More on LED

Light Colour

I recently had a look at some of the currently available LED bulbs in my local hardware store. The majority were more or less appalling in light colour. Two clear bulbs (with little light dots stuck on a stick) were green-white. Seven of the frosted LED bulbs were an odd sort of cool purple-blue-white despite being marked as “warm-white”. Only a few were even remotely warm-white for real. Many of the LED bulbs were also very dim, and useful for absolutely nothing.

But I have to say that the 12 W Philips Master LED-series MyAmbiance bulb (Swedish consumer test winner 2011 and predecessor of the improved U.S. L-Prize test winner) looked very incandescent-like from just looking at the lit bulb there in the store, and it was nice and bright without being glaring.

But as I didn’t feel like spending €70 (!) on a lamp I’m not sure I’ll like at home, or how long it will last or retain its original colour and brightness, I have yet to see how it looks in a home environment without all the lit surrounding lights. Maybe I’ll buy one later anyway just to satisfy my curiosity.

It was very heavy though… Probably because of all the electronics inside and the amount of metal needed for heat sink.

Philips online catalogue specifies it as Warm White, CCT 2700K, CRI 80, approx 825 Lm, and 25 000 hr rated average life.

Left: an unlit Philips 12 W Master LED
Right: a lit Philips 10 W L-Prize winner
Source: youtube screenshot

As can be seen in the latest CALiPER test by U.S. Department of Energy on Home LED Replacement Lamp 2011 (Table 1.), very few of the 38 different lamps had a CCT (correlated colour temperature) under 3000 K. I think in replacement lamps it needs to be actually a bit under the ~2700 K of incandescent lamps to look as warm – if that is the aim.

Colour rendition

In photography and cinematography, the colour rendering capacity of the light source is of essence. Here is an example from a highly informative ScreenLight & Grip newsletter:


CRI hi&lo (ScreenLight & Grip)

The newsletter author comments:

I also wouldn’t try to light a table-top food/product shot with LEDs either. As is readily apparent in the shots above, because of their limited color rendering capability, food presentation that will look vibrant and colorful to eye, under LEDs will tend to look a little dull on camera. By comparison a full spectrum daylight source such as HMI or LEP will capture the vibrant colors. Likewise, I wouldn’t try to mix LEDs with a uniform continuous light source, such as a studio lit with tungsten fixtures. If caught in isolation, their color deficiencies will be quite noticeable and unacceptable in comparison to the tungsten.

Colour shift

Even the unusually good looking warm-white colour of Philips’ next best LEDs may not last, as the light is not produced by RGB (mixing of red-green-blue light to produce white, which is also an option in LED) but by blue diods behind a yellow phosphor mix coating on the inside of the yellow parts of the bulb.

It is common for phosphor-based light sources that the phosphors that produce the red part of the spectrum get consumed first, turning the light more and more blue or green as it ages, and LED phosphors are no exception.

LED colour shift
(image from SceenLight & Grip)

There is an electronics store in Stockholm (Kjell & Co) where the counters are lit from above with rows of LED reflector lamps, of which some have been replaced. The result is exactly like the example in the top right photo above. Not very attractive. And the whole atmosphere of the store feels more like a morgue than someplace I love to go shopping, even though I like their products.

In ‘cheaper’ (well, comparatively speaking) LEDs, such as those mentioned above, this colour shift can be seen fairly soon.

Possibly, this may be avoided in the L-Prize bulb which has some red diodes inside and not just blue, so it will not be dependent on the red-producing phosphors to stay warm-white?

And if you have wondered why colour uniformity even in new warm-white LEDs seems so hard to achieve, it depends not only on the phosphor mix but also, apparently, on the diods themselves. The ScreenLight & Grip e-newsletter explains it well:

Given the irregularities inherent in the manufacture of the semiconductor wafers from which White Phosphor LEDs are stamped, the LEDs in a production batch are all slightly different. In a mechanized testing procedure, they are sorted and grouped together into bins according to their flux and color. Binning has been refined over the years, and these days the tolerance of the best binning systems allow barely perceptible differences between LEDS from a selected bin. The difference in color between two sources is quantified using what is called the “MacAdams ellipse.” A MacAdams ellipse defines the distance at which two colors that are very close to one another first become distinguishable to the human eye as different colors. As illustrated below, for a given point of color on the chromaticity diagram, the MacAdams ellipse defines the contour around it, where the colors that surround the point are no longer indistinguishable from that of the point.

