Age: a human factor in lighting

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Age: a human factor in lighting

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AGE, A HUMAN FACTOR IN LIGHTING

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Proceedings of the 1984 International Conference

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Vol. 1, Research Reports and Case Studies

p. 508-512

Reprinted with permission from

Human Factors Association of Canada

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DBR Paper No. 1241

Division of Building Research

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PROCEEDINGS OF THE 1984 INTERNATIONAL CONFERENCE ON C)CCUPAflONAL ERGONOMICS

AGE, A HUMAN FACTOR I N LIGHTING G.A. Wright and M.S. Rea D i v i s i o n of B u i l d i n g Research N a t i o n a l R e s e a r c h C o u n c i l Canada

Ottawa, O n t a r i o , Canada ABSTRACT

V i s u a l performance i n t h e workplace i s determined by t h e s t i m u l u s c o n d i t i o n s a s w e l l a s t h e a g e o f t h e employee. From a n a n a l y s i s o f v i s u a l performance d a t a a t a s i m l a t e d r e a l i s t i c t a s k and a n e x a m i n a t i o n of t h e l i t e r a t u r e on a g i n g , it a p p e a r s t h a t o l d e r s u b j e c t s a r e 1) s l w e r and more c a u t i o u s i n r e s p o n d i n g and 2) s u f f e r from r e d u c e d r e t i n a l i l l u m i n a t i o n and c o n t r a s t . I n p r a c t i c e , t h e r e l a t i v e v i s u a l performance of o l d e r s u b j e c t s w i l l b e more s e n s i t i v e t h a n t h a t of younger s u b j e c t s t o r e d u c t i o n s i n s t i a u l u s c o n t r a s t and i l l u m i n a t i o n l e v e l s . INTRODUCTION A s i g n i f i c a n t component i n t h e d e s i g n of t h e o c c u p a t l o n a l environment i s t h e s e l e c t i o n and arrangement of t h e v i s u a l s c e n e f o r q u i c k and a c c u r a t e performance of v i s u a l t a s k s . T h a t i s , i t i s i m p o r t a n t t o d e s i g n t h e luminous environment of t h e workplace f o r optirmm v i s u a l performance. The s u c e s s f u l d e s i g n w i l l be based n o t o n l y on t h e v l s u a l c h a r a c t e r i s t i c s of t h e t a s k , b u t a l s o o n t h e way t h a t l i g h t is d e l i v e r e d t o t h a t t a s k and on t h e p e r s o n s e e i n g i t . T h i s t a l k emphasizes t h e l a s t c o n s i d e r a t i o n , t h e i n d i v i d u a l a s c h a r a c t e r i z e d by c h r o n o l o g i c a l age. It i s a r g u e d t h a t t h e t a s k , t h e l i g h t i n g and t h e i n d i v i d u a l must be c o n s i d e r e d s i m u l t a n e o u s l y f o r p r o p e r d e s i g n of t h e v i s u a l environment. There i s a g r e a t d e a l of l i t e r a t u r e employing many methodologies d e a l i n g w i t h t h e a g i n g i n d i v i d u a l (Blackwell and B l a c k w e l l , 1980;

Blackwell, 1982; Boyce, 1973; C a r t e r , 1982; Corso,

1971; F i s h e r and C h r i s t i e , 1965; Fozard e t

a1,

1977; Guth and McNellis, 1969; MacFarland et a l ,

1960; McGrath and Morrison, 1981; Muck and Bodmann,

1961; Ordy and B r i z z e e , 1979; Owsley e t a l , 1983;

