LT1-5 Flashcards
Light enters through the ___?
Cornea
What does the retina do?
Forms the optical image
WHat are 4 factors that affect visiblilty
Size, brightness, contrast, time
poor lighting causes the eye muscles to become ___
Tired and fatigued
A good lighting system provides
the quantity, and the quality of light
Different colours are actually different ____
Wave lengths
What is coulour temperature measured in
Kelvin
Below 3000K is ______ lIght
soft, warm light
Above 4000K is ______ light
Hard, cold light
CRI stands for
Colour Rendering Index
What is a definiton of CRI
“The ability of a light source to portray the colour appearance of objects accurately when compared to a standard (reference) light source of the same colour temperature.”
Does Low -preassure sodium lighting have a really good or bad CRI
Really bad, its undefined
What is total quantity from a light source called and measured in?
Luminous flux, measured in Lumens
What is Illumination or lighting level on a surface called and measured in?
Called luminous flux density, measured in Lux
What is the device that measures lighting levels called
A photometer
What is luminous efficacy the ratio of ?
he ratio of the light output (lumens), to the power input (watts)
How many lumens in 1 watt for 100% effeciency
683 lumens per watt
What are some factors in lighting choices (6)
Area and type of environment
Type of task
Architectural and decorative requirements
Costs of operation
Availability
Environmental impact
Factors of quality of light (3)
Glare, diffusion, colour
What is a complete lighting unit called
Luminaire
Four different light sources for luminaires
Incandescent
Fluorescent
High-intensity discharge (HID)
LED
Lamps should be replaced at what % of their rated life
70%
WHy is it important to clean light fixtures
can add 30% more light…making sure ventilation is good
Why are incadecents bulbs bad
90% of energy is wasted in heat
What is the filament in a incandescent usually made out of and why
tungsten, very high melting point of 3419 degrees Celsius
Low rate of evaporation
WHat do the number on light bulb sizes mean?
The max width measured in 1/8ths of and inch
ex: 10 = Size = 10x1/8” or 1 ¼”
3 different bulb glass
Clear, diffuse, couloured
what is the normal lightbulb base called
Medium Edison bass
How many watt can a medium bass handle
7.5-300w
What is the next size up from medium bass
Mogul
Do incandescent lights draw more or less current when they are cold
More. It draws more current than when it is warm due to a low
initial filament resistance
What does LED stand for
Light emitting diode
Efficacy of led ( lumens per watt)
75-150 lumens per watt
Efficacy of incandescent ( lumens per watt)
22 lumens per watt
Advantages of LEDs
Low power consumption
• Negligible early installation failures
• Resistant to shock and vibration…no glass or filament to break
• LEDs are fully dimmable
• Available in all colours
• LEDs are cool when operating
• They are extra low-voltage
• Unwanted light does not bleed off
• Deliver directed light for increased system efficiency
No moving parts, no toxic gases, no filament to burn, break
or fail…nothing that will contaminate the environment
• Small size
• Extremely long service life (50 000 hours or more)
• Instant on/off in their operation
• Work well in cold weather….works well from -40 degrees to
185 degrees
• LEDs have an acceptable colour redering index…around 70
Disadvantages of leds
More expensive
• Very heat sensitive
• Reflectors or lenses are needed to disperse the light
