Andrew Bissell, director, Cundall Light 4 YeS · 20 workplace lighting LEDs v fLuorEscEnts June...
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Transcript of Andrew Bissell, director, Cundall Light 4 YeS · 20 workplace lighting LEDs v fLuorEscEnts June...
18workplace lighting LEDs v fLuorEscEnts
June 2013 www.lighting.co.uk
Are LED luminaires ready to replace fluorescents in office applications?LEDs have grown in popularity but, when it comes to the workplace, fluorescents are still more prominent. Could, and should, this change? Andrew Bissell and Peter Raynham outline the arguments for and against
Andrew Bissell, director, Cundall Light 4When it comes to assessing the merits
of LEDs over fluorescents in office
applications, we have to be clear about
what we are actually comparing. I don’t
want to talk about replacing a T5 tube
with an LED tube but, if I were, I would
have to say I am firmly against it. Similarly, the concept of
designing for the end user and putting the light where it is most
needed definitely has its merits but is more suited to high-end
fit-out projects so the budget isn’t always available to do this.
So, for the purposes of this debate, I’ll focus on replacing a
modular T5 luminaire with the latest generation modular LEDs.
The latest LED luminaires have clear advantages over T5s. For
instance, a T5 lamp is cylindrical so the light is emitted through
360 degrees; changing this requires carefully designed reflectors
made of highly polished metal. The use of these introduces
inefficiencies however, and the light output ratio (LOR) reduces
considerably. Also the T5 is only available in fixed lengths of
300mm and multiples of that – but with the fixed length comes
a fixed output. With LEDs you have a point source of light;
as such it is easier to control where the light is distributed.
Through the use of a lens we can have a wide, narrow or
asymmetric beam – all with very little loss of light.
Similarly, new materials are now available that deliver a
diffuse light from an LED point source, again, with very little
loss of light. If we want our luminaire to be 450mm long, it can
be – and all without the need to overlap lamps and hope the
contractor has installed the fitting correctly. Furthermore with
LEDs a variety of light output is available; this means we may
have a 600mm long fitting but we can choose low, medium or
high output chips to suit the task in hand. Of course, dimming
can achieve the same effect, albeit using a little bit more energy.
It is because of these advantages that I feel we are now seeing
modular office LED luminaires outperform T5 equivalents. As
manufacturers have come to understand
LED technology and lumens per watt have
increased with LED chips, the manufacturers
have stopped trying to copy a T5 office
luminaire with its twin lamps down the
centre – instead they are making use of the
characteristics of LEDs. Manufacturers are well
aware that a typical office lighting scheme will
have a 2.4m x 1.8m, or 2.4m x 2.4m spacing
“I feel we are now seeing modular office LED luminaires outperform T5 equivalents”andrew Bissell
but, where they previously would fill a box with LED chips until
they delivered an average of 400 lux (with a lot of the light directly
below the fitting), now the chips are angled and positioned so
you get 400 lux across the working plane with a more uniform
distribution and lower glare rating.
But there are caveats. I can’t emphasise enough that the above
observations only hold true when the specifier is confident in the
data. As with any new technology or new application of existing
technology, some manufacturers ‘hit and hope’ and some deliver
quality products that are well tested and for which data is robust
YeS
top-notch ridi’s ArKtIK-ME LED recessed or semi-recessed luminaire has been designed to fit a standard 600 x 600 ceiling grid
and, more importantly, accessible. As a designer, and when using
LED luminaires, you must obtain and check very carefully the data
of the product and each of its components.
Over the years I have seen plenty of T5 office lighting products
that have neither been built to any standard nor been tested.
Recently we questioned the electronic data we had been sent by a
manufacturer who had brought a T5 alternative to market. When
we asked for a copy of the test data that generated the LDT file,
the manufacturer sent us a lovely colour brochure of a test lab in
the Czech Republic and suggested we get it tested ourselves.
Similarly, we all hear figures of 50,000-hour lamp life, colour
rendering indices of >85 (colour quality scale), unified glare
ratings of <19, 120 lm/W, 100 per cent LOR etc. However, what
is required with LEDs compared with other light sources is that
the data needs to be carefully interrogated. Is the 120 lm/W
with 100 per cent LOR the characteristic of the luminaire or the
characteristic of the LED chip on a lab bench? What is the lumen
output at 50,000 hours? What is the CRI (CQS) at 50,000 hours? Is
there a warranty and what exactly is covered?
The data you need to ensure you give
your client a reliable, high-quality, low-
maintenance, low-consumption LED office
lighting scheme does exist; in my view, the
products also now exist to replace a T5
modular office luminaire. But you must
interrogate the data – if a manufacturer is
slow to respond or only provides part of the
answer, you must dismiss those products.
19 LEDs v fLuorEscEnts workplace lighting
workplace lighting new guidance from the Bco p22
June 2013 www.lighting.co.uk
Peter Raynham, The Bartlett School of Graduate Studies and the Society of Light and LightingDespite the hype, LEDs are just another
family of light sources that we can use.
They differ from other light-source
families in their properties and this
makes them good for some applications and less good for others.
In this debate I have the job of bringing up the bad points of
LEDs; before I get stuck in, however, I would like to say there
are many applications in which LEDs are replacing light sources
such as compact fluorescent or tungsten halogen and show a
great many advantages over the older lamp type, provided they
are installed in new luminaires that are designed to take LEDs.
For me, using retrofit lamps in old luminaires is, by definition,
a suboptimal way of doing things. Luminaires designed for
use with LEDs can exploit the properties of this particular
light source and they are able to outperform retrofit solutions.
