Illumination Flashcards
Luminous power
-Definition and units
Total light power produced by a source
lumens
Essentially in all directions
Luminous intensity
Light power produced b y a source in a given direction.
Candelas (lumens/steradian)
Illuminance
The light incident on a surface. Lux (lumens/m^2)
Luminance
The light coming off a surface in a specific direction.
Measured in
foot lamberts (lumens/steradian/m^2)
reflectance
Luminance/illuminanation
Luminarie
Complete lighting unit consisting of a light source.
Wattage
The amount of electricity consumed by a light source
Lumens
The amount of light that a light source produces
Efficiency
Lumens/watts
LED»_space; fluorescent»_space; Incandescent
2 categories of light
Incandescent- produces light through heat
Luminescent- produces light through excitation of individual atoms.
Two types of Incandescent lights
Conventional light bulbs
- 90% of energy lost to heat
- Electricity shot into tube with filament and gas. The filament is heated until it glows.
Halogen lamps
-Conventional light bulb + halogen gas. Whiter, brighter, longer lasting.
Incandescent light bulb pros and cons
pros- low initial cost, small lamps, easy to install. Great color rendering!!!!!!!!!!
cons- short life. Least efficient.
Types of luminescent lights
Fluorescent
- Tube with mercury vapor between two electrodes. Mercury atoms produce UV radiation.
- More efficient, less heat, longer life. Decent color rendering.
- Glare, reflections, flickers. Contains mercy, not good. Higher initial cost.
Low intensity discharge lamps
- Arc passes between two electrodes in pressured tube. Causes metallic additives to vaporize and release light.
- Efficient, lots of light over wide area
- Poor color rendering. Used high school stadiums.
- Ballast delay. Light will only start when it’s cool.
Low pressure sodium lamps
- Efficient, lots of light over wide area.
- Non existent color discrimination. Tunnel or parking lot. Places where you don’t need color discrimination but you NEED reliability and long life.
Light emitting diodes (LEDs)
- Chemical chip embedded in plastic capsule.
- Lasts 50 to 100 thousand hours. 5 years straight.
- Cost, dimmer than incandescent. Increased blue light exposure!!!
Which type of luminescent light is used at football fields?
Low intensity discharge lamps
Which type of luminescent light is used in parking lots or tunnels?
Low pressure sodium lamps. Poor color discrimination. Lasts long and covers a lot of area.
Which type of luminescent light releases blue light?
LEDs
Which type of luminescent light contains mercury?
Fluorescent
Two major components of environmental lighting
- Quantity. Amount of light.
2. Quality. Color, brightness, glare, uniformity
General lighting vs supplemental lighting
General
- Luminance is direct. Efficient, has shadows.
- Illuminance is indirect. Not efficient, no shadows.
Supplemental
- Incandescent
- Fluorscent
Advantages and disadvantages for direct and indirect general lighting
Direct-
Most efficient lighting system.
Prone to producing harsh shadows and marked reflections from the work surface.
Indirect-
Less efficient due to absorption from the reflecting surfaces.
provides diffuse lighting with minimal shadows and reflections.
Direct- efficient, but has shadows.
indirect- not sufficient, no shadows.
How to determine illumination levels Based on system adopted by IESNA (Illuminating engineering society in north america)
Determine task characteristics
Determine the criticality of the task
Determine age of the users
quality of illumination is based on
Light source characteristics
- Color rendering
- Color temp
- Spectral power distribution
Glare
Uniformity of illumination
Brightness ratio
Object color
The perceived or spectral color of an object based on its reflecting characteristics in combination with the characteristics of the illuminating source.
Important for jobs that require color matching
Color rendering
How natural and normal will a light source make things appear
Color rendering index (CRI) from 1-100. Incandescent lamps have a CRI of 100. 80-85 is desirable.
Correlated color temp
The measure of a lights color when the light is illuminated.
Equates to the appearance of a source to a blackbody radiator operating at the same temp.
Low CCT= power conc at longer wavelengths. Lights appear more red.
High CCT= power concentrated at higher wavelengths. Lights appear more blue.
Standard illuminants: A, B and C
Illuminant A - Average incandescent lightbulb
illuminant B - direct sunlight at noon
illuminant C - Average daylight.
4 types of glare
Distracting glare- lens reflections
Discomfort glare- Irritation or pain from light. Does not interfere with resolution. Test for discomfort glare by shielding with your hands.
Disability glare- Objects have lower contrast. Ex: watching a movie with the light on
Reflected glare- Glare off a book page or screen.
IESNA considers illumination to be uniform if the max and min levels are not more than __ above or below the average level
1/6
Tip: Closer spaced lights, paint ceiling white.
Ideal brightness ratio
1:3 or 3:1
Higher ratios such as 10:1 or 40:1 are better for outdoor activities.
When looking at luminaire types, what do you want your efficiency and CRI to be?
Ideal if CRI is 100% and efficiency (lumens/watt) is high.
Which luminaire has the lowest efficiency? highest?
Lowest- incandescent.
Highest is Low pressure Na+ used in parking lots.
Which luminaire has the highest CRI? lowest?
Highest- incandescent
Lowest- Low pressure Na+
