Philips announces a new but strange looking bulb

http://www.slashgear.com/philips-slimstyle-led-bulbs-get-trim-all-round-hands-on-16308930/

Supposedly it will retail next month for under $10 US. That's a good thing.
The bulb design produces a visible shadow. That's a bad thing.
The bulb is huge. That's a bad thing.

I hope this new bulb is simply a precursor to the 200 lumen per watt bulb supposedly coming in 2014.

I wonder what color temperatures will be available? I hope the warmer option is 3000k rather than 2700k. I've found their trumpet-shaped 11w A19 bulbs to be warmer than incandescents and therefore quite limited in use.

What a strange looking bulb.
I have a few dresser lights with clamp on shades. I doubt they would fit the bulb.

they are definitely thinking outside of the box (or bulb?).
I'm stumped as to how they are handling the thermal design, though. The article has this comment:
"Philips' cleverness is in doing away with the heatsink normally required from an LED lamp. That's required some balancing of LED technology and light output with heat; the bulbs in the SlimStyle could be cranked brighter, Philips told us, but then they'd need more cooling, so it's actually more efficient this way."

Doing away with the heatsink is fine as long as the LEDs don't generate any significant heat. I doubt that this is happening, though.
Maybe they are using thermally conductive plastic? I don't know much about it, but had the idea that it wasn't optically transparent/translucent.
Or are they just running the LEDs hot and hoping for a tolerable lifetime?

LEDs can withstand temperatures to 120°C. Most current LEDs are running at 85°C.

Electrolytic capacitors can withstand temperatures to 105°C. But at 85°C the lifetime shrinks to 6,000 hours for continuous running. By moving the LEDs into the loop away from the capacitors the capacitors can run at 60°C. This extends its lifetime to 40,000 -50,000 hours. No need for a heatsink to get rid of heat before it reaches the capacitors.

Philips have been in the forefront of using remote phosphor technology. If they use remote phosphors in the plastic loop the heat generated by stokes losses will come from the plastic directly to the outside air. This reduces the heat generated by an phosphor coated LED.

The LEDs are spread out and seemed to be attached to the ?plastic? of the loop.
This makes it unnecessary to use a heatsink (or the liquid of a Switch bulb) to get heat to the outside. Just through the material of the loop. Others and myself have found the 'plastic' domes of some LED bulbs, especially Philips, have turned out to be glass. (Tap it and they have a dull thunk, not a ringing sound associated with glass. But they break with jagged edges.) If the loop is glass it becomes the heatsink. Even if plastic heat will pass through, just a bit more slowly.

A lot of thought engineering wise have gone into this bulb. Interesting to see how it turns out.

Depends if people find it too weird looking. Or if they have clamp on shades like BLH.

Viewed from the side, It looks a lot like a toilet bowl.

LEDninja said:

LEDs can withstand temperatures to 120°C. Most current LEDs are running at 85°C.

Click to expand...

It's not