Unfortunately, even the L-Prize testing committee finds colour variations acceptable for home lighting LEDs, as can be seen in the Technical Review document [credit to Freedom Lightbulb for finding a copy of it!] under the point Color maintenance (emphasis added):

Variation among submitted samples are well within the allowed limit. However, Philips asks for less tight tolerance for the production lamp, proposing a 0.006 variation limit. Although there are some concerns about users perceiving a slight difference in color appearance between lamps, Philips indicates that a ∆u’v’ of 0.006 is the maximum boundary and 90% of the production lamps will fall within a 0.004 ∆u’v’boundary. Given that an absolute tighter tolerance is a trade-off with cost, the TSC believes this tolerance to be acceptable. 

In the latest CALiPER test by U.S. Department of Energy on Home LED Replacement Lamp 2011 with samples of A19 bulbs, G25 globes and MR16 and PAR20 reflector lamps, colour variations were between 0.0010 and 0.0100! Not that I’m quite sure what such numbers translate to visually, but if Philips and the prize committee sees a variation of 0.004 or 0.006 something to haggle over, then it certainly sounds significant.


The ScreenLight & Grip e-newsletter also explains the difficulty in getting LEDs to dim as easily and beautifully along the Planck curve as incandescents do.

Another problem is that, while it is relatively easy to put a dimmer on an LED, and blend two different color LED chips to achieve variable color mixing, as we saw above it is quite a different matter to track the color so that it remains on the black body locus at every point from daylight balance to tungsten balance. Maintaining a specific color temperature at a high CRI while dimming is made even more difficult by virtue of the fact that temperature in the LED changes when they are dimmed. Change in temperature shifts output wavelength as well as efficiency, and different LED chips change efficiency at different rates and at different temperatures. For these reasons, a more complex approach to dimming is required in order to control all these factors.

And as noticed by Save The Bulb, even the best LED replacement bulb available on the market today, Philips Master LED (same family as the L-Prize LED bulb) doesn’t dim very well (emphases added):

The [LED lamp] got cooler in appearance and the perceived colour rendering became much worse casting a gloomy grey in the space.

[T]he lamp also suddenly went out about half way through the travel of the dimmer’s slider, the GE lamp dimmed right down to the minimum setting. What was really alarming was that the [LED] lamp would not switch on at dimmer settings below about 70%. This was a serious problem in this location where three way switching was installed.

Really I am somewhat disappointed in a product that cost me $19.75 and does not work reliably at less than full power even when it claims to be dimable. Solutions such as this must be made fully compatible with existing wiring infrastructure.

Dimming incandescent

GE Reveal fulll on and dimmed
(photo: Save The Bulb)

Dimming LED

Philips LED fulll on and dimmed
(photo: Save The Bulb)

My comments:

1. Note how the LED, even when turned on fully, is not quite as warm as the blue-enriched GE Reveal incandescent lamp.

2. Note also how the LED (being a directional light forced into an omnidirectional bulb) mainly illuminates the ceiling area and leaves much of the corridor in the dark, whereas the incandescent lights up the whole space more evenly.

3. And finally, how the incandescent dims nicely along the Planck curve and gets warmer without losing light quality, as the light from all natural light sources always behaves. Whereas the LED light indeed turns into a gloomy blueish grey.

The L-Prize committee technical review says:

Capable to at least 20% dimming of maximum output without flicker.

Although the initial dimmers designated by Philips did not appear to be widely available and testing conducted by PNNL with a wide variety of dimmers showed several issues with the subnitted lamps, Philips redesign of the driver for the production lamps will meet these criteria. Philips has also stated that they will reveal any known incompatibilities in their product literature and on their website. 

That doesn’t sound overly reassuring…

Instead of searching Philips already hard-to-navigate website for info on which dimmers may be incompatible, I think I’ll just avoid putting any Philips LED bulb in any of my dimmable fixtures (I’ve already fried one dimmer when I thoughtlessly tested a CFL). I believe the reason some CFLs and LEDs are made dimmable is primarily to make them work with existing installed dimmers without blowing the circuits, not to actually be dimmed.

Power Factor

According to the CALiPER test mentioned earlier, Home LED Replacement Lamp 2011, Power Factor on tested lamps ranged between 0.38 (!) and 0.99.

