FOCUS
by
Geoff Archenhold
93
TECHNOLOGY
LED
DRIVING RESPONSIBLY
BRITISH GOVERNMENT LED ADVISER, DR. GEOFF ARCHENHOLD,
EXPLAINS WHY LED DRIVER RELIABILITY WILL BE ESSENTIAL FOR SSL
TO SUCCEED
The editor at mondo*arc has Association in the UK.
received quite a few requests and 3. Can you show me all the
comments on manufacturers’ standard safety test reports
claims regarding the reliability of for all components?
LED systems and so I have de- • Quickly reduces sub-standard
cided to devote the next few SSL LED products – provides the end
articles to LED system reliability users with the assurance that the
and more particularly LED drivers products, especially LED drivers,
and their reliability. are safe!
Before I launch into lots of
technical maths and the theory 4. What lifetime testing
of system reliability I have been information can you provide
Figure 1: The high performance Cool, Neutral and Warm
asked to reproduce the five as assurance?
white LED arrays from Bridgelux in Star and Square package
simple quality questions which • If no test data – do you be-
formats.
I presented at the recent IALD lieve the warranty? Most compa-
conference at The ARC Show. nies will not have any lifetime test
The five simple questions allow data for 50,000 hours but if they
array and operated at a nomi- leading the way in discussing
anyone in the lighting supply could demonstrate something
nal current the lumen output of “hot” lumen performance data
chain to quiz their LED suppliers which is a few thousand hours of
the array was always difficult to then I hope the trend will be for
to ensure they end up only pur- lifetime data then this will ensure
compute due to the temperature other LED lighting manufacturers
chasing quality products. If your that they have done some reli-
differences seen in practice from to follow suit so that designers
LED supplier cannot provide the ability engineering
those found in the LED data- and specifiers can believe with
information then it is likely their
sheet. This meant that the major- certainty the LED datasheets.
products are purchased from an 5. What IPR or licenses
ity of LED fixture manufacturers Bridgelux has launched a series
unreliable source which could come with your products?
would simply compute the lumen of high power and high efficiency
mean problems for your projects • LED IP space is complex so
output of their LED fixture by LED arrays (See figure 1) that
in the future. The five questions check if they have a licence or
calculating the number of LEDs break the traditional price/per-
are as follows: they have their own IPR, other-
within the fixture and multiplying formance ratios of LED systems
wise the products you are selling
it by the minimum “cold” lumens by placing more than one high
1. Which LED and Phosphor could be infringing on someone
figure per LED. Of course this is power LED die within a pack-
does your fixture use? else’s technology which could be
totally incorrect and has resulted age. Although not the first LED
• Ensures the product has a very costly in the future!
in many lighting designers get- manufacturer to do this, others
quality LED to start off with and
ting very excited over claims by include ENFIS, Edison Opto and
give the end user a high assur- To start off this month, I thought
manufacturers regarding the indeed OSRAM, the products
ance that the LEDs will have a I would mention what I hope will
light output of LED fixtures and are specifically tailored for high
good lumen maintenance perfor- become a trend from LED manu-
then getting very disappointed volume lighting applications and
mance. facturers who publish datasheets.
when they observe most LED are highly cost effective. The
• If the supplier cannot answer A major breakthrough has been
products do not measure up to arrays come in two formats - a
this question convincingly then be achieved as the LED manufac-
their claimed light output due star or square tile configuration
very careful as the LEDs may be turer, Bridgelux, has been the first
to the “cold” lumen calculations - which have options of Cool,
low cost and not perform well for to publish the performance data
falling short from real life operat- Neutral and Warm White from
long. of their LEDs when operated at
ing conditions. 400 Lumens up to 2000 Lumens
what could be considered “Real”
To my knowledge the first LED fix- dependant upon system configu-
2. Please show me the in- temperatures rather than the
ture manufacture to provide real rations.
dependent photometric test unrealistically low temperatures
lumen performance data was IST Table 1 (see over) highlights the
report? usually quoted at 25oC.
Lighting with their DL LED down- various light output flux charac-
• Proves real performance of Up until now LED datasheets
lighter range which measured teristics for the LED arrays and
the LED lighting fixture in op- referred only to the lumen char-
the performance of their products importantly there are several
eration. Most quality LED fixture acteristics of a single LED die at
at standard operating conditions columns covering the minimum
suppliers will use reputable test 25oC in short pulsed mode (so
rather than the “cold” lumen “cold” lumen values as found in
laboratories such as BSI, 42 called “Cold Lumens”) so when
figures. With the advent of LED other manufacturers datasheets
Partners, PC(UK) or the Lighting the LEDs were formed into an
manufacturers such as Bridgelux such as Philips Lumileds and
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