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Ophthalmic Optics II Fall 2020 > Illumination > Flashcards

Illumination Flashcards

1
Q

Luminous power

-Definition and units

A

Total light power produced by a source
lumens
Essentially in all directions

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2
Q

Luminous intensity

A

Light power produced b y a source in a given direction.

Candelas (lumens/steradian)

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3
Q

Illuminance

A

The light incident on a surface. Lux (lumens/m^2)

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4
Q

Luminance

A

The light coming off a surface in a specific direction.
Measured in

foot lamberts (lumens/steradian/m^2)

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5
Q

reflectance

A

Luminance/illuminanation

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6
Q

Luminarie

A

Complete lighting unit consisting of a light source.

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7
Q

Wattage

A

The amount of electricity consumed by a light source

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8
Q

Lumens

A

The amount of light that a light source produces

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9
Q

Efficiency

A

Lumens/watts

LED&raquo_space; fluorescent&raquo_space; Incandescent

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10
Q

2 categories of light

A

Incandescent- produces light through heat

Luminescent- produces light through excitation of individual atoms.

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11
Q

Two types of Incandescent lights

A

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.

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12
Q

Incandescent light bulb pros and cons

A

pros- low initial cost, small lamps, easy to install. Great color rendering!!!!!!!!!!

cons- short life. Least efficient.

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13
Q

Types of luminescent lights

A

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!!!
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14
Q

Which type of luminescent light is used at football fields?

A

Low intensity discharge lamps

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15
Q

Which type of luminescent light is used in parking lots or tunnels?

A

Low pressure sodium lamps. Poor color discrimination. Lasts long and covers a lot of area.

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16
Q

Which type of luminescent light releases blue light?

A

LEDs

17
Q

Which type of luminescent light contains mercury?

A

Fluorescent

18
Q

Two major components of environmental lighting

A
  1. Quantity. Amount of light.

2. Quality. Color, brightness, glare, uniformity

19
Q

General lighting vs supplemental lighting

A

General

  • Luminance is direct. Efficient, has shadows.
  • Illuminance is indirect. Not efficient, no shadows.

Supplemental

  • Incandescent
  • Fluorscent
20
Q

Advantages and disadvantages for direct and indirect general lighting

A

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.

21
Q

How to determine illumination levels Based on system adopted by IESNA (Illuminating engineering society in north america)

A

Determine task characteristics
Determine the criticality of the task
Determine age of the users

22
Q

quality of illumination is based on

A

Light source characteristics

  • Color rendering
  • Color temp
  • Spectral power distribution

Glare
Uniformity of illumination
Brightness ratio

23
Q

Object color

A

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

24
Q

Color rendering

A

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.

25
Q

Correlated color temp

A

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.

26
Q

Standard illuminants: A, B and C

A

Illuminant A - Average incandescent lightbulb
illuminant B - direct sunlight at noon
illuminant C - Average daylight.

27
Q

4 types of glare

A

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.

28
Q

IESNA considers illumination to be uniform if the max and min levels are not more than __ above or below the average level

A

1/6

Tip: Closer spaced lights, paint ceiling white.

29
Q

Ideal brightness ratio

A

1:3 or 3:1

Higher ratios such as 10:1 or 40:1 are better for outdoor activities.

30
Q

When looking at luminaire types, what do you want your efficiency and CRI to be?

A

Ideal if CRI is 100% and efficiency (lumens/watt) is high.

31
Q

Which luminaire has the lowest efficiency? highest?

A

Lowest- incandescent.

Highest is Low pressure Na+ used in parking lots.

32
Q

Which luminaire has the highest CRI? lowest?

A

Highest- incandescent

Lowest- Low pressure Na+

Ophthalmic Optics II Fall 2020 (8 decks)

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