E direct WP = F x UF (0,0,0) x MF Area of working plane E direct W = F x (DLOR UF (0,0,0) ) x MF Area of 4 walls E direct C = F x ULOR x MF Area of ceiling cavity K. F. Chan (Mr.) MEBS 6002 1 SCALAR ILLUMINANCE E s is the average illuminance on the surface of an infinitesimally small sphere at a point in space. K. F. Chan (Mr.) MEBS 6002 2 1
SCALAR ILLUMINANCE For point sources, direct illumination E s = E max 4 For satisfactory appearance, the mean scalar illuminance should be at least 40% of the illuminance on the horizontal plane. K. F. Chan (Mr.) MEBS 6002 3 For inter-reflected illumination E s = E h (k+0.5ρ) K. F. Chan (Mr.) MEBS 6002 4 2
VECTOR/SCALAR RATIO K. F. Chan (Mr.) MEBS 6002 5 Single point source K. F. Chan (Mr.) MEBS 6002 6 3
Multiple point source K. F. Chan (Mr.) MEBS 6002 7 Single diffuse K. F. Chan (Mr.) MEBS 6002 8 4
MODELLING EFFECT K. F. Chan (Mr.) MEBS 6002 9 CYLINDRICAL ILLUMINACE For point source,direct illumination Ec = Emaxsinθ π For inter-reflected light, Ec = 1.5Es 0.25 Eh(1+ρ f ) where ρ f = reflectance of the floor cavity Cylindrical illuminance gives better guide to the lighting of vertical surfaces. K. F. Chan (Mr.) MEBS 6002 10 5
CYLINDRICAL ILLUMINANCE Ec/Eh 0.1 0.6 0.9 Modelling Harsh Good Weak For a satisfactory installation, mean cylindrical illuminance should be at least 0.4 of the horizontal illuminance. K. F. Chan (Mr.) MEBS 6002 11 VECTOR ILLUMINATION The illumination vector at a point is the maximum difference of the illuminance across diameters of an infinitesimally small sphere at that point. Vector/Scalar ratio 0.5 1.5 4 Modelling Weak Good Harsh Appearance Dull Pleasant Unacceptable K. F. Chan (Mr.) MEBS 6002 12 6
K. F. Chan (Mr.) MEBS 6002 13 K. F. Chan (Mr.) MEBS 6002 14 7
K. F. Chan (Mr.) MEBS 6002 15 K. F. Chan (Mr.) MEBS 6002 16 8
MODELLING EFFECT Direct ratio Flux fraction ratio Vector/scalar illuminance ratio, 1.2 to 1.8. K. F. Chan (Mr.) MEBS 6002 17 ROOM APPEARANCE Direct ratio Flux fraction ratio Wall / ceiling illuminance ratio K. F. Chan (Mr.) MEBS 6002 18 9
ROOM APPEARANCE DR = DF F DLOR FFR =ULOR DLOR K. F. Chan (Mr.) MEBS 6002 19 ROOM APPEARANCE K. F. Chan (Mr.) MEBS 6002 20 10
Illuminance Ratio K. F. Chan (Mr.) MEBS 6002 21 Illuminance Ratio K. F. Chan (Mr.) MEBS 6002 22 11
MULTIPLE CRITERION DESIGN Recommended Ewall/Eh between 0.5 and 0.8 Recommended Eceiling/Eh between 0.3 and 0.9 Preferred E/Es between 1.2 and 1.8 (* see IES TR15 July, 1997 and page 75 to 78 of CIBSE Code for Lighting 2002) K. F. Chan (Mr.) MEBS 6002 23 VECTOR / SCALAR RATIO K. F. Chan (Mr.) MEBS 6002 24 12
RECOMMENDED REFLECTANCES TO ACHIEVE LUMINANCE RATIO K. F. Chan (Mr.) MEBS 6002 25 ROOM APPEARANCE Any brightly lit surface will appear to recede from the observer high overall illuminance makes an interior look more spacious. A room with bright ceiling and dark walls will seem taller and more formal. A room with brighter walls will seem friendlier and larger in plan. A room with dark ceiling will give an oppressive feeling. K. F. Chan (Mr.) MEBS 6002 26 13
Class of visual task Critical, often with a fixed direction of view Critical, but general direction of view Ordinary task with general direction of view Large task or limited viewing time No specific visual task or direction of view GLARE Examples Drawing offices, very fine inspection Offices, libraries, computer buildings Kitchens, reception areas, fine assembly work Stockrooms, medium assembly work Rough industrial work, indoor parking areas. Limiting glare index 16 19 22 25 28 K. F. Chan (Mr.) MEBS 6002 27 INSTALLED POWER DENSITY (Taken from Table 2.5 of CIBSE Code for Lighting, 2002) K. F. Chan (Mr.) MEBS 6002 28 14
DISPLAY ILLUMINANCE RATIO Display Effect Subtle Moderate Strong Dramatic Illuminance Ratio 5:1 15:1 30:1 50:1 Apparent Brightness Ratio 2.5:1 5:1 7:1 10:1 K. F. Chan (Mr.) MEBS 6002 29 K. F. Chan (Mr.) MEBS 6002 30 15