How a Philips light bulb uses blue LEDs to produce white light

Figure it out yet? Any idea what’s going on in the image above? Here’s a hint: that’s a Philips LED bulb in action.

There’s no two ways around it: many potential buyers have been turned off by the yellow cap pieces on some LED bulbs. These bulbs might be efficient, increasingly affordable, and last for upwards of 25,000 hours, but what the heck is with that day glow yellow?

Those three yellow pieces on the top of certain LED bulbs are the remote phosphor… and they are not there just because some misguided designer thought they looked cool. These are a crucial part of the design for one reason, which the image above makes abundantly clear: the bulb uses blue LEDs. What the remote phosphor does is convert that blue light to a shade that is more acceptable to what we expect from indoor lighting. In this case it’s 2700K, or warm yellow.

So, as you probably guessed by now, the image shows a bulb that is missing one of its remote phosphor panels. The phosphors that are in place are doing exactly what phosphors do — emit light through the process of luminescence. What this means, functionally, is that the yellow pieces get the blue light and convert it into exactly the shade of light that Philips is looking for.

As for the “remote” part, that just means that the phosphor is not connected to or built into the LEDs. This is done for a number of design reasons, including the placement of the highly directional LEDs and to prevent multiple shadows from forming.

When one of the yellow pieces is removed — be careful of your eyes if you try it at home — you can clearly see that the light from that third of the bulb is a sort of royal blue. The rest of the light goes through the phosphor and is emitted as a shade of white.

And those neon yellow plastic pieces? When the bulb is on you can’t see them at all, which is why the remote phosphor isn’t as big of a problem as you might think when seeing a bulb on the shelf.

As you can see in the smaller image, Philips’ AmbientLED uses three sets of six blue LEDs, plus the remote phosphor, to generate its light. The company’s LED Prize bulb, in order to take efficiency to the next level, uses a different mix. That bulb uses three red LEDs, two blue, and then another shade of blue. It’s a more complex operation but it helps the L Prize winner get to an excellent 94 lumens per watt, where the normal model gets about 65.

And why use blue LEDs at all? Why not just use LEDs that produce a color that we like? This gets pretty complex, but basically it comes down to something predictable: blue LEDs are more efficient than other colors.

If you were interested in this post, you might want to check out my book, LED Lighting: A Primer to Lighting the Future. It’s available from O’Reilly (DRM-free), Amazon, iBooks, and others.

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Philips’ new 100W-equivalent LED bulb runs on just 23W

The Light Fair convention kicks off in Las Vegas this week so there will be any number of related announcements coming soon. Lighting giant Philips is starting things off early with the announcement of their 100W-equivalent LED bulb, the AmbientLED 23W. The model produces 1700 lumens, putting it at a very respectable 73.9 lm/W.

The unveiling comes shortly after Philips’ L Prize bulb was made available to consumers. That bulb currently sells for about $60 and is a more efficient light source, capable of 94 lm/W. The two use similar designs, for example both take advantage of remote phosphor, but the AmbientLED 23W (it will be called the EnduraLED in non-consumer applications) is brighter and lacking in some of the performance characteristics of the L Prize winner, including luminous efficiency and color accuracy.

While it’s not the first 100W-equivalent LED bulb to be produced, the new AmbientLED will be an early release into this segment of the market and it marks the clearing of a major hurdle for the company. One of the limits to LED bulb adoption has been the lack of availability of high lumen bulbs — it’s easy enough for consumers to replace a 40W or 60W bulb with an LED-powered model, but replacing a 75W or 100W incandescent with an efficient light source still requires a CFL. With this release Philips will have 40-, 60-, 75-, and 100W-equivalent LED bulbs available.

The bulb will be dimmable and the color temperature will be 2700K (warm white), making it a reasonable choice for household lighting. The color accuracy (rated by the color rendering index, or CRI) will be 80, which is a reasonable number, but not particularly high. It would be fine for general use but too low for times when high color accuracy is needed, as in an art gallery or photography studio. This is the same CRI as the company’s popular 60W AmbientLED, so they likely share a phosphor material and LED setup, while the L Prize winner has some subtle tweaks to it. For example, it uses a mixture of red and blue LEDs, as opposed to just blue ones.

Philips has not announced the lifetime of the AmbientLED 23W, but it has noted that the bulb will last “up to 25 times longer than a traditional incandescent” which can be taken to mean 25,000 hours. That’s a standard number for LED bulbs and the requirement for Energy Star qualification, which Philips expects the new bulb to achieve.

Philips’ 100W-equivalent bulb will be available some time in the fourth quarter. Pricing has yet to be announced, but it will likely be well over $30.

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Philips’ L Prize bulb is efficient, expensive, and available

Perhaps you recall that, a few years ago, the Department of Energy put together a competition called the L Prize. This was designed to promote LED lighting by giving a big cash prize, and some great PR, to the lighting manufacturer that was first able to produce a bulb capable of meeting certain stringent criteria. In August 2011, lighting giant Philips won part of the L Prize and received a cool $10 million for their trouble. What they produced was an “A” bulb, which fits in a standard household socket, yet is light-years ahead of the incandescents that it’ll be replacing. That bulb is finally available for sale and one can be yours for the low, low price of $60.

The L Prize winning bulb (yes, it’s an self-congratulatory name, but it’s better than the 10A19/LPRIZE-PRO/2700-900 DIM) might be initially expensive, but it has some outstanding specifications that will make it cheap over the long term. Consuming just 10W, it’s able to produce 940 lumens, making it a good deal brighter than your average 60W, and it should last for 27.4 years if you use it three hours a day. The warranty alone is good for 36 months or 15,330 hours, whichever comes first. It’s a 2700K bulb, which means it’s a “warm white” shade, not like those ugly blue-tinted CFLs you bought a few years ago.

If you’ve purchase lighting recently you might have noticed the Philips AmbientLED 12.5-Watt A19, which looks a whole lot like the L Prize winner, but is available for $24. The L Prize bulb is immediately recognizable because of the three neon yellow sections (the remote phosphor) on its top, but past that the two look a whole lot alike. What’s sort of difference does the extra $36 get you? The AmbientLED consumes 12.5W and produced 800 lumens, meaning that the more expensive bulb is over 33% more efficient in terms of lumens-per-watt. Of course the AmbientLED is a perfectly fine bulb so you might think of this as paying more for the performance model, the way you would with a luxury sedan.

Sooner or later some rebates will kick in and this $60 bulb will be in the sub-$30 range, plus its efficiency gains will trickle down to the more affordable models. Until then, it’s a nice bulb and a (relatively) cheap thrill if you are into lighting or the energy market.

And when I write that it’s a cheap thrill, I’m speaking from experience — I actually purchased one and have been using it. I wasn’t able to do much scientific testing but I did find it to be noticeably brighter than a normal 60W-equivalent bulb. I measured the power consumption to be about 8W, so either my testing tool is off or that 10W number is just reference point that none of the bulbs will go over. I’ve just started using it though, so I won’t fully know the color temperature (it seemed a bit cool) or power consumption until the bulb has had some time to break in, which normally is considered have happened by the 1000 hour mark.

This tiny piece of lighting history is available today from places like Bulbs.com and EFI.org. It will be more widely available on Earth Day (this coming Sunday).

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