Extreme Dimming

Report
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Extreme Dimming
Presented by FAB Controls Ltd
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Introduction
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Jeremy Turner -Managing Director – FAB Controls Ltd
We are controls consultants, designers and commissioning service providers to the
commercial lighting sector focusing on addressable lighting control systems, daylight
saving and automated emergency testing.
Alan Tulla – Technical Editor Lux Magazine
Lux magazine is the official publication of the Lighting Industry Association and is the
smart, sensible magazine for lighting decision-makers.
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What am I here for?
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We aim today to help you understand some of the challenges of dimming retrofit LED
lamps.
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What do you mean retrofit lamps?
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These are lamps that can fit into existing light fittings.
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These lamps replace incandescent lamps.
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Why don’t these lamps just dim?
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Well we are trying to bang a square peg into a round hole!
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It will fit in the end but there is always a bit left over.
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To help you understand lets start with some basics.
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A – The Incandescent Lamp
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The incandescent lamp has been with us since the 1800’s. Light is is produced by a
small piece of wire know as the filament, this is suspended inside a glass bulb
containing an inert gas.
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When an electric current is supplied to the lamp the filament gets hot and produces
light. These lamps are very inefficient and most of the energy put in is lost as heat.
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Energy lost = Money down the drain.
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B- How do we dim the Lamp
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To dim an incandescent lamp we reduce the electrical energy supplied to
the filament.
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The filament doesn’t get as hot and less light is produced.
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A 10 % reduction in power will give a 35% reduction in light output.
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To reduce the electrical energy we use a phase cut dimmer.
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C- How does a dimmer work?
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To best understand how a dimmer works we need to know what the mains
supply looks like.
On our live screen you can see the mains supply here at LUX Live.
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This is one complete 50 Hz mains phase.
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A dimmer cuts off part of this phase either at the beginning ( leading edge )
or at the end (trailing edge).
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The next two slides show each dimming type, the blue trace is the mains:
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1) Green Trace = The Leading edge dimmer output
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2) Brown Trace = The Trailing edge dimmer output
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1- Leading Edge - Dimming
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2- Trailing Edge - Dimming
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What do we know so far?
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An incandescent lamp produces light from a piece of hot wire.
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If we put less energy in the wire runs cooler and less light is produced.
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We reduce the energy going in to the hot wire, using a phase cut dimmer.
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Dimming incandescent is putting a round peg in a round hole it just works.
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What’s all this talk of square pegs?
The Light Emitting Diode (LED) – retrofit Lamp
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An LED is what's called a "solid-state lighting" technology, or SSL.
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Instead of a piece of wiring being heated up and light being omitted, light is emitted
from a semiconductor. .
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Just like your mobile phone you cannot just connect the LED to the mains and expect it
to work.
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There will need to be a power supply (know as a driver) to convert from mains to the
desired voltage the LED requires.
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With your mobile phone the charger is the power supply.
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With a retrofit lamp the power supply needs to fit into the base of the lamp.
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I still don’t get the square peg!
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We now know that an LED requires a power supply, a power supply is normally
designed to take a known voltage and produce a stable fixed output.
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We know that a phase cut dimmer reduces the mains voltage with the expected effect
that the Lamp should reduce its output.
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The square peg!
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To dim LED we have to try and design a power supply that will vary the light output of
the LED based on the reduced mains voltage being supplied by a phase cut dimmer,
with very little space to house this circuit.
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There is no performance standard for dimmer and or LED lamp manufactures.
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The net result is that each and every manufacture can design the LED driver to their
own specification and each and every country has a slightly different way to do it.
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Many of the dimmers you will encounter when trying to fit retrofit lamps will
have been designed such that the incandescent lamp forms part of the dimmer
stabilisation circuit.
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HELP – What can I do?
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In the next session Alan and I will run through a few of the common LED retrofit issues
you may have seen and the possible solutions.
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This section will be split into three parts:
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Lesson 1 – Mains Lamps
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Lesson 2 - Low voltage Lamps
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Q&A
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During each demonstration the mains sine wave from our dimmers will be shown on the
live screen.
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Channel A shows the incoming mains supply for reference.
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Channel B shows the output from our live dimmer.
