engineer-in-wonderland
Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...

An Engineer in Wonderland: Green chandeliers don’t sparkle

cc-chandeliers.jpg I was speaking to someone from a big heritage organisation the other day, and learned that there is a hunt for ways to cut the power consumption of chandeliers. These, apparently, were usually designed specifically for incandescent bulbs, or have been converted to them from either candles or gas. At 10 lm/W, incandescent bulbs are not very power efficient, but they weigh very little and most importantly their optical output allows the chandelier to sparkle. LED and compact fluorescent bulb replacements have been tried, but they failed the all-important sparkle test.

Compact fluorescent bulbs are also too heavy, and LEDs are also too blue – apparently ‘flattening’ colours in the room.

Colour coding LED info
blue-dot.jpg Driving into the blue
brown-dot.jpg Organic – grow your own
green-dot.jpg Green chandeliers
black-dot.jpg Into the black?
red-blue-green-dot.jpg Display Trilogy
white-circle.jpg Headlight glare
yellow-dot.jpg Phosphorous
red-dot.jpg Sensing light
grey-dot.jpg Grey area
An alternative look at the hues
and shades of LED technology

So far the best solution is halogen bulbs, which provide the necessary sparkle while cutting power consumption in half. They also weigh little and retrofit easily. It is the failure of LEDs in the sparkling department that surprises me, so I guess those tried had some form of enclosure that converted the diodes to area emitters. The too-blue problem is certainly surmountable by avoiding blue+phosphore LEDS, as the Mona Lisa is lit by a multicoloured array of LEDs in the Louvre. So it looks like there may be a niche in the market here for a retrofitable LED chandelier light source. And just for once I doubt accurate spatial colour mixing, that bane of luminair designers, would be a problem amongst all those sparkles. If anyone has any ideas on this subject, you could make a big heritage organisation very happy. Let me know by leaving a comment via the fields below. Alice (special contributor) By the way, the title An Engineer in Wonderland was inspired by the 1967 book ‘The Engineer in Wonderland’ by Professor Eric Laithwaite: champion of the linear induction motor. (Picture – kimba, under Creative Commons Attribution Licence)

Tags: diodes, halogen bulbs, light source, Luminair, mona lisa

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6 Comments

  1. 'Alice'
    September 28, 2009 12:35

    Thanks for all the information and corrections.
    It looks like leds are still not the answer for chandeliers that have to light a room.
    ‘Alice’

  2. Ian Benton
    September 21, 2009 12:19

    Dr. Dan Doxsee is just plain wrong about halogen lamp efficiency. Efficiency varies as the square of filament temperature, and the whole point of the halogen lamp is that the addition of halogen gas, and the use of a quartz envelope allows the filament to operate at a higher temperature without failing: thus it operates at higher efficiency.

  3. Auntie G
    May 31, 2008 18:29

    Humm, interesting discussion you’ve got going here Alice. As someone also from a large heritage organisation I would just like to add one or two points. Firstly the chandliers we deal with are not always units converted from gas or candles, (which were designed for a light source that was ‘aimed’ upwards and not downwards), some were created at the very beginning of electrified lighting circa 1890 – 1900. Today they are not used for more than anything more exacting than decorative lighting, certainly not for working by.
    We are investigating alternatives to tungsten lamps and are due to visit Philips at their offices in Guildford to see samples of their halogen-capsule-in-GLS bulb. These may be a ‘happy medium’ between the highest efficiency types i.e. LEDs and compact fluorescent and some of the poorest, i.e. the soon to be banned (maybe) tungsten “bulbs”.
    Conservation Architects are often some of the main obstructors (?) to coverting older style luminaires to more efficient light sources. However I do have to defend them in saying that some modern lamps are just too bulky or heavy for flimsy, delicate older style luminaires.
    We really hope that Philps have come up with something useful.
    The HEI (High Efficiency Incandescent) lamp that GE have come up with might also be of interest (30lm/W) but that’s not due out until 2010. Whispers are a foot of it achieving 60lm/W for 2012.