However, can they compete against linear fluorescent solutions
in offices?
working it riegens’ Illusion LED luminaires are effective in an office application (above), as is future Design’s all-LED installation (below). Andrew Bissell argues that LEDs give designers greater design freedom and newer luminaires provide improved light distribution
My answer is no. On the face of it, LEDs have a number of
advantages over linear fluorescent technology: they are more
efficient and, being small, can be built into a wide variety of
shapes and sizes of luminaires. However, there are a couple of
downsides: they are expensive and they are difficult to make. Just
these two factors give rise to a number of issues that can give the
old fluorescent technology the edge.
Let’s start with the cost. As LEDs are expensive to make,
manufacturers struggle to make them appear cost effective. This
is especially the case in office-lighting applications where the
energy efficiency and cost of replacing fluorescent tubes takes
some beating. For a given area of LED chip, manufacturers want
to maximise lumen output; as such, they push as much current
as possible through the chips, effectively over-running them.
This gives rise to two problems: the efficacy is reduced and
stopping the chip from overheating becomes more of a problem.
This hot running at high current tends to cause problems with
lumen maintenance.
The second issue to do with cost is that to make LEDs appear
to be an attractive proposition, they have to be sold as having
a very long life. The market seems to have settled on a lifetime
of 50,000 hours but, to get there, most LEDs will only be
giving 70 per cent of their original light output. Moreover, this
lifetime claim is based on, perhaps, 6,000 hours of testing and
some educated guesses, so you need to make sure the product
comes with a watertight guarantee and is from a company you
think will still be around in 10 years’ time. Thus, the term ‘L70’
sometimes appears in the small print. So if you are going to
design the lighting properly, you need to use a maintenance
factor that includes this 0.7 lamp lumen maintenance factor –
this means you are likely to get an overall maintenance factor of
somewhere between 0.5 and 0.6. So, in an office space, you have
the choice of putting in a lot of extra equipment or allowing
no
“LEDs differ from other light-source families in their properties; this makes them good for some applications and less good for others”peter raynham
20workplace lighting LEDs v fLuorEscEnts
June 2013 www.lighting.co.uk
The wider debaTe
Derek Burns, lighting consultant, g-leD glasgow, VisionleDIn the past I would have said no. However, I am currently working with a company that has recently replaced 600 x 600 and 1200 x 600 units with LED panels in a working
office. the results are good: colour temperature is good and I myself have used LEDs in various guises in my office and have found the quality of illumination to be excellent. Plus eyestrain seems to be less – I am getting on a bit!
DaViD Mooney, associate, atkinsIf you do a thorough lifecycle costing analysis to Bs Iso 15686-5, LEDs still do not make sense. It is closer than it was but there still needs to be another benefit to make them a preference versus
4x13w t5HE. You need a 600 x 600 LED luminaire to be within £40 for normal maintenance issues to make a difference. If there are high maintenance issues then it can be a lower differential but, remember, you can still change lamps when you clean the luminaire. WIth a lamp lumen maintenace factor of >96 per cent, t5HE outperforms for both L80 f10 or L70 f10. It’s a close call.
paul stearMan, specification Manager, kosnicIn an office where there are 600 x 600 4x18w t8 tubes, you also have the option of removing the [entire] fitting and replacing this with an LED panel. this may be a slightly
the lighting level to fall below the recommended level a few
years down the road.
For a developer who is going to sell the building to
a naive user this might make sense, but for the
building user it could be problematic. If a user
notices that it is getting dark in the office there
will be a large bill to replace all of the lighting; if the
fact goes unnoticed, the chances are that even more will be
lost through loss of productivity.
The fact that LEDs are difficult to make means it is not
possible to make them so they are all the same. As a result
of this, in order to get batches of LEDs that have similar
performance levels, manufacturers have to use a practice called
binning – the LED is tested and allocated to a particular bin
based on its colour, light output and other characteristics. This is
a reasonable way of doing things but if you need a lot of product
from a particular bin you cannot be sure they will be available.
A second issue is that each manufacturer has its own binning
system, which makes it harder to match products across
manufacturers. As such, it is feasible that the lights in a
given office may have noticeably different colours.
The fact that LEDs are expensive and difficult to
make is perhaps just a reflection of where we are in
the current state of LED technology; it is likely that, in future,
LEDs will be both easier and cheaper to make. This will solve
a lot of problems but, for the present, my feeling is that they
do not quite have the edge on linear fluorescent lamps when it
comes to office lighting.
l This discussion is a transcript from a live debate between
Andrew Bissell and Peter Raynham, which took place at an event
that was hosted by the office lighting manufacturer Future Designs
(www.futuredesigns.co.uk)
more expensive option but, in my experience, a new LED panel will emit more light than the existing fluorescent fitting – usually about 15 per cent so, in fact, you may not need as many LED panels.
iain Macrae, heaD of gloBal lighting applications, thorn lighting, presiDent, sll In downlights, spotlights and emergency fittings there is no doubt LEDs have surpassed fluorescents. Having said that,
most sales are still made on conventional light sources based on cost. Where you have a professional customer who understands lighting and is looking for through-life justifications then t5/t16 luminaires are clearly a winner. these are a good light source, easy and cheap to maintain, of little harm if recycled correctly, and have good efficiency and lumen maintenance. While there are LED luminaires that clearly give it a run for its money, you’d be a fool to ignore the good fluorescent options just yet. However, given energy prices and problems with energy supplies going forward, as well as the ability to easily control LED, I would think we are already at the tipping point where LED becomes a real competitor.
Bright young thing GE Lumination’s 600 x 600 LED luminaire
super saver Kosnic’s KLED36PnL can use up to 50 per cent less energy that fluorescent t8 modular fittings
we also asked a selection of our readers whether leD luminaires could replace fluroescents in the workplace...