PLS 2014: From Specification to Lighting Reality

“From Specification to Lighting Reality”
ILP Summit–September 2014
Emily Bolt – Bid Manager – Public Lighitng
Thorn Lighting

ILP Summit–September - 2014
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2 08/10/2014

“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?
3 08/10/2014

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.
4 08/10/2014

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)
5 08/10/2014

What is the LOR?
LOR = luminaire output
6 08/10/2014
lamp output
Luminaire Output = lamp output x LOR
e.g. lamp output of a 50W HST = 3400lms
3400 x 0.7 = 2380lms

We generally cannot measure LOR
for an LED luminaire therefore it is
recommended that Absolute
Photometric values are used.
Absolute Photometry results in a
7 08/10/2014
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
8 08/10/2014

9 08/10/2014

10 08/10/2014

Lumen packages
The table below shows 3 different luminaires the common denominator is that all three have
a circuit wattage of 28W:
11 08/10/2014
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?
12 08/10/2014

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.
13 08/10/2014

BS5489-1:2013
LED CCT vs. SP Ratio
CCT Luminaire Lumen Output SP ratio
3000K 4967 1.2
4000K 5340 1.5
5700K 5773 1.9
14 08/10/2014

CCT vs Energy Saving
 Based on a standard 10m wide road @ 33m spacing
Lighting Classification
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
15 08/10/2014
P4 P1

“The Truth About LED”
Hen on the Road –March - 2014
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
16 08/10/2014

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
17 08/10/2014

Colour Rendering Index (CRI)
What does BS5489-1:2013 state?
18 08/10/2014

Application Ra Value
Street Lighting > 20
High Pedestrian usage >60
Indoor Lighting 80
Sports Lighting 80+
High End Designer Store 90
19 08/10/2014

“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
20 08/10/2014

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.
21 08/10/2014
TM - 21

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!
22 08/10/2014

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.
23 08/10/2014
90
90
90
90
90
90
89
80
60
85
70
90

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
24 08/10/2014
.
90
90
90
90
90
90
89
80
60
85
70
70

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
25 08/10/2014
.
70
70
70
70
70
70
70
60
70
65
70
70

L90B50@ 100,000hrs
1 LED module Initial lumen = 1200lm
@100,000hrs we are expecting 90% of the initial lumens
26 08/10/2014
.
@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

L70B10@ 100,000hrs
1 LED module Initial lumen = 1200lm
@100,000hrs we are expecting 70% of the initial lumens
27 08/10/2014
.
@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

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.
28 08/10/2014

.
29 08/10/2014

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)?
30 08/10/2014

.
Capital Vs Return on Investment
31 08/10/2014
Ta=25°C No of LED's
Drive
Current
5700K 12 24 96 108 120 132 144
350mA
Lumen Output 1364 2779 10750 12124 13437 14701 16014
Wattage* 14 26 97 112 123 135 147
500mA
Lumen Output 1819 3688 14600 16368 18186 20005 21823
Wattage* 19 38 142 162 179 195 213
700mA
Lumen Output 2384 4799 19095 21521 23864 26249 28644
Wattage* 28 55 202 227 252 277 303

 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

PLS 2014: From Specification to Lighting Reality

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