OMI term 2 photometry Flashcards
radiometry
measurement of optical radiation in part of em spectrum
photometry
measurement of the part of em spectrum thats detectable by human eye
what is 1 radian
57.3 degress
1 pi radian is?
180 degrees
solid angle
measure of amount of fov for some particular point that a given object covers
in 2d circle what is planar angle
ration of length of arc(c) to radius of arc (R)
thoeta equals c/R
in 3d sphere wha is solid angle
ratio of area to square of radius of sphere
w=A/R Squared
wha is solid angle measure in
steradians (sr)
wha is luminuous flux
percieved power in all directions
wha is luminous intensity
power to emit light in a given direction
wha is illuminance
luminous flux density on a surface
wha is luminance
intensity of light emitted in a given direction per projected area
how to work out luminous flux
luminous intensity x solid angle
measured in Lumen (lm)
how to work out luminious intensity
luminous flux/solid angle
measure in candela (cd)
1 candela is 1 lumen per steradian
how to work out illuminance (E)
luminous intensity/ distance squared
measured in lux (lx)
1 lux is 1lm/m^-2
how to work out luminance
luminous intensity/size of area
measured in candela per square metre
what is the purpose of lighting
- aid and facilitate performance of visual task
- produce appropriate visual environment
- provide safe and secure environment
inverse square law of illumination
as we increase distnace from light source the illumination decreases
E=I/d^2
cosine square law of illuminance
as u increase the angle away from surface u reduce illumination
E=I cosA/d^2
what happens to visual performance as illumination increases
it increases until reaches plateau
name 3 types of lighting schemes
general lighting
local lighting
localised lighting
general lighting schem
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
localised lightings schemes
the furnishings or work space is fixed but not regular
local lighting schmes
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
home lighting
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
what is colour temp
colour appearance of light that comes from light source
what is low colour temp
corresponds to warm (2700K)
High colour temp?
cool (4100k)
what gives neeutral white light
fluerescent lamps operating at 3500k
what is colour rendering
ability of light source to represent colour in object
if colour rendering index increases (cri) what happens
objects appear closer to natural colour of object and more vibrant
cri>70
where is CRI used
n retail where merchandise must look appealing