R l c h a r d s , 1977; S a i d and Weale, 1959; Smith and Rea, 1978; Welsh e t a l , 1977; Wolf, 1960). These s t u d i e s may be roughly c l a s s i f i e d i n t o 1) b a s i c s t u d i e s w i t h l i t t l e i n t e r e s t i n a p p l i e d problems o r 2) a p p l i e d s t u d i e s w i t h l i t t l e a t t e n t i o n t o fundamental i s s u e s . The b a s i c s t u d i e s d e l i b e r a t e l y a t t e m p t t o remove t h e c o m p l e x i t i e s from t h e problem, t h a t i s , t h o s e c o m p l e x i t i e s t h a t make t h e t a s k ' l i f e l i k e ' . The a p p l i e d s t u d i e s may s e r i o u s l y confound f a c t o r s s o t h a t i t i s d i f f i c u l t o r i m p o s s i b l e t o s e p a r a t e t h e v i s u a l from t h e n o n v i s u a l d e t e r m i n a n t s of behavior. I n t h i s r e p o r t we t r y t o expl.ain t h e b e h a v i o r of o l d e r and younger i n d i v i d u a l s a t a s i m l a t e d realistic t a s k w i t h i n f o r m a t i o n g l e a n e d from t h e l i t e r a t u r e r e l a t e d t o aging. A s i n most of t h e s e s t u d i e s t r y i n g t o b r i d g e b a s i c s c i e n c e and a p p l i c a t i o n , we must t r y t o p i e c e t o g e t h e r a g e n e r a l p i c t u r e of how t h e human system i s working. T h e r e f o r e , we r e l y h e a v i l y upon parsimony r a t h e r t h a n p r o o f . That i s , we t r y t o p r e s e n t t h e s i m p l e s t p o s s i b l e e x p l a n a t i o n of t h e o b s e r v e d r e s u l t s r a t h e r t h a n e x p e r i m e n t a l l y e x h a u s t a l l p o s s l b l e a l t e r n a t i v e hypotheses. I n t h i s way we begin a t h e o r y of t h e performance of t h e a g i n g v i s u a l system, and we e x p e c t t o r e f i n e t h a t t h e o r y a s more e x h a u s t i v e r e s e a r c h i s completed.

THE SIMULATED REALISTIC VISUAL TASK Smith and Rea (1980) c o n d u c t e d a s i r m l a t e d r e a l i s t i c v i s u a l t a s k u s i n g young s u b j e c t s ( a g e s 2 0

t o 24) and o l d e r s u b j e c t s ( a g e s 6 0 t o 69). A l l younger s u b j e c t s had e x c e l l e n t u n c o r r e c t e d v i s i o n . The o l d e r s u b j e c t s had b e e n r e c e n t l y examined by a n o p t o m e t r i s t , and p r o v i d e d w i t h t h e p r o p e r o p t i c a l c o r r e c t i o n s f o r reading.

A l l s u b j e c t s compared two columns o f t y p e d number lists " a s q u i c k l y and a c c u r a t e l y a s p o s s i b l e . " Each l i s t c o n t a i n e d 20, f i v e - d i g i t numbers. Zero t o s i x o n e d i g i t d i s c r e p a n c i e s were

randomly i n t e r s p e r s e d i n o n e of t h e lists. One l i s t was p r i n t e d b o t h i n g r e y i n k ( l o w c o n t r a s t ,

0.3) and i n b l a c k i n k ( h i g h c o n t r a s t , 0.8) ( s e e Eq. 1). The o t h e r l i s t was p r i n t e d i n h i g h

c o n t r a s t . The l i s t s were viewed i n a w h i t e c u b i c l e under e i g h t d i f f e r e n t i l l u m i n a n c e s , g i v i n g e i g h t

d i f f e r e n t t a s k luminances.

Time t o complete t h e l i s t s and e r r o r s ( m i s s e s and f a l s e p o s i t i v e s ) were combined i n t o a

perfomance s c o r e . These d a t a a r e p l o t t e d i n F i g u r e 1.

