Dimmable LED down lights

Our kitchen is currently lit with 10 × 50 watt tungsten lamps.  Yes: that's a total of 500 watts.  Which is utterly obscene and I feel distinctly uncomfortable just thinking about it1.  We want to replace these tungstens with LEDs, hence reducing the power required to light the kitchen by a factor of 10 or so.  We have several requirements:

• Must be dimmable down to 5% or 1% (some only dim down to 60%)
• Must produce enough light to fill the kitchen
• Must produce a warm, cosy light
• Must produce a light with a high enough colour rendering index to mean that skin looks like skin and not like pale plastic

Dimming LEDs requires a fundamentally different approach to dimming incandescent lamps.  LEDs require a constant current at all times.  The best approach to dimming LEDs seems to be to switch them on and off very rapidly (100,000 times a second - far too fast for your eye to perceive a flicker).

Some manufacturers produce MR16 LEDs which do work with normal TRIAC dimmers and transformers (the sorts of dimmers and transformers used for tungsten lamps).  I presume these LEDs must include some clever electronics which first "decodes" the dimming signal from the normal dimmer and then uses this signal to drive a proper LED driver.  For example, the Philips Dimmable MASTER LED 4W MR16 24° from ledbulbs.co.uk for £18.99 does a reasonable job of dimming from a normal dimmer.  But it's expensive and it flickers a little and only dims down to about 30% of max output.  This isn't good enough: we want something that dims down to 5%.

The lamps I've tried include:

• 6W Dimmable MR16 / GU5.3 12V Warm White 120° LED Bulb Super Bright at 310Lm from eCrater.co.uk for £9.41
• Philips Dimmable MASTER LED 4W MR16 24° from ledbulbs.co.uk for £18.99
  • Lovely quality of light; genuinely looks like a tungsten light.  Not a huge quantity of light though.  Expensive! Flickers a tiny but when used with a normal dimmer.  Only dims down to about 30%.  Does not flicker at all when used with a normal (non dimmable) 12v transformer.
• MR16 DIMMABLE 9W LED BULB WARM WHITE CREE CHIP SUPER BRIGHT £7.59 from xclusivesuppliesuk  on ebay
  • Not very impressed.  Flickers when using a "normal" 12v transformer (even when used without a dimmer).  I'll try it with a proper LED driver.
• MR16 NxtGen LED Non-Dimmable (22 piece SMD 5050, 390 Lumens, 50 watts equiv.) from SimplyLED for £11.99
  • 370 lumens (for the warm white) / 5 watts consumption = 74 lumens / watts (which is pretty good)
  • I've bought this non-dimmable light to see if it can be dimmed using a dimmable LED driver
  • Update 24/2/2012: I've now received this bulb.  It is indeed very bright.  But it has a poor CRI.  Skin looks distinctly ghostly when illuminated by this lamp.  Overall it produces quite an "ery" light, even when warmed up with orange lighting gel (CTO 1/4).

LEDs I found while searching but didn't buy:

• Dimmable 4W Low Voltage High Power LED MR16 Warm White MR16 Direct Replacement for £13.99 from energylightbulbs.co.uk
• Savervalue LED Dimmable Spotlight 6W Warm White Light Bulb MR16 12V AC/DC (3 X 2W) 50mm D for £11.99 from saverstore.com
• MR16 Dummable Spot Lights from Light Planet

Attempting to get dimming down to 5%

I think we need to bite the bullet and use a proper "dimmable LED driver", instead of using "dimmable LEDs" in conjunction with normal TRIAC dimmers.  Using "dimmable LEDs" in conjunction with a normal dimmer is pretty ugly from an engineering perspective: the dimmer was never meant to be used with LEDs and the LEDs must therefore each include electronics to handle the LED dimming (e.g. these TRIAC Dimmable LED drivers made by National Semiconductors).  It's better to use "dumb" LEDs in conjunction with an LED driver which can do dimming.  (There's a good intro to dimming LEDs here).

Some dimmers I've found:

• MR16 LED dimmable driver 180 watts, takes 240v input.  "Will operatre between 1 and 25 (6watt) MR16s."  Not clear how it works.  Comes with a dimmer.  £63.95 from SLB.  Dims down to about 1%.

Some other dimmable LED drivers which probably aren't appropriate for my application:

• SLV 464002 - PHILIPS LED DRIVER, DIMMABLE 700MA, 30VA £40.37 from bigwhitelighting.com
• Farnell do loads of LED drivers (not many dimmable)
• RS do lots of dimmable LED drivers.  Search the http://uk.rs-online.com/RS website for "led driver dimmable"
• MeanWell do lots of dimmable LED drivers.
• mr-resistor do some interesting LED drivers (and have a 2 show rooms in London)
• I think this MeanWell dimmable LED driver 12v 60W for £55 might be the one to go for. Dims 100-10%.  I presume the LEDs must be put in parallel.  It runs from mains (hence doesn't require a separate PSU) and can be controlled either using a resistor or a 1-10v input.  So I just need to replace the wall switch with a vairable resistor (with mains switch) and run a control cable up to the ceiling space.
• Or maybe I should use a constant current system like this Philips 75W 0-10V (£95) or this Philips 150W 0-10V (£100).  Both dim down to 10%.  I think I need to use a constant current driver with constant current LEDs.
•  

Variable resistors with switches are available from Maplin.

update 20th Feb 2012:

Oooh, I've just stumbled across some nice-sounding 230v GU10 LED light fittings.  Dimmable from 3-100% from a TRIAC dimmer. 8W.  60lumen/watt for warm white. CRI >83  TC110 from SGSLIGHT.  I've asked for a sample.  I found them through alibaba.com (and there are other lamps on there which dim to 3% or less). 

update 22nd Feb 2012:

Looking for high CRI lamps.  It looks like most LEDs have a CRI of aroun 60-75%, which is pretty poor.  The highest CRI I've found it the CREE LRP38-10L which has a CRI of 92% but isn't available in a package I can use.

I found that RS sell lots of LED lamps including an 8W MR16 LED warm which lamp with a CRI of 90% (and a price of £31!).

update 24 Feb 2012:

• LED magazine buyer's guide
• LED lighting nodes from Earth.org.uk
• AliExpress has a great search facility for lights - this is probably the best place to find LEDs for import from China.  And the site often quotes a CRI figure for the lights.
• Green Building Forum topics:
  • GU10 LED Test
  • LED bulk purchase
  • Buying LEDs direct from China

• 1. Why do we have such a power-hungry lighting setup in our kitchen? We had some work done on our bathroom last year which required the builders to replace the light fittings in the kitchen below the bathroom; I thought the builders would replace the lamps with the original 20 watt tungstens but no, in their infinite wisdom they threw away my old lamps, fittings and transformer and replaced them with 50 watt tungstens.  Humph.