Osram HQI-E 150 W/NDL CL Technical Information download pdf (Page 17)

17

3.5

S

trobosco

p

ic effect and flicke

r

O

peration of a metal halide lamp on a ma

g

netic ballast

u

nder supply voltage with 50 Hz

f

requency results in

p

eriodic

f

luctuation o

f

the luminous

f

lux with double

the suppl

y

f

requenc

y

. When the current

f

low drops

n

ear the zero crossin

g

, the plasma also has

f

ar less

ra

di

at

i

on.

B

ut even on pass

i

n

g

t

h

e zero cross

i

n

g

, t

h

e

luminous

f

lux does not reach zero so that the

p

lasma

st

ill

h

as on-

g

o

i

n

g

ra

di

at

i

on.

The human eye reacts with di

ff

erin

g

sensitivity to

varyin

g

f

licker

f

requencies, and can,

f

or example, no

lon

g

er perceive

f

luctuations in luminous

f

lux above

100 Hz. Literature provides di

ff

erin

g

ways o

f

depictin

g

the sensitivit

y

o

f

the human e

y

e

f

or periodic luminous

f

lux

f

luctuations at various

f

requencies. Fi

g

. 17 shows

an example accordin

g

to Kelly and Hen

g

er

[

1

].

When operatin

g

at 50 Hz, the luminous

f

lux or intensity

f

luctuates with watta

g

e, i.e. with 100 Hz as shown in

Fig

. 15.

Li

terature uses var

i

ous equat

i

ons to eva

l

uate

chan

g

es in luminous intensity that can be perceived

b

y t

h

e

h

uman eye.

Fli

c

k

er

i

s eva

l

uate

d

accor

di

n

g

to

EN 50006 standard,

f

or exam

p

le, with a

f

licker

f

actor

F

1

0

as

whereb

y

m

(f

i

)

= time-de

p

endent modulation de

p

th

of

the luminous intensit

y

G

= filter curve for flicker sensitivit

y

dependin

g

on

f

licker

f

requenc

y

A

ccordin

g

to Afshar

[

2

]

, adaptin

g

the evaluation also to

short-term changes and implementation in a

f

ilter

f

o

r

a li

g

ht si

g

nal, such as in Fi

g

. 15, results in values

f

or

the

f

licker

f

actor as shown in Fig. 16. The perceptibility

t

h

r

eshold

is

assu

m

ed

t

o

be

1.

The

v

alues

i

n t

his

e

x-

amp

l

e rema

i

n

b

e

l

ow 1,

i

.e. no v

i

s

ibl

e c

h

anges can

b

e

perce

i

ve

d

i

n t

h

e

ligh

t

.

()

∑

=

i

ii

fGfmF )²

1

0

²

)

Fi

g

. 15: Luminous intensit

y

o

f

a metal halide lamp at

50

H

z c

h

o

k

e operat

i

on, s

h

own

i

n ar

bi

trar

y

un

i

t

s

Fi

g

. 16: Flicker

f

actor calculated

f

rom the luminous

i

ntensit

y

si

g

nal

f

or a metal halide lamp at 50 Hz choke

operat

i

on, s

h

own

i

n ar

bi

trar

y

un

i

ts

Fig. 17: Eye sensitivity curve

f

or

f

licker as per Kelly

1960 and Hen

g

er 1985

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 55 56

Comments to this Manuals

No comments