  4. Alice
    March 20, 2008 16:53

    I have been in touch with our ‘large heritage organisation’ which owns many properties with chandeliers.
    Any replacement for its standard conventional light bulb, it appears, has to be a one-for-one replacement as in most cases the chandeliers are a couple of hundred years old.
    They have been converted from gas mantle or candle to electric, so the positions of the lamps are dictated by the construction of the chandelier and no extra positions can be added.
    The search for an off-the-shelf direct replacement for its conventional incandescent lamps lasted many months before a special halogen replacement was identified.
    It looks like the easy LED options were exhausted during the search for a replacement.
    One of its engineers has contacted Electronics Weekly, responding largely to Nichia’s Dr Dan Doxsee it appears.
    ………………….
    “I generally agree on the points made but you have to remember the function of a chandelier and that of a display case are very different.
    This particular organisation uses LEDs to light collections in display cases that are sensitive to UV light.
    A chandelier needs to provide a certain light level to maintain safe circulation or working environment for the occupants.
    So the replacement LED would need to achieve a similar light output to the incandescent lamp as It would not be possible to install more LED lamps than the chandelier has positions for incandescent lamps.
    For this reason and the colour problems with using off-the-shelf LEDs; Philips Lighting has developed a special halogen replacement lamp.
    The replacement compact halogen lamp integrated (CHL-i) has a lamp life of 3,000 hours, about three times that of an incandescent lamps.
    It has an efficacy of 20 lm/w (for a 30W frosted globe), almost twice that of an incandescent lamp. A slightly higher efficacy is achieved with a clear globe.
    And it is UV and mercury free, which has an advantage over compact fluorescents.”
    ……………..
    ‘Alice’

  5. Dan Doxsee, Ph.D.
    March 19, 2008 13:08

    I think there I a lot of misinformation in that article. Frankly not much was accurate.
    Let me address each point.
    Sparkle: Yes incandescent bulbs offer sparkle due to them being point sources. Yes fluorescents have far less sparkle because the light comes from a big surface area, not a point source. However, LEDs offer excellent sparkle also as they are very small point sources. It is possible the author is referring to an LED retrofit bulb (many LEDs inside a thing made to look like a bulb) and that the bulb had a diffused cover which would reduce the sparkle. However, LEDs on their own offer excellent sparkle. As proof, many makers of lighting systems for jewellery display cases have converted to LEDs from fluorescent or halogen. Halogen is inefficient, run hot, and only last ~1000 hours. They have good sparkle, but have to be frequently replaced and there is an issue with people burning themselves. Fluorescent is far more efficient, but the quality of light is poor and there is little sparkle. LEDs offer excellent sparkle, high efficiency, and long life. Also, LEDs can be offered in a variety of colour temperatures from warm white (yellowish light like from an incandescent or halogen, which is good for displaying gold) to cool white (less yellowish, more bluish, which is good for displaying silver and diamonds).
    Halogen efficiency: Incandescent and halogen have about the same efficiency (~10-12 lumens per watt) so replacing incandescent with halogen cannot possible reduce the power consumption by half.
    LEDs are Too Blue: The white LED was invented by Nichia in 1996. For the first 6 years only cool white (bluish white) was available. But since 2002 warm white LEDs have been available. These have the same colour temperature (shade of white) that incandescent and halogen do. If the chandelier had ‘too blue’ LEDs in it then this is because the manufacturer of the chandelier did not choose warm white LEDs. It is not a technology limitation at all.
    I hope this helps.
    Dan Doxsee, Ph.D.
    Senior Sales Manager
    Nichia America Corporation

  6. March 16, 2008 21:34

    Yes, you are certainly right about the colour aspects. The blue LED+yellow phosphor “cool” white LEDs will be too blue. Mixes of coloured LEDs are used to illuminate objects with the correct colour temperature and colour rendering index range, but these are in projected light systems to illuminate an object. If the same multiple coloured LED approach was made in a chandelier, it would sparkle, but with very noticeable discrete colours, rather then the colours only being separated by refraction through the glass pendants of the chandelier.
    Also, your observation of the area of the light emitted is also correct. Compact fluorescent bulbs have large, diffused envelopes and a number of LED approaches to try to replace incandescent sources use diffuse envelopes. In order to sparkle, the sources needs to be bright and small, so tiny shafts of light are reflected and refracted through the glass/crystal chandelier pendants, giving the sparkle effect.
    Therefore, an LED chandelier solution should most likely use the latest “neutral” or “warm” white LEDs to give a more acceptable lower colour temperature and a better colour rendering performance, due to their wider wavelength spreads. Also, LED source would need to be configured to maintain a similar illumination level and directionality as the halogen source, but retain the small extended source size to enable the all important, but elusive, sparkle.
    Polymer Optic would be please to advise further on the optical configuration for any specific developments or applications you may have. I’m sure we can put the sparkle back!