Power Density Targets for Efficient Lighting of Interior ... · Power Density Targets for Efficient...

april 2007 Laboratorium voor Lichttechnologie

Power Density Targets for Efficient Lighting of Interior

Task Areas

P Hanselaer, C Lootens, W Ryckaert, G Deconinck, P Rombauts

To be published LR&T 2007


2 [ / .100 /100 ]sysfinTA

PNPD W m lux W lm= =

Φ

.fin finTA TA TAA EΦ =

Normalized Power Density NPD

2

finTA

: Task Area (m )

E : maintained mean illuminance ( )TAA

lux

finTA : maintained luminous flux on TA ( )lumenΦ

: installed power for lightingsysP


NPD

• A measure of the efficiency to illuminate a specific task area

• It is not a measure of energy consumption, which depends on illumination levels, switch-on time, dimming, . . .


Actual criteriumNPD< 2.0 à 2.5 (W/m2.100 lux)

1. Based on best practice

Theoretical basis?

Non-standard task areas

EN 12464

shops, classrooms, musea?

2. Standard task area: floor (edge zone in-or excluded)


Purpose:determine a target NPD value

• lighting task as a starting point

• allowing arbitrary task areas;

• valid for a wide range of applications like offices, shops,

work areas, classrooms;

• simple and easy-to-use while being accurate and

reproducible;

• independent of a specific light calculation software and

related input and output parameters;

• visual comfort requirements are included


• efficiency to power the light source

• efficiency of converting electrical power to light

• efficiency of the luminaire

• efficiency of directing the luminous flux to the task area

• efficiency of maintaining the initial luminous flux.

sysfinTA

PNPD =

ΦsysP



efficiency to power the light source

sysfinTA

PNPD =

ΦsysP


lampgear

sys

PP

η =


efficiency of converting electrical power to light

sysfinTA

PNPD =

ΦsysP


inilamp

lamplampP

ηΦ

=


efficiency of the luminaire (Light Output Ratio)

sysfinTA

PNPD =

ΦsysP


inilum

inilamp

LOR Φ=Φ


efficiency of directing the luminous flux to the task area:

utilance (LDF, spacing, room reflectance)

sysfinTA

PNPD =

ΦsysP


iniTAinilum

U Φ=Φ


efficiency of maintaining

the initial luminous flux:

maintenance factor

sysfinTA

PNPD =

ΦsysP


finTAiniTA

MF Φ=Φ


Combining efficiencies

100. . . .

sysfinTA lamp gear

PNPD

MF U LORη η= =Φ

Minimal values:Selecting the best?

Eliminating the worst?

Maximum value


0.85gearη >

70 /lamp lm Wη >

0.75LOR >

0.75MF >

U > ???

Proposal:


Target value for utilance

Different methods (ray-tracing, point-by-point, flux transfer) with room reflectance and room index K as parameter and . . . standard task area

horizontal area .vertical area .( )

l wKh l w

= =+


Luminous flux on total room area:2 ...

2. 0.5

.

1

iniinilum

iniinilumlum

linilum um

with

ρ

ρ

ρ

ρ

Φ + + +

Φ= Φ <

<

>=− < >

< > Φ> Φ


Check: room: 6x6x3

=11 442 inilum lmΦ 0.5 / 0.5 / 0.5ρ = 0.7 / 0.5 / 0.3ρ =

A(m2) ( )E lux ( )ini lmΦ ( )E lux ( )ini lmΦ

Ceiling 36 103 3 708 76 2 736

Walls 72 146 10 530 128 9 216

Floor 36 237 8 532 231 8 316

Total 22 770 20 268

TA

0.5 could be too optimistic for downlighters0.5

ρρ< >=

=


2. . .inilum TA TA nTA nTAA E A EΦ = +

The luminous flux on total room areacan also written as

high: U will be low, low efficiency

low: U will be high, low lighting comfort nTA

nTA

E

E

2

1 .nTA nTA

TA TA

UE AE A

=+


0.5nTA TAE E<CIBSE, Luminance criteria

2

1 0.5 nTA

TA

U AA

>+

LE

ρπ

=

0.7

0.50.2

ceiling TA

wall TA

floor TA

L L

L LL L

=

=

=


0.85gearη >

70 /lamp lm Wη >

0.75LOR >

0.75MF >

Proposal:

2

1 0.5 nTA

TA

U AA

>+


Target value

2( / .100 ) (1.5 0.75 )nTA

TA

W m luxANPDA

< +

Task area!


(Non-)Task areaEdge zone included in task area (EN12464)


Preliminary tests


Test 1: standard task area

21nTA

TA

AA K

= +

1.5(2.25 )NPDK

< +


2

2.5

3

3.5

4

4.5

5

5.5

0 1 2 3 4 5 6

K

NPD

(W/1

00 lm

)

The formula offers theoretical basis for actual targets with standard task area!



– K=5 – U > 1.18– NPD < 2.55W/m².100lux

Large landscape office (30x30x3)



Indoor sport (44x23x8m)

– K= 1.888– U> 0.99– NPD< 3 W/m².100lux


Room: 6x6x3

Desk: 2x2

ATA=3x3=9

AnTA= 135

U>0.24

NPD < 12.8 W/m².100lux or maximum 115W/100 lux

Test 2: non-standard task area


Test 2: software calculations

385

40 !!!!

iniTAininTA

E lux

E lux

=

=

2

Three T5 lamps, 24 W, above deskPsys = 88 WU= 0.71 >>> 0.24

88NPD= 3.4 12.8 (target)9 .(2.9)

Wm

= <<


Test 2


Test 3: software calculations

46 !!!!

131 !!!!

iniTAininTA

E lux

E lux

=

=

2

Three T5 lamps, 24 W, cornerPsys = 88 WU= 0.085 <<< 0.24

88NPD= 28 12.89 .(0.35)

Wm

= >>


Test 3


Conclusions2( / .100 ) (1.5 0.75 )nTA

TA

W m luxANPDA

< +

• Easy, independent of software calculations

• In accordance with actual criterium for standard task areas

• Non – standard task areas: needs further testing

• Fine tuning for target values is possible

Thank you!

Power Density Targets for Efficient Lighting of Interior ... · Power Density Targets for Efficient...

Documents

Transcript of Power Density Targets for Efficient Lighting of Interior ... · Power Density Targets for Efficient...