SYSTEMS - LIGHTING Flashcards
Candle power
Candle power - unit of luminous intensity approx equal to horizontal light output from ordinary wax candle.
In SI system called candela
Footlambert
Footcandle
Footlambert -how much light is reflected US system, luminance
- 1 FL = 0.3183 candela / sf
- 1 candela = 12.57 lumens
- 100 foot candles striking a surface with 50% reflectance would result in luminance of 50 foot Lambert.
Footcandle (FC): the calculated amount of illumination on a surface
LIGHT: Point source - Surface Perpendicular to source: formula
E = i / d^2
illumination (footcandles) = candle power (candelas) / distance^2 (ft2)
Inverse square law
LIGHT: Point source - Surface not Perpendicular to source: formula
E = I*cos Angle / D^2
illumination = candle power* cos Angle / distance^2 (sf)
footcandles= (candelas) * cos Angle / f^2
LIGHT: Coefficient of utilization CU
Efficiency of a luminaire in a particular space. Number between zero and one.
CU is the fraction of light that reaches the work plane due to losses from absorption into surfaces
Light lost factor LLF
Number between zero and one,
fraction of total light from luminary that is lost due to a number of factors including lamp lumen depreciation LLD, which is the light loss due to the age of the lamb, and luminaire dirt depreciation LDD light loss due to accumulated dirt
efficacy formula
Efficacy =
(Luminaire Efficiency * Total Lamp Lumens * Ballast Factor) / Total Power Input
Typical indoor illuminance
10 to 100 fc
Need at least 1 footcandle at the floor for egress.
Incandescents
are inefficient and create a lot of heat but have high CRI
• Advantages:
Inexpensive, Compact, Dimmable
Typically “warmer” color than sunlight or daylight, they’re rich in yellows and reds and weak in green and blues
• Disadvantages:
• The least efficient to light the filament is wasted in the production of heat (About 90% waste!)
• Short lamp life: standard bulbs last about 700 - 1,000 hours
• Types:
• Come in various shapes with different characteristics
• Designation is a letter-number (e.g.: A-21 means shape “A” and size 21/8”)
Fluorescent lamps
require a ballast and are more efficient but have a lower CRI and don’t work well in cold temperatures
Pre Heat: supplanted by rapid start that maintains constant low current in the cathode, allowing them to start within 2 seconds
Instant Start: use a higher voltage to illuminate immediately
Ballast: supplies the proper starting and operating voltages to the lamp and limits the current
• Produces noise and heat so, “Class A” is good for quiet areas and “Class F” is acceptable for noisy areas.
Electronic Ballast: produces high frequency AC and lowers power consumption
for silent operation and ease of dimming.
Advantages:
- High efficacy (About 80 lm/W)
- Low initial cost
- Long life (about 10,000 - 20,000 hours)
- Variety of color temperatures (improving…no longer just “cool white”) • Dimmable
• For fluorescent lamps, dimming down to 40% of output is possible without substantially reducing luminous efficacy.
Disadvantages:
• More expensive than incandescent bulbs
Types:
T - Tube - Designated according to type, wattage, diameter, color, and method of starting
• eg: F32T8WW/RS = 32 watt, 8/8” tubular, warm white, rapid start
CF- Compact Fluorescent (Lamps bent into a U-shape and mounted on a base that houses a ballast, Can be screwed into incandescent luminaries)
• High Intensity Discharge (HID):
A lamp within a lamp that runs at a very high voltage
Advantages:
• High efficacy (About 80 lm/W)
Disadvantages:
- Produce light that is not flattering to human skin, so not used for commercial/ retail/residential applications
- take a while to warm up
• Types:
Mercury Vapor
Metal Halide
Ceramic Metal Halide
High-Pressure Sodium
Low-Pressure Sodium
LEDs
are efficient and last a long time but need to be kept cool and require a driver, blue and green colors appear to retreat; red and orange colors appear to advance.
zonal cavity method
calculates the light absorption values in zones
(zone between fixtures & work plane and zone between work plane & floor)
to determine the number of fixtures needed in a room.
Which of the following aspects of a lighting system will indicate the color temperature of the lamp ( absolute temperature in degrees Kelvin)?
CRI
LPW
CCT
The correct answer is C.
Correlated Color Temperature (CCT) indicates the color temperature of a lamp in degrees Kelvin.
The Color Rendering Index (CRI) is not measured in Kelvin and indicates the color shift in the objects illuminated.
Lumens Per Watt (LPW) indicates the efficacy of a lamp.
• Point Grid Method
• Point Grid Method:
- A method of calculating illumination (E) for surfaces not perpendicular to the source • Good for a single fixture or small number of fixtures
- Takes into account orientation and distance but ignores surrounding reflection
