PLS 2014: From Specification to Lighting Reality

“From Specification to Lighting Reality” ILP Summit–September 2014

Emily Bolt – Bid Manager – Public Lighitng

Thorn Lighting

“From Specification to Lighting Reality” ILP Summit–September - 2014

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08/10/20142


“Apples with Apples”

A look at how LED lumen package data may be presented in different ways and examining

how an apples with apples comparison may be made. It addresses a number of key

aspects such as :

Is data presented for the LED chip only under flash test conditions?

Is the data presented at very low junction temperatures? Is that realistic?

What format of data is being presented? Is relative photometry being applied or is the

data based on absolute photometry?

08/10/20143


Junction Temperature Tj – Inside an LED chip is a junction between

two materials, one positively charged and one negatively charged. (pn

Junction) Light is emitted from this junction by the exchange of electrons

between the two materials and, as a side effect, heat is generated at the

junction. The junction temperature needs to be controlled to ensure that

the light output and LED lifetime fulfil the requirements of a given

application.

Ambient Temperature ta – When any testing is performed on a

product it is for a defined surround temperature. This is the ambient

temperature and defined as ta. The standard ta defined for testing is

25deg C although testing an another value is permissible as long as the

temperature is declared.

08/10/20144


So ….

Ta = 25° C or 15° C (for street lighting)

Change in lumen output is approx 2% but extended life.

Tj = 60° C – 85° C (@Ta 25deg C)

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08/10/20146

What is the LOR?

LOR = luminaire output

lamp output

Luminaire Output = lamp output x LOR

e.g. lamp output of a 50W HST = 3400lms

3400 x 0.7 = 2380lms


08/10/20147

We generally cannot measure LOR

for an LED luminaire therefore it is

recommended that Absolute

Photometric values are used.

Absolute Photometry results in a

LOR = 1.0


Efficacy – How efficiently a light source converts electricity into light.

Lamp Efficacy

Lm/W = lamp lumens

circuit watts

Luminaire Efficacy

LLm/W = lamp lumens x LOR

circuit watt

For LED we should always use the Luminaire Efficacy i.e. LOR = 1.0

08/10/20148


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08/10/201410


Lumen packages

The table below shows 3 different luminaires the common denominator is that all three have

a circuit wattage of 28W:

08/10/201411

A B C

Lumen Package 3072 3200 2360

Lumen Package @ Ta = 15deg 2826 3200 2407

LOR 0.7 0.8 1.0

Lumen Output 1978 2560 2407

A B C

Lamp Efficacy lm/w 101 114 107

Luminaire Efficacy Llm/w 71 91 86


“Apples with Apples”

We look at Correlated Colour Temperature (CCT) and the debate regarding the correct

selection for an application including how this affects the lighting solutions taking into

consideration the impact on the energy efficiency of the overall scheme. We ask the

following:

Is the SP ratio and lumen package correct for the CCT specified?

Is the CRI specified for the correct application?

08/10/201412


Correlated Colour Temperature (CCT) – may be either coloured, typically

red/green/blue/amber or white. However, similar to daylight, white can vary from a warm

white with a higher red content to a cool white with a higher blue content.

08/10/201413


BS5489-1:2013

LED CCT vs. SP Ratio

08/10/201414

CCT Luminaire Lumen Output SP ratio

3000K 4967 1.2

4000K 5340 1.5

5700K 5773 1.9


CCT vs Energy Saving

Based on a standard 10m wide road @ 33m spacing

08/10/201415

CCT 3000K 4000K 5700K 3000K 4000K 5700K

Lumen Package 1950 2200 2440 8400 8600 9000

SP Ratio 1.2 1.5 2 1.2 1.5 2

Circuit Wattage 26 24 19 110 90 82

P4 P1

Lighting Classification

“The Truth About LED”Hen on the Road –March - 2014

08/10/201416

Colour Rendering Index (CRI) – every light source is characterised according to how

well it distinguishes colours. This is described by an Ra number where the higher the

number the more accurately the colours are displayed.

• IEC/PAS62717, Clause 9.3 (20 Samples tested)

• Measurements made initially and at the end of a 6000hr (or 25% of life – if shorter) time

period.

• Initial rated CRI values shall not vary by more than 3-points

• Maintained CRI values shall not vary by more than 5-points


08/10/201417

BENCHMARK TEST ON LED REPLACEMENTS OF DIRECTIONAL HALOGEN LAMPS

Bouroussis, C.A., Doulos, L.T., Madias E.-N.D., Topalis, F.V.

Lighting Laboratory, National Technical University of Athens, Athens, GREECE.

LUX EUROPA 2013. KRAKOW


08/10/201418

Colour Rendering Index (CRI)

What does BS5489-1:2013 state?