The Absolute D i f f e r e n c e i n Performance

Immediately o b v i o u s from F i g u r e 1, i s t h e a b s o l u t e d i f f e r e n c e i n t h e performance of t h e two groups of s u b j e c t s . A g r e a t d e a l of l i t e r a t u r e i n d i c a t e s t h a t n o n v i s u a l f a c t o r s i n f l u e n c e t h e performance of o l d e r workers. The s p e e d o f p r o c e s s i n g v i s u a l i n f o r m a t i o n s l o w s down w i t h a g e

(Walsh, 1982). S e v e r a l i n v e s t i g a t o r s h a v e s u g g e s t e d t h a t e l d e r l y s u b j e c t s a r e a l s o more c a u t i o u s and c o n s e r v a t i v e t h a n younger o n e s (Calhoun and Hutchinson, 1981; Hutman and S e k u l e r ,

1980). F u r t h e r . p o o r e r performance may b e a r e s u l t of reduced motor s k i l l s (Weston, 1951). It i s n o t u n r e a s o n a b l e t o e x p e c t t h a t t h e s e n o n v i s u a l f a c t o r s might m a n i f e s t themselves a s a b s o l u t e d i f f e r e n c e s i n performance e v e n u n d e r i d e a l v i s u a l c o n d i t i o n s . T h e r e f o r e we n o r m a l l z e d t h e o l d e r s u b j e c t d a t a t o t h e younger s u b j e c t d a t a by a f i x e d a u l t i p l l e r of 1.222 u n d e r t h e a s s m p t i o n t h a t n o n v i s u a l f a c t o r s produced t h e a b s o l u t e s h i f t i n performance,

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PROCEEDINGS OF THE 1984 INTERNATIONAL CONFERENCE ON OCCUPATIONAL ERGOWOMICS

4-.-;:&,~:--~

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Y O U N G 1 2 0 - 2 4 )

BLACK INK. ACTUAL DATA GRAY INK, ACTUAL OATA

0 B M C K INK. OLDER OATA TRANSFORMED

0 GRAY INK. OLDER DATA TRANSFORMED

F i g u r e 1

A G E , y e a r s The v i s u a l performance s c o r e s of o l d e r and younger

s u b j e c t s a t t h e n u m e r i c a l verification t a s k ( f r o m F i g u r e 2

Smith and Rea, 1980

-

c l o s e d symbols) w i t h

t r a n s f o r m e d s c o r e s from o l d e r s u b j e c t s ( o p e n An estLmate of r e l a t i v e d e c l i n e I n r e t i n a l symbols). Score is a combination of time t o i l l u m i n a n c e w i t h a g e ( a f t e r Weale, 1961). complete t h e number l i s t comparison and e r r o r s

(omlsslon and commlsslon) made d u r i n g comparison.

