A Guide to Specifying LEDs
PhotonStar™ supports and provides
data in accordance with ‘The Guide
for Specifying LED Lighting’ produced
by the Lighting Industry Liaison Group
(LILG) consisting of industry leading
organisations
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PhotonStar™ supports and provides data in accordance with ‘The Guide for Specifying LED Lighting’
produced by the Lighting Industry Liaison Group (LILG) consisting of the organisations below.
Also many of the requirements are being mirrored in the International Electrotechnical Commission,
IEC LED Modules for General Lighting Performance Requirements IEC/PAS 62717, and
Particular Requirements for LED luminaires IEC/PAS 62722.
A chain is only as strong as the weakest link
An LED luminaire is in many ways more complex than a traditional lighting fixture, in that many system
components and operating conditions require tighter control to provide optimum performance. It is an
electromechanical system that includes, in addition to the essential light emitting source, provisions
for heat transfer, electrical control, optical conditioning, mechanical support, and protection, as well as
aesthetic design elements. Because the LEDs themselves are expected to have long life, all of these other
components, adhesives, and other materials must be equally long lived, or, to the extent they are not, they
will limit the system lifetime.
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Specifying LEDs
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& Lighting
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Factors effecting the design of LED luminaires
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Data Required for Specification
Specifying LEDs
Ambient Temperature
All key measured data for the luminaire should be presented for an ambient temperature of 25ºC.
Data Required for Specification
•
Initial Luminaire Lumen Output L100
•
Photometry at L100
•
Light Output Depreciation Category (1, 2 or 3)
•
Luminaire life L(x) (where x is the percentage of L100 at the declared life)
Photometry
•
Failure Fraction F(x) (where x is the percentage of failures at L(x))
Photometric data is available in two formats. Absolute Photometry does not require the use of a separate
•
Colour Temperature at L100 and any shift 25% of rated life
•
Colour Rendering Index Value
photometric data is supplied.
•
Colour Rendering Index Value Shift
PhotonStar quote absolute photometry of LED luminaires conducted according to IES LM-79-08
•
Luminaire Electrical Characteristics (total power consumed and
(15ºC for Exterior luminaires).
Initial Luminaire Lumen Output
This is specified in the performance tables for the product as L100
lumen output for the light source. Relative Photometry requires the LED package flux to be quoted.
Both methods produce the same result. The manufacturer should state the format in which the
other key electrical parameters)
Photometric Measurements of Solid-State Lighting Products.
Lumen Depreciation
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The lumen depreciation rate is judged by the light output at 25% of rated life (with a maximum duration
of 6000hrs) compared to the initial output. The depreciation classification is:
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Light output > 90% of initial
Cat 1 / Code 9 / IEC/PAS 62717 Ed1
Light output > 80% of initial
Cat 2 / Code 8
Light output > 70% of initial
Cat 3 / Code 7
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PhotonStar™ quote both
Lumen Maintenance (%)
Code
≥90
9
These are effectively the same thing
≥80
8
expressed in different ways.
≥70
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Under IES / PAS 62717 this is quoted as follows:
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e.g. Cat 1 / Code 9.
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Explanation of Specification Parameters
Lifetime Lx
Specifying LEDs
Lifetime is defined as “The length of time during which a LED light source, LED module or LED luminaire
Colour Temperature at L100 and any shift
at 25% of rated life
provides more than the claimed percentage ‘x’ of the initial luminous flux, under standard conditions.”.
The initial colour point (x & y) of the LED and the colour temperature derived from it or bin class related to
A LED product has thus reached its end of life when it no longer provides the claimed percentage of the
C78.377-2008 where colour temperature values are recommended as 2700K, 3000K, 3500K, 4000K,
initial luminous flux, Lx. Life is always published as combination of life at claimed lumen maintenance and
5000K, 6500K.
failure fraction, Fy applying at the time of reaching the claimed percentage of the initial luminous flux, Lx.