08/10/201419

Application Ra Value

Street Lighting > 20

High Pedestrian usage >60

Indoor Lighting 80

Sports Lighting 80+

High End Designer Store 90

“Maintenance Factors, The meaning of Life and Constant Light Output”

“The meaning of Life”

We also look at The Meaning of Life,

exploring lifetime claims made for LED,

how we measure lifetime in terms of lumen

depreciation and, importantly, parametric

failures (By). We examine how these

affect overall lifetime figures and

maintenance factor helping engineers to

make informed decisions on LED

specifications and how this will affect the

lighting solution on the ground

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08/10/201421

Rated Life

Lumen Maintenance (Lx)

X = percentage of light output

remaining at the end of rated lifetime

E.g. L70 (100,000hr) = 70% of initial

light output should still be expected

to be produced after 100,000 hrs of

LED operation.

IEC/PAS62717 (clause 10.2) checks

lumen maintenance over a 6000hr

test period.

IES TM-21recommends lumen

maintenance over 10,000hrs.

TM - 21


08/10/201422

Failure Fraction (Fy) –expresses the combined effects of all components of the

LED module including mechanical failures, as far as light output is concerned. The

effect of the LED could either be less light than claimed or no light at all.

Y = percentage of LED Lamps/Modules no longer ‘operational’ at the end of their

declared life (complete failure or low light output)

E.g. F10 100,000hrs = 10% of LED’s can be expected to have failed by the end of their

rate 100,000hr life.

A mixed Fy is not useful in professional lighting design!


08/10/201423

Parametric failure By - failure of an

operating LED product to produce luminous

flux higher than or equal the luminous flux

relating to the lumen maintenance factor.

For the purpose of this standard the LED

product is an LED module.

For example if we claim L90@100,000hrs,

the By figure relates to the percentage of

LED no longer meeting 90% lumen output.

90

90

90

90

90

90

89

80

60

85

70

90


08/10/201424

Median Useful Life (of LED Modules) Lx – is the length of time during which 50%

(B50) of the LED modules have parametrically failed to provide at least the percentage of

initial luminous flux stated.

L90@ 100,000hrs

is actually

L90B50@100,000hrs

.

90

90

90

90

90

90

89

80

60

85

70

70


08/10/201425

Gradual Light Output Degradation LxBy – gives the opportunity to qualify the time

for a declared gradual reduction in light output for a population other than 50% where

required.

Where By gives the possibility to declare an alternative percentage.

L70B10@ 100,000hrs

.

70

70

70

70

70

70

70

60

70

65

70

70


08/10/201426

L90B50@ 100,000hrs

1 LED module Initial lumen = 1200lm

@100,000hrs we are expecting 90% of the initial lumens

.

@100,000hrs = 1200 x 0.9 = 1080lm

However if we take into account the B50 what we actually

get is 6 LED at 90% output and 6 LED at 50% output.

Therefore @100,000hrs lumen output = (6*90)+ (6*50)

= 840lm

90

90

90

90

90

90

50

50

50

50

50

50


08/10/201427

L70B10@ 100,000hrs

1 LED module Initial lumen = 1200lm

@100,000hrs we are expecting 70% of the initial lumens

.

@100,000hrs = 1200 x 0.7 = 840lm

However if we take into account the B50 what we actually

get is 10 LED at 70% output and 2 LED at 30% output.

Therefore @100,000hrs lumen output = (10*70)+ (2*30)

= 760lm

70

70

70

70

70

70

70

70

70

30

30

70


08/10/201428

Abrupt failure - failure of a LED product to operate or produce luminous flux

Note 1 to entry For the purpose of this standard the LED product is an LED module.

Note 2 to entry The term “complete failure” is commonly used for the same purpose.

Time to Abrupt Failure Cy - length of time which y% of a population of initially operating

LED modules of the same type fail to produce any luminous flux.

E.g. C10 (100,000hrs) means @ 100,000hrs 10% of the LED modules can be expected to

have failed abruptly giving no light output.


08/10/201429

.


Capital Vs Return on Investment

Finally we look at Capital versus Energy.

LED has provided lighting engineers with

more choice than ever but why is there so

much choice?

Here we consider whole life costing of

lighting solutions which would allow

investigation into initial investment over

lifetime savings.

We question do we invest in a low price

luminaire with a short payback or does

paying a premium for a more efficient

luminaire with a longer payback period

provide the best value and best return on

investment (ROI)?

08/10/201430


08/10/201431

Capital Vs Return on Investment

.

Ta=25°C No of LED'sDrive

Current 5700K 12 24 96 108 120 132 144

350mALumen Output 1364 2779 10750 12124 13437 14701 16014

Wattage* 14 26 97 112 123 135 147500mA

Lumen Output 1819 3688 14600 16368 18186 20005 21823

Wattage* 19 38 142 162 179 195 213700mA

Lumen Output 2384 4799 19095 21521 23864 26249 28644

Wattage* 28 55 202 227 252 277 303

“From Specification to Lighting Reality”

ILP Summit–September - 2014

Summary

Make sure data is presented for the correct Ta

Check the how the Luminous Flux is presented, absolute or relative photometry.

Efficacy is expressed in Luminaire lumens LLm/w

CCT, check the lumen output and SP ratio are correct

Is the Ra value correct for the application

Check lifetime claims, lighting designers are interested in LxB10 figure

Failure rate F10 should be accounted for in whole life costs