R e t i n a l c o n t r a s t . B e s i d e s t h e r e d u c t i o n i n t h e amount of l l g h t r e a c h i n g t h e r e t i n a . t h e and t h a t t h e s e n o n v i s u a l f a c t o r s d i d n o t i n t e r a c t w i t h t h e v i s u a l f a c t o r s i n d e t e r m i n i n g t h e v i s u a l performances of e i t h e r group of s u b j e c t s a t t h i s t a s k . The D i f f e r e n c e i n R e l a t i v e Performance I n a very g e n e r a l way, v i s l o n can be c o n s l d e r e d a s a s e r i a l p r o c e s s . L i g h t i s t r a n s m i t t e d from t h e environment through t h e o p t i c a l media t o t h e l i g h t sensitive r e t l n a . The r e t i n a c o n v e r t s l i g h t t o n e u r a l s i g n a l s t h a t a r e t r a n s m i t t e d from t h e r e t i n a , o v e r t h e o p t i c n e r v e , t o t h e b r a i n . Because of t h l s s e r i a l n a t u r e , i t i s n e c e s s a r y t o account f o r t h e o p t i c a l changes i n t h e e y e b e f o r e one c o n s i d e r s t h e more complex ( a n d p a r a l l e l ) n e u r a l p r o c e s s i n g of t h e v i s u a l system. R e t i n a l i l l u m i n a n c e . A s one a g e s , l e s s l i g h t i s t r a n s m i t t e d t h r o u g h t h e o ~ t i c a l media. On a v e r a g e , r e t i n a l i1l;mination a t t h e age of 60 i s a b o u t o n e t h i r d o f t h a t a t 20 (Weale, 1961). While t h e r e a r e numerous r e a s o n s f o r t h i s d e c r e a s e , t h e predominant f a c t o r s a r e s e n i l e m i o s i s ( d e c r e a s e i n p u p i l s i z e ) and an i n c r e a s i n g o p a c i t y , o r y e l l w i n g , of t h e l e n s . A c t u a l l y , t h e s e two f a c t o r s combine t o r e d u c e r e t i n a l i l l u m i n a t i o n more t h a n might b e expected. S m a l l e r p u p i l s i z e s f o r c e most of t h e l i g h t t o p a s s through t h e t h i c k e r n u c l e a r r e g i o n of t h e l e n s , which a b s o r b s more l i g h t t h a n t h e margins of t h e l e n s . With t h i s i n mind, Weal made h i s e s t i m a t e s of t h e expected r e d u c t i o n i n r e t i n a l i l l u m i n a n c e f o r w h i t e l i g h t w i t h a g e ( F i g u r e 2). q u a l i t y of l i g h t - r e a c h i n g t h e r e t i n a i s - a i s o reduced. R e t l n a l c o n t r a s t may b e r e d u c e d by b l u r r i n g of t h e image o r by s c a t t e r i n g . The i n c r e a s e d image b l u r r i n g w i t h a g e c a n b e a t t r i b u t e d t o changes i n c o r n e a l a s t i g m a t i s m and l e n t i c u l a r s p h e r i c a l r e f r a c t i o n ( S l a t a p e r , - 1 9 5 0 ; Weise, 1959; Weale, 1963). F u r t h e r , p r e s b y o p i a , t h e d e t e r i o r a t i o n i n t h e a b i l i t y t o f o c u e t h e e y e , 1s c o r r e l a t e d w i t h a g e (Bruckner, 1967). Although t h e s e f a c t o r s c a n be major determinants of c o n t r a s t r e d u c t i o n o n t h e r e t i n a , t h e y c a n b e l a r g e l y c o r r e c t e d t h r o u g h o p t o m e t r i c l e n s e s . L i g h t s c a t t e r i n g i s a l s o a s i g n i f i c a n t f a c t o r I n t h e d e g r e d a t i o n of r e t i n a l c o n t r a s t , b u t l t c a n n o t b e d i r e c t l y a l l e v i a t e d by o p t i c a l c o r r e c t i o n s . I n g e n e r a l , s c a t t e r i s expected t o i n c r e a s e w i t h a g e d u e t o t h e i n c r e a s i n g t u r b i d i t y of t h e l e n s (Corso, 1981, p. 40). I n s e v e r e c a s e s c a t a r a c t s form and must b e s u r g i c a l l y r e p l a c e d w i t h p r o s t h e t i c l e n s e s . A l l e n and Vos (1967) a s w e l l a s Wolf and Gard.lner (1965) h a v e q u a n t i t a t i v e l y demonstrated t h e i n c r e a s e i n s t r a y l i g h t w i t h a g e due t o s c a t t e r i n t h e l e n s . A l l e n a n d Vos e s t i m a t e d a " f o u r f o l d i n c r e a s e i n s c a t t e r i n t h e a n t e r i o r e y e media from a g e 1 0 t o 80 ( w i t h c o n s i d e r a b l e i n d i v i d u a l d i f f e r e n c e s ) . " They e s t i m a t e d t h e amount o f s c a t t e r i n young a d u l t e y e s ( a g e 20 t o 3 0 ) t o b e a b o u t 1.5%. and a b o u t 3% f o r o l d e r e y e s ( a g e s 6 0 t o 70) ( F i g u r e 3). E a r l i e r , u s i n g more d i r e c t measurements of s c a t t e r from t h e

l e n s , Wolf and G a r d i n e r p r o v i d e d d a t a t h a t s h a r e d a much more d r a m a t i c i n c r e a s e i n s c a t t e r by t h e s e v e n t h decade. They e s t l m a t e d a n e l e v e n f o l d

(6)

PROCEEDINGS OF THE 1984 INTERNATIONAL CONFERENCE ON OCCUPATIONAL ERGONOMICS

a l s o t o t h e d i f f e r e n t t e c h n i q u e s employed t o e s t i m a t e s c a t t e r .