A reliable luminaire manufacturer will indicate the basis of these projections. It should be noted that if a
product contains a good quality LED light source that has LM-80 data available and the LED module or
luminaire maker calculates lifetime data based upon the LM-80 data, this represents an extremely good
start in ensuring that the LED module or luminaire could be reliable. For LED modules and LED luminaires,
Luminaire Colour Rendering Index
The initial Colour Rendering Index (CRI) of a luminaire is measured. Generally CRI of greater than
80 is appropriate for interior general lighting.
the lumen maintenance curve can also be effected by the combined attributes of all components of a light
A second measurement is made after a total operation time of 25% of rated life (with a maximum
source/luminaire as described in Section 1. LED modules and LED luminaires have life testing carried
duration of 6000hrs). The measured CRI values shall not have decreased by more than 3 points from the
out to 6000hrs.
rated CRI value for initial CRI values and 5 points from the rated CRI value for maintained CRI values.
For general lighting applications, it is recommended to define lifetime as “The length of time it takes an
Further details on this guide can be found on websites of the organisations that endorse it.
LED module or LED luminaire to reach (depending on the application) 70% of its initial light output (L70).”.
For decorative lighting applications, it is recommended to define lifetime as “The length of time it takes
to reach 50% of its initial output.”. Lifetimes quoted according to L70 projected test at 6000hrs or 25%
of total lifetime at a 95% confidence level, defines the abrupt failure or statistical confidence of the data.
i.e. where light output is 70% for 95% of the population.
Failure Fraction (Fy)
published in combination with lifetime (Lx)
This is the percentage ‘y’ of a number of LED light sources of the same type that have reached the end of
their individual lives where ‘y’ designates the percentage (fraction) of failures. For LED modules with drivers
this failure fraction expresses the combined effect of all components of a light source/luminaire.
Failure fraction should be declared at the lifetime Lx and can only be based on testing up to 6000hrs
together with statistical predictions. For general lighting applications this should be less than 10% (F10).
The majority of catastrophic failures will be associated with LED driver electronics.
There are additional tests implied in this measurement including temperature cycling, thermal endurance
and supply voltage switching tests, however these are product specific.
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MacAdam Ellipses
MacAdam ellipses refer to the region
on a colour chromaticity diagram
which contains all colours which are
indistinguishable, to the average human
eye, from the colour at the centre of
the ellipse. The contour of the ellipse
therefore represents the just noticeable
differences of chromaticity.
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ANSI/IEC Standard
ANSI recommends that
lamp manufacturers
stay within a ‘7-step’
ellipse. This means
that, given a certain
CCT target point
(in this case 3000K)
on the CIE diagram,
the lamp can deviate
within the boundary of
a 7-step ellipse.
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Data Required for Specification
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Specifying LEDs
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Colour Temperature Tolerance
PhotonStar™ Products
Tolerance (categories) on nominal x & y values measured for both initial and at 25% of rated life
All our luminaires are individually colour (CCT, CIE x, y) tested and serial number logged.
(with a maximum duration of 6000hrs) specified as measured x & y’s within a 1, 2, 3, 4, 5, 7-step ellipse.
Tolerances beyond a 7-step ellipse are considered unacceptable for general illumination purposes.
This is in compliance with IEC / PAS 62716.
PhotonStar™ luminaires have transitioned from ANSI binning (e.g. 3000K ±150K) to a
4-step (e.g. 3000K ±100K) and 2-step (e.g. 3000K ±50K) MacAdam ellipse,
subject to the light engine.
Further details on this guide can be found on websites of the following organisations.
Size of MacAdam
Colour Variation
ellipse centred on the
Category
www.lightingassociation.com
www.lif.co.uk
rated colour target
initial
maintained
3-step
3
3
www.theilp.org.uk
5-step
5
5
www.highwayelectrical.org.uk
7-step
7
7
www.sll.org.uk
>7-step ellipse
7+
7+
T: +44 (0)2381 230 381
www.pld-a.org
www.iald.org
www.photonstarlighting.co.uk
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