And the L-Prize testing committee found it perfectly acceptable with 0.70 PF even for the best LED lamp, when used at home:

…and explains why (my emphasis):

Power Factor for submitted lamps meets both criteria. However, the production lamp design does not meet the L Prize criteria for commercial applications, but all lamps will be greater than 0.7. The TSC finds this acceptable as it understands the lower power factor is a trade off with more universal dimming performance and that an important early market for the L Prize lamp is the residential market. 

But this bulb is absolutely useless for dimming! So what’s the point in trading away better PF for a desired function that it flatly fails on?


The excellent German site Argumente für die Glühbirne [thanks again to Freedom Lightbulb for the link] reports that consumer magazine Ökotest (‘Eco-test’) issue 11/2011, found LEDs to flicker! How much varied between brands. Flicker in the 11 test specimens was:

2 LEDs extremely pronounced
5 LEDs pronounced, but also on higher radiofrequency
1 LED pronounced
3 LEDs weak, but also at higher frequencies

Rare elements

From another page on the Glühbirne site (translated by google):

The 17 rare earth metals include cerium, dysprosium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium.

Rare-earth metals are not rare. The name comes from the fact that they originally found in rare minerals were. Some of the rare earth metals are more common in the earth’s crust than other elements, but larger deposits of suitable minerals are rare indeed.

China dominates the market for rare earths.

2010 was the share of world market at 97 percent.

2011 China has reduced the export volumes for the umpteenth time.

For some metals (yttrium, thulium and terbium which are required for CFLs) there is a complete export ban.

Following referenced links to Send Your Light Bulbs To Washington, which in turn quotes a Light Bulb Choice blog post, quoting and

Huge Price Increases Underway from Lamp Manufacturers: The impact of rare earth metals shortages

There is a rapid, emerging shortage of rare earth metals, a primary component used in the manufacture of fluorescent lamps – principally phosphors. Phosphors are transition metal compounds or rare earth compounds of various types. The most common uses of phosphors are prevalent in green technologies such as batteries, magnets, computer hard drives, TV screens, smart phones, and energy-saving light sources – and fluorescent lamps.

The problem with the supply of rare earth elements is that demand has skyrocketed over the last decade from 40,000 tons to 120,000 tons. Meanwhile, China, who owns the monopoly of rare earth minerals has been cutting its exports. Today, it only exports about 30,000 tons a year – only one-fourth of the world’s demand.

In a U.S. Department of Energy report dated December 14, 2010, it was noted that ”it is likely to take 15 years for the U.S. to mine enough rare earth minerals to shake its dependence on China.”

With China currently controlling up to 97% of the world supply of rare earth metals, it shouldn’t come as a surprise that they’ve been imposing tariffs and severe export restrictions.

More from Journal of Energy SecurityThe Battle Over Rare Earth Metals

Also, as reported in a 2-page article in New York Times: Earth-Friendly Elements, Mined Destructively with sad pictures of ruined landscape, there is nothing environmentally friendly about how rare earth metals are mined in China (emphasis added):

Here in Guyun Village, a small community in southeastern China fringed by lush bamboo groves and banana trees, the environmental damage can be seen in the red-brown scars of barren clay that run down narrow valleys and the dead lands below, where emerald rice fields once grew.

Miners scrape off the topsoil and shovel golden-flecked clay into dirt pits, using acids to extract the rare earths. The acids ultimately wash into streams and rivers, destroying rice paddies and fish farms and tainting water supplies.

On a recent rainy afternoon, Zeng Guohui, a 41-year-old laborer, walked to an abandoned mine where he used to shovel ore, and pointed out still-barren expanses of dirt and mud. The mine exhausted the local deposit of heavy rare earths in three years, but a decade after the mine closed, no one has tried to revive the downstream rice fields.

Small mines producing heavy rare earths like dysprosium and terbium still operate on nearby hills. “There are constant protests because it damages the farmland — people are always demanding compensation,” Mr. Zeng said.

“In many places, the mining is abused,” said Wang Caifeng, the top rare-earths industry regulator at the Ministry of Industry and Information Technology in China. 

“This has caused great harm to the ecology and environment.”

Many mining operations are even run by gangsters:

Half the heavy rare earth mines have licenses and the other half are illegal, industry executives said. But even the legal mines, like the one where Mr. Zeng worked, often pose environmental hazards.

