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18 WORKPLACE 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 4 When 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 equivalentsAndrew 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.

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Page 1: Andrew Bissell, director, Cundall Light 4 YeS · Andrew Bissell and Peter Raynham outline the arguments for and against Andrew Bissell, director, Cundall Light 4 ... (LOR) reduces

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.

Page 2: Andrew Bissell, director, Cundall Light 4 YeS · Andrew Bissell and Peter Raynham outline the arguments for and against Andrew Bissell, director, Cundall Light 4 ... (LOR) reduces

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

Page 3: Andrew Bissell, director, Cundall Light 4 YeS · Andrew Bissell and Peter Raynham outline the arguments for and against Andrew Bissell, director, Cundall Light 4 ... (LOR) reduces

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...