ANALYSIS OF THE SMITH-REA DATA

A G E , y e a r s

F i g u r e 3

An e s t i m a t e of i n c r e a s e i n s c a t t e r by t h e a n t e r i o r eye due t o a g i n g ( a f t e r A l l e n and Vos, 1967).

Reduction i n r e t i n a l i l l u m i n a n c e and c o n t r a s t s h o u l d a f f e c t v i s u a l performance. _{We wanted t o s e e} i f , by a c c o u n t i n g only f o r t h e o p t i c a l changes produced by a g i n g , we c o u l d e x p l a i n t h e performance of t h e o l d e r s u b j e c t s a t t h e numerical v e r i f i c a t i o n t a s k u s e d by Smith and Rea.

The p h y s i c a l c o n t r a s t (C+) of a t a s k may b e c a l c u l a t e d by t h e f o r m l a : where: Lt is t h e luminance ( b r i g h t n e s s ) of t h e t a r g e t ( a p r i n t e d d i g i t ) Lb 1s t h e luminance ( b r i g h t n e s s ) of t h e t a r g e t background ( t h e p a p e r on which t h e d i g i t i s p r i n t e d ) . S c a t t e r can be c o n s i d e r e d as a redistribution o f luminance. Because of t h e l a r g e s p a t i a l e x t e n t of t h e background i n t h e Smith-Rea e x p e r i m e n t , t h e r e d i s t r i b u t i o n of luminance p r o d u c e s no n e t change i n t h e v a l u e of Lb i n Eq. 1. However, a p r o p o r t i o n ( s ) of l i g h t s c a t t e r e d from t h e background w i l l be added t o t h e t a r g e t . S i m i l a r l y , s c a t t e r w i l l r e d u c e t h e luminance of t h e t a r g e t by a f a c t o r of (1-s). I n o t h e r words, t h e s c a t t e r e d luminance from t h e background i s added t o t h e remaining, u n s c a t t e r e d t a r g e t luminance. S c a t t e r from t h e l e n s w i l l . t h e r e f o r e . r e d u c e t h e

d i f f e r e n c e i n luminance a t th; b o r d e r between t h e t a r g e t and i t s background. The e f f e c t of s c a t t e r on r e t i n a l c o n t r a s t (C ) raight t h e r e f o r e be modelled by t h e f ollow4ng e q u a t i o n :

c y

I (Lb

-

( ( l - s ) L t + 6 L ~ ) )

/

Lb ( 2 ) Y u R e a r r a n g i n g terms: Z Q Z

c y

I ( ( L b ' L t )

/

L b )

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L ~ ) ( 3 ) L

I,

or:

c,

-

C + ( l - s ) ( 4 To e s t i m a t e t h e r e l a t i v e d e c r e a s e i n r e t i n a l A G E , y e a r s _{c o n t r a s t due t o age}_{( AC}

_'1,

_{we s u b t r a c t from t h e}

r e t i n a l c o n t r a s t of t h e younger e y e (CY--), t h e r e t i n a l c o n t r a s t of t h e o l d e r eye (C )! F i g u r e 4 40 An e s t i m a t e of t h e i n c r e a s e i n s c a t t e r e d l i g h t ( l o g m i l i l a m b e r t s ) by t h e l e n s due t o a g i n g ( a f t e r Wolf and G a r d i n e r , 1965). (1mL = 3.183 cd me2) l n c r e a s e i n s c a t t e r from t h e l e n s between t h e t h i r d and s e v e n t h d e c a d e ( F i g u r e 4 ) . Based upon t h e e s t i m a t e d s c a t t e r f o r young e y e s from A l l e n and Vos

(1.5%). one would e x p e c t s c a t t e r t o b e i n t h e nelghborhood of 16% by age 65, a c c o r d i n g t o t h e s e d a t a from Wolf and G a r d i n e r . Thus, t h e r e seems t o be a wide v a r i a t i o n i n t h e e s t i m a t e of t h e i n c r e a s e i n s c a t t e r w i t h age. T h i s v a r i a t i o n i s probably due not o n l y t o i n d i v i d u a l d i f f e r e n c e s i n t h e e y e s of matched a g e s (which i s w e l l documented), b u t

where: sy i s t h e p r o p o r t i o n of s c a t t e r i n t h e younger e y e ,

s o i s t h e p r o p o r t i o n of s c a t t e r i n t h e o l d e r eye.

