OMI term 2 photometry

Question 1

radiometry

Answer 1

measurement of optical radiation in part of em spectrum

Question 2

photometry

Answer 2

measurement of the part of em spectrum thats detectable by human eye

Question 3

what is 1 radian

Answer 3

57.3 degress

Question 4

1 pi radian is?

Answer 4

180 degrees

Question 5

solid angle

Answer 5

measure of amount of fov for some particular point that a given object covers

Question 6

in 2d circle what is planar angle

Answer 6

ration of length of arc(c) to radius of arc (R)

thoeta equals c/R

Question 7

in 3d sphere wha is solid angle

Answer 7

ratio of area to square of radius of sphere

w=A/R Squared

Question 8

wha is solid angle measure in

Answer 8

steradians (sr)

Question 9

wha is luminuous flux

Answer 9

percieved power in all directions

Question 10

wha is luminous intensity

Answer 10

power to emit light in a given direction

Question 11

wha is illuminance

Answer 11

luminous flux density on a surface

Question 12

wha is luminance

Answer 12

intensity of light emitted in a given direction per projected area

Question 13

how to work out luminous flux

Answer 13

luminous intensity x solid angle

measured in Lumen (lm)

Question 14

how to work out luminious intensity

Answer 14

luminous flux/solid angle

measure in candela (cd)

1 candela is 1 lumen per steradian

Question 15

how to work out illuminance (E)

Answer 15

luminous intensity/ distance squared

measured in lux (lx)

1 lux is 1lm/m^-2

Question 16

how to work out luminance

Answer 16

luminous intensity/size of area

measured in candela per square metre

Question 17

what is the purpose of lighting

Answer 17

• aid and facilitate performance of visual task
• produce appropriate visual environment
• provide safe and secure environment

Question 18

inverse square law of illumination

Answer 18

as we increase distnace from light source the illumination decreases
E=I/d^2

Question 19

cosine square law of illuminance

Answer 19

as u increase the angle away from surface u reduce illumination

E=I cosA/d^2

Question 20

what happens to visual performance as illumination increases

Answer 20

it increases until reaches plateau

Question 21

name 3 types of lighting schemes

Answer 21

general lighting

local lighting

localised lighting

Question 22

general lighting schem

Answer 22

regular array of light fittings arranged to give overall illuminance in room

lights parallel lines

monotonous and flat little shadows appear unnatural

can be considered uneconomic as little used areas are illuminated to same level as highly used areas

Question 23

localised lightings schemes

Answer 23

the furnishings or work space is fixed but not regular

Question 24

local lighting schmes

Answer 24

not equal illumination

additional light may be used in area which needs it most

flexible in tha light sources may be moved around to needs of user of room

Question 25

home lighting

Answer 25

knowing nature of lighting in home enables you to give patient lighting advice with respects to task

typical room wall and ceilings light illuminate room but light decreases away from light by inverse square law of illumination

use of local light for visual performance is useful in elderly and low vision patients

Question 26

what is colour temp

Answer 26

colour appearance of light that comes from light source

Question 27

what is low colour temp

Answer 27

corresponds to warm (2700K)

Question 28

High colour temp?

Answer 28

cool (4100k)

Question 29

what gives neeutral white light

Answer 29

fluerescent lamps operating at 3500k

Question 30

what is colour rendering

Answer 30

ability of light source to represent colour in object

Question 31

if colour rendering index increases (cri) what happens

Answer 31

objects appear closer to natural colour of object and more vibrant

cri>70

Question 32

where is CRI used

Answer 32

n retail where merchandise must look appealing