LIGHTING AND GLARE CONTROL

Question 1

What is photometry?

Answer 1

This measures part of the radiant power perceived by the human eye as light

Question 2

What is Radiometry?

Answer 2

Measures the entire radiant power and the quantities derived from it

Question 3

What is luminous efficacy (lm/W)?

Answer 3

Type of way that illumination is measured
- Ratio of luminous flux to radiant flux
The ratio of light emitted by the light source within visible spectrum

Question 4

What is luminous intensity (Candela cd)?

Answer 4

Type of way illumination is measured
- Perceived power emitted by light source in a particular direction per unit solid angle
Amount of light emitted or reflected from a particular area

Question 5

What is illuminance (lux lx)?

Answer 5

• Total luminous flux incident on surface, per unit area
  Amount of light falling on object or surface

Question 6

What is inverse square of the distance law?

Answer 6

Light intensity decreases with the square of the distance to the source

Question 7

What is Lambert’s Cosine Law of Illumination?

Answer 7

Light source is not perpendicular to the task surface = illuminance reduced by cosine of the angle with perpendicular plane

Question 8

Why is light source important in low vision?

Answer 8

People aged 60 years need three times more light to achieve best VA than those in 20s

Question 9

How can natural light be beneficial?

Answer 9

It needs to be controlled and possible ways to do this are:
- Keep windows clean
- Keep curtains
- Tinting of windows/blinds/curtains
- Work with back to window

Question 10

How does artificial light help?

Answer 10

• Helps to provide adequate amount of light and look appropriate
• Increase number of lights to give more even spread of illumination
• Add wall, table or floor lights in dark areas

Question 11

What does direct artificial light do?

Answer 11

Directed to work efficiently with low light loss e.g. downlights

Question 12

What does semi-direct artificial light do?

Answer 12

60-90% of the light is emitted directly to the work area e.g. surface fluorescent

Question 13

What does indirect artificial light do?

Answer 13

Reflected from the ceiling and walls (poor efficiency) e.e. pelmet lighting

Question 14

What is diffuse artificial lighting?

Answer 14

Light diffused with soft shadows e.g. opal glass or a sphere pendant

Question 15

What are unwanted reflections?

Answer 15

• High luminance reflections which overlay the detail of the task
• Usually reduce contrast and cause discomfort

Question 16

What are the management strategies for unwanted reflections?

Answer 16

• change relative position of task and lighting/windows
• use additional task lighting to ‘swamp’ the veiling reflections
• screen the task
• screen the source (e.g. window, light)
• Avoid glossy surfaces
• Use a non-reflective screen

Question 17

What is discomfort glare?

Answer 17

-

Question 18

What is discomfort glare?

Answer 18

• A function of luminance of source, luminance of background, angular size of source and source displacement from the eye

Question 19

What can discomfort glare be reduced by?

Answer 19

• reducing luminance of source (most effective)
• reducing apparent size of source
  -increasing background luminance in line of sight
• removing glare source from line of sight

Question 20

What does a tint do?

Answer 20

• Can reduce both disability and discomfort glare
• can enhance contrast
• can alter colour perception

Question 21

How do tints work?

Answer 21

• To reduce disability glare, the tint needs to absorb light that is scattered in the eye, whilst ensuring the unscattered light is not reduced

Question 22

What does a neutral grey tint do?

Answer 22

Will reduce all light hence not change the contrast of the image

Question 23

What do blue and red lights do?

Answer 23

Blue light is scattered more than red light by the lens and it is also thought to be more harmful to the macula