Thus.

From A l l e n and Vos (1967) and Wolf and G a r d i n e r ( 1 9 6 5 ) , t h e so v a l u e s i n Eq. ( 7 ) could be between 0.03 and 0.16, and s would be e q u a l t o 0.015, f o l l o w i n g A l l e n and 40s. T h e r e f o r e , one would

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PROCEEDINGS OF THE 1984 INTERNATIONAL CONFERENCE ON OCCUPATIONAL ERGONOMICS

e x p e c t AC6 t o be reduced by a f a c t o r between r e d u c t i o n i n r e t i n a l c o n t r a s t , a l t h o u g h t h e y d o t r y

0.015 and 0.145 (1.5% and 14.5%). t o a c c o u n t f o r t h e r e d u c t i o n i n r e t i n a l

i l l u m i n a n c e . So i t seems, a t l e a s t , more

Rea (1982, 1983) h a s r e c e n t l y developed a parsimonious, i f n o t more a p p r o p r i a t e g i v e n t h e

model of s u p r a t h r e s h o l d v i s u a l performance f o r t h e s e r i a l n a t u r e o f v i s u a l p r o c e s s i n g . t o d i m i n i s h t h e

k i n d of t a s k used by Smith and Rea. The model

is

importance of n e u r o l o g i c a l changes i n t h e v i s u a l

g r a p h i c a l l y p r e s e n t e d i n F i g u r e 5. T h i s model i s system, a t l e a s t b e f o r e t h e s e v e n t h d e c a d e , u n t i l

based upon t h e performance of younger s u b j e c t s , b u t more d e f i n i t i v e d a t a a r e a v a i l a b l e .

assuming t h a t o p t i c a l c h a n g e s c a n a c c o u n t f o r t h e

changes i n t h e r e l a t i v e performance of o l d e r IMPLICATIONS FOR PRACTICE

s u b j e c t s , i t s h o u l d be p o s s i b l e t o t r a n s f o r m t h e

d a t a from o l d e r s u b j e c t s t o match t h e d a t a from We b e l i e v e t h a t t h i s a n a l y s i s o f f e r s i n s i g h t

younger s u b j e c t s by a d j u s t i n g o n l y t h e luminance i n t o t h e d e s i g n of luminous e n v i r o n m e n t s f o r o l d e r

and c o n t r a s t v a l u e s f o r t h e o l d e r s u b j e c t s . I n i n d i v i d u a l s . F i r s t , we s e e t h a t t h e b r i g h t n e s s of

o t h e r words, i t s h o u l d be p o s s i b l e t o model t h e t a s k s a f f e c t s t h e r e l a t i v e performance of o l d e r

r e d u c t i o n i n r e t l n a l i l l u m i n a n c e and i n t h e r e t i n a l s u b j e c t s more t h a n i t d o e s younger s u b j e c t s a t a

image q u a l i t y by t r a n s f o r m a t i o n s a l o n g t h e s e two s i m u l a t e d r e a l i s t i c t a s k . From t h e l i t e r a t u r e and

d i m e n s i o n s , i f t h e v i s u a l a g e e f f e c t s a r e o n l y t h l s a n a l y s i s , t h i s r e d u c t i o n i s due, i n p a r t , t o

o p t i c a l . l e s s l i g h t r e a c h i n g t h e r e t i n a of t h e o l d e r eye.