A close-knit group of mainland Chinese gangs with a capacity for murder dominates much of the mining and has ties to local officials, said Stephen G. Vickers, the former head of criminal intelligence for the Hong Kong police who is now the chief executive of International Risk, a global security company. 

Telling illegal ore from legal does not seem possible:

Western users of heavy rare earths say that they have no way of figuring out what proportion of the minerals they buy from China comes from responsibly operated mines. Licensed and illegal mines alike sell to itinerant traders. They buy the valuable material with sacks of cash, then sell it to processing centers in and around Guangzhou that separate the rare earths from each other.

Companies that buy these rare earths, including a few in Japan and the West, turn them into refined metal powders.

Besides these rare earth metals and a stunning amount of electronic components (commented on by FreedomLightbulb), LEDs also contain, depending on colour, other elements, such as indium, gallium, aluminium or zinc.

Plus arsenic, lead, nickel “and many other metals”, as reported earlier (emphasis added):

Oladele Ogunseitan, chair of UC Irvine’s Department of Population Health & Disease Prevention [] and fellow scientists at UCI and UC Davis crunched, leached and measured the tiny, multicolored lightbulbs sold in Christmas strands; red, yellow and green traffic lights; and automobile headlights and brake lights. Their findings? Low-intensity red lights contained up to eight times the amount of lead allowed under California law, but in general, high-intensity, brighter bulbs had more contaminants than lower ones. White bulbs contained the least lead, but had high levels of nickel. 

With incandescent lamps, it was just a glass bulb, a tungsten filament and an aluminium base…

…that produced an easily & beautifully dimmable, naturally warm light of the highest quality, power factor and all the rest. 

More on LED issues from ABC: Are LED lightbulbs worth the extra money?



  1. lighthouse said,

    August 27, 2012 at 8:16 pm

    I quite like the look of the Philips LED lamp in its own right
    But of course the dimming and other issues, including price of course.
    Dimming is overlooked in many ways eg how it saves energy with incandescents, and how it would hardly be used with CFLs/LEDs for the reasons you mention, and also the fire risk with CFLs in dimming circuits made for incandescents (circuits in which the CFLs dont work properly anyway)

    Thought that was the Halogenica meal being lined up….
    I was quite impressed!

    • halogenica said,

      August 29, 2012 at 12:24 pm

      Haha, I can’t cook.

      But you’re so right about the dimming. That is never taken into consideration when talking about incandescent energy use. (I think I mentioned it in one of my summary posts as a factor to consider.)

      Missed the fire risk though. You don’t happen to have a link handy?

  2. Trichromatome said,

    August 27, 2012 at 11:43 pm

    Not judging his research, but O. Ogunseitan’s press release was spun to get attention from the mass media and the chemically illiterate public. Who would want to spend taxes or tuition on that kind of university?

    Just yesterday, I had to chase off another gang of mutant fluoride-headed preschoolers who were chewing away on the family car’s tail lights. I had already gotten rid of all the glass in the household and windows because babies might break it, and bleed to death. Discarded all teflon and Al pans, long ago, sure, better safe than sorry. I now resolve to take all my Ni-containing pots and Cu-containing Ag cultery to the hazmat collection site, and gladly pay extra for the disposal of those biohazards, too. It’s all SO DANGERous out there, and I’m so glad that Big Government and Minding Professors are doing their best to save us!!!

    • halogenica said,

      August 29, 2012 at 12:35 pm

      Haha, I have to agree with you on that. As I think I mentioned in my original post: not very likely to be a health risk in everyday use the way CFLs are, as most people do not pulverise their LED lamps at home. And I find coloured LED lamps ending up in toddler belly highly unlikely. Even if lead tastes sweet, its hardly on the outside of the mini bulbs, and they are usually fastened to a Holiday light string or some other product and not just laying around on the floor for babies to chew.

      The context I mentioned it here was just that LEDs do require more materials to produce than incandescent lamps, including rare and sometimes toxic elements, which may be mined in a harmful way, and probably not recycled after use.

      These are not the characteristics a ‘green’ lamp should have, should it?

  3. December 21, 2012 at 1:22 am

    […] With LEDs, the consumer gets a poorer quality, dimmer light with often strange light colour, dimmability problems, suboptimal colour rendering; extremely high purchase pri… (up to €70 for a decent looking 60W replacement that will change colour and become dimmer with […]

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