces
HORIZONTAL surface gets MORE sunlight in the SUMMER and LESS in the WINTER
Daylighting techniques
- Overhang, fins
- Sawtooth skylight design facing north for illlumination, not south for solar heat gain
- Interior window shading devices
- Light shelves that permit the daylight to reflect off the ceiling and penetrate farther into the interior wihtout affecting views outside
High Efficient light fixtures
use flourescent of HID - they provide more illumination per watt
fixtures that diffuse or bounce the illumination off the ceilings or internal reflectors and cause less glare
fixtures that have higher T-8 flourescent bulbs , which produce more lumens per watt and and dimish the heat generated by the bulb
dimming features, sensor occupancy
sulfur lightingg (exterior), HID and Flourescent
LED for exit signage - last longer and cheaper to operate
Lumen Method
- developed in USA, also called Flux method
- approved by IES and long promoted by Libbey Owns Forrd as a public service
- used in clear and partly cloudy skies
- amount of daylight calculated in 3 locations 5 ft from location, middle, and 5 ft from back of room
Graphic Daylighting Design Method
(GDDM)
- calculates daylight factor contours within a room rather than individaul daylight factors at specific points
- can calculate the amount of daylight at any lcoation in the room, including the effect of corner window
- developed in Europe, assumes overcast or diffuse sky conditions. this method sanctioned by the Commission International d’Eclairage and often used in computer programs
Emergency and Exit Lighting
- most buildng codes require special emergency lighting at extis and for certain functions
- emergency lighting may be provided by a seperate generator
- most code do not allow lead acid battery packs becuase of the fumes emitted
- nickel cadmium batteries are more expensive but they are rechargable and emit no noxious fumes
- for flourescent emergency lighting, some kind of transformer and inverter are necessary.
- Use flourescent, HID sulfur lighting for exterior ONLY
- always be illuminated by at least 2 sources the general illumination and an internal or special illumination, exit signs should be visible to escaping occupants
- LED (light emitting diode) lighting for exit signs (lasts longer than cheaper than incandescent)
Daylight Factor
ratio of indoor illuminance to available outdoor illuminance
daylight factor = 0.2 x (window area / floor area)
Efficacy
The amount of light produced vs the power input
(lumens vs watts)
Energy Policy Act
set minimum standards for energy efficiency on incandescent and flourescent lighting
luminare
a complete light fixture including lamps
Effective Aperature (EA)
product of visible transmittance multiplied by the window to wall ratio. An EA of .20 to .30 provides good daylighting
Bilateral Lighting
- daylight lighting coming from 2 sides to illuminate a space
- generally most evenly distributed when bilateral lighting from opposite walls is used
Foot Candle
- the illuminance cast on a surface by a one-candela source one foot away
- Light Pollution: Brightening of the night sky that inhibits the observation of stars and planets, caused by street lights and other man-made sources
Footcandle Levels and Recommendations
Sunlight=10,000 fc
Full Daylight=1,000 fc
Overcast Day=100 fc
Very Dark Day=10 fc
Twilight=1 fc
Full Moon=0.01 fc
Public Spaces with Dark surroundings=2-5 fc
Simple orientation for short visits=5 – 10 fc
Houses, Warehouses, Theaters=150 fc
Offices, Libraries, Grocery, Labs=500 fc
Office Landscapes=750 fc
Fixtures that use _____ or ___lamps provide more illumination per watt than ____.
fixtrures that have higher efficienty ___ ___ bulbs produce more lumens per watt and diminish the heat generate by lighting.
always use high efficiency electronic ___
flourescent or HID
incandescent
t-8 Flourescent
ballasts
Use fixtures that diffuse light or bounce the illumination off the ceilings or internal reflectors which are more efficient because?
cause less glare with computers and save operating costs
Low Pressure Sodium
- used only for areas of safety/security and street lighting