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Lesson 1 – Demo 1
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A common issue seen with LED is flickering
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This is normally a dimmer issue
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Here we have a 50w Incandescent(Halogen) lamp
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You can see this is flickering, this is due to insufficient load on the dimmer.
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Look what happens when we add extra load to the dimmer. - Using a Lutron synthetic
load.
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The dimmer is brought into its normal operating parameters and we can see the lamp is
correctly controlled and our sine wave is now clean.
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Lesson 1 – Demo 2
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Demo 1 showed us that minimum load can be a problem.
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This is not always the case.
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Lets repeat the same experiment this time with a budget LED.
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Despite its lower wattage the driver circuit in this LED performs well with this dimmer
and is able to simulate the dimmers minimum load requirements.
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Technical Tip One
Always test the LED’s and Dimmer as a set.
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Lesson 1 – Demo 3
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Now lets look what happens when we mix LED’s from two different manufactures.
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Here we have a good quality GU10 LED its an excellent LED and well suited to most
dimmers.
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As you can see on its own it performs well.
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Add another LED from a different manufacture.
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Wow what happened, did anyone order disco lights?
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This is due to the different driver designs in the base of the lamp.
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Technical Tip Two
Always use LEDS of the same type and manufacture on one circuit.
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Lesson 1 – Summary
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All the lamps in Lesson 1 have used a GU10 pin base and are directly mains fed
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If you follow some simple rules you can normally find a lamp and dimmer that will work
together.
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If you are going to retrofit LED its always a good idea to replace the dimmer at the same
time.
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If you are using a dimming system check to see if the manufacture provides a
compatibility chart, listing your proposed LED.
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Always use a manufacturer who provides a dimmer compatibility chart.
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Always check how many LEDS can be used on the specified dimmer.
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You don’t want to be the guinea pig
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Lesson 2 – Low voltage Lamps
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If you thought the issues we had in lesson 1 were a problem its about to get much
harder.
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GU 5.3 or as most of us know them MR16 lamps use a transformer to step down the
mains voltage to 12 volts
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Typically the transformer has been designed with the lamp forming part of its
stabilisation circuit.
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When it comes to retrofit lamps these do not perform the same way and the
transformers tend to fail.
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Lesson 2 – Demo 1
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A common issue seen with MR16 LED is flickering, popping and general poor
performance when dimming.
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A number of well known manufactures don’t make MR16 dimmable LED’s for this
reason.
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We are using a top top of the range MR16 led for this test.
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This LED was voted by Lux magazine as “Best for Quality of Light”.
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What’s going on?
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If you look at our live screen you will note the trace is a mess.
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This is all caused by a mismatch between the lamp and the transformer.
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To get this lamp to work we are going to have to change the transformer.
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A typical transformer will require a minimum load of 20 watts.
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Lesson 2 – Demo 2
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When using dimmable MR 16 LED you will need to use a zero load transformer.
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This is a transformer that can operate with the very low load of an LED lamp, from zero
watts up to the rated maximum.
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We can now see with a zero load transformer and our top quality lamp that things are
much better.
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The live screen still shows that things are not ideal.
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If we connect an extra lamp it should now all work fine.
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Technical Tip Three
With MR 16 LED the transformer , lamp and dimmer all have to be matched.
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Lesson 2 – Summary
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When using MR 16 you will normally have to change the transformer and the lamp
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The performance of an MR 16 Lamp comes down to the transformer and dimmer.
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Not all MR 16 Lamps will dim with all transformers
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Always use a manufacture who provides a dimmer and transformer compatibility chart.
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Always check the number of transformers and LEDs that can be used on the specified
dimmer.
TOP TIP
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If you are going to change the transformer, why not change the lamp holder and use a
mains GU10 Led.
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Conclusion
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We are now coming to the end of our session.
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We hope you have learned something or at least rested your feet.
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We hope you take away the following tips:
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Always test the LED’s and Dimmer as a set
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Always use LEDS of the same type and manufacture on one circuit
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With MR 16 LED the transformer , lamp and dimmer all have to be matched.
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Always use a manufacture who provides a dimmer compatibility chart.
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You don’t want to be the guinea pig
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Questions & Answers
www.fabcontrols.co.uk
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Thank you to:
www.fabcontrols.co.uk

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