I n p r a c t i c e t h i s w i l l many t i m e s t r a n s l a t e i n t o

S p e c i f i c a l l y , i t was p o s s i b l e t o make t h e d a t a h i g h e r r e q u i r e d i l l u m i n a t i o n l e v e l s f o r o l d e r

from t h e o l d e r s u b j e c t s c l o s e l y match t h e d a t a from workers. Second, l o w e r c o n t r a s t w i l l a f f e c t t h e

t h e younger s u b j e c t s , o v e r t h e range of t h e model, performance of o l d e r s u b j e c t s more t h a n younger

by r e d u c i n g t h e r e t i n a l i l l u m i n a n c e by s u b j e c t s a t t h i s t a s k . Again, from t h e l i t e r a t u r e

0.5 l o g cd/m2 and t h e r e t i n a l c o n t r a s t by 109. and t h i s a n a l y s i s , t h e r e d u c t i o n is due t o a

( F i g u r e 1 ) . These r e l a t i v e rectuctions i n r e t i n a l r e d u c t i o n i n t h e imaging q u a l i t y i n t h e o l d e r eye.

i l l u m i n a n c e and c o n t r a s t f o r o l d e r s u b j e c t s of t h i s High c o n t r a s t p h o t o d u p l i c a t i o n s o r h i g h e r c o n t r a s t

a g e group were chosen t o b e i n a c c o r d a n c e w i t h l e t t e r s and numbers o n v i s u a l d i s p l a y u n i t s may b e

t h o s e s t u d i e s c i t e d e a r l i e r . With t h e s e e s t i m a t e s needed f o r o l d e r r e a d e r s . These f a c t o r s of

of a g e - r e l a t e d o p t i c a l changes and w i t h t h e b r i g h t n e s s a n d c o n t r a s t i n t e r a c t t o lower t h e

s u p r a t h r e s h o l d v i s u a l performance model f o r younger v i s u a l perfomance of o l d e r workers. A t low

s u b j e c t s , i t seems u n n e c e s s a r y t o i n v o k e a n b r i g h t n e s s e s and low c o n t r a s t s t h e v i s i o n of o l d e r

e x p l a n a t i o n of age e f f e c t s based upon n e u r o l o g i c a l workers c a n b e v e r y s e r i o u s l y a f f e c t e d , b u t a t h i g h

changes i n t h e v i s u a l system. c o n t r a s t s r e l a t i v e performance w i l l r e m a i n f a i r l y

h i g h o v e r a wide range of b r i g h t n e s s e s (Smith and

T h i s c o n c l u s i o n s t a n d s i n o p p o s i t i o n , f o r Rea, 1980).

example, t o t h a t from Owsley e t a 1 (1983). It must

be remembered t h a t t h e d a t a used t o j u s t i f y e i t h e r F o r many i n d u s t r i a l and commercial t a s k s where

i n t e r p r e t a t i o n a r e h i g h l y v a r i a b l e . N e v e r t h e l e s s , o l d e r p e o p l e a r e employed, t h e a n a l y s i s of t h e

Owsley e t a 1 make no a t t e m p t t o a c c o u n t f o r t h e l i g h t i n g and t h e t a s k w i l l b e more c r i t i c a l t h a n i t

w i l l b e f o r younger people. With f u r t h e r

development of t h e s u p r a t h r e s h o l d v i s u a l

performance model and a more e x t e n s i v e d a t a b a s e o n

a g i n g , i t s h o u l d b e p o s s i b l e t o p r o v i d e b e t t e r

c a l c u l a t i o n p r o c e d u r e s of v i s i b i l i t y i n t h e working luminous environment.

Acknowledgement

The a u t h o r s w i s h t o thank P i e r r e Landry and

Mike O u e l l e t t e f o r t e c h n i c a l a s s i s t a n c e . T h i s paper is a c o n t r i b u t i o n from t h e D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i p n a l R e s e a r c h C o u n c i l Canada, and is p u b l i s h e d w i t h t h e a p p r o v a l of t h e D i r e c t o r of t h e D i v i s i o n . REFERENCES A l l e n , M.J. and Vos, J.J. O c u l a r s c a t t e r e d l i g h t

and v i s u a l performance a s a f u n c t i o n of age. American J o u r n a l of Optometry and A r c h i v e s of b e r i c a n k a d e m y o f Optometry, 1967, November, 717-727.

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G r a p h i c a l r e p r e s e n t a t i o n of s u p r a t h r e s h o l d v i s u a l of 235 o b s e r v e r s of v a r y i n g a g e s . J o u r n a l of t h e

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