SYSTEMS - LIGHTING Flashcards
Candle power
unit of luminous intensity approx equal to horizontal light output from ordinary wax candle. In SI system called candela
Lumen
SI derived unit of luminous flux
One lumen of luminous flux uniformly cast on 1 square foot of area creates an illuminate of 1 foot candle
Luminance
luminous flux for unit of projected area and unit solid angle leaving a surface.
Footlambert
Footcandle
Footlambert -how much light is reflected US system,
1FL is 1/π candle power / sf
or 0.3183 candela / sf
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
FC= Lumens (I) / area in sq. ft. (A)
Luminous intensity
measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle. Should not be confused with luminous flux, which is the total perceived power emitted in all directions.
LIGHT: Point source - Surface Perpendicular to source: formula
E = i / d^2
illumination (footcandles) = candle power (candelas) / distance^2 (f)
LIGHT: horixPoint source - Surface not Perpendicular to source: formula
E = I*cos Angle / D^2
illumination (footcandles) = candle power (candelas) * cos Angle / distance^2 (feet)
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
- Consists of a tungsten filament placed within a sealed bulb containing an inert gas, filament glows by passing an electric current through it
- 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
an arc of mercury is formed creating an ultraviolet light that strikes the phosphor coated bulb. Bulb fluoresces and produce a visible light
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 immediate
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
An electrical arc is struck across tungsten electrodes in a glass tube filled with gas and metals
Metals produce the light once they are heated to a point of evaporation
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
• Types:
Mercury Vapor
Metal Halide
High Pressure Sodium
Low Pressure Sodium
Light Emitting Diode (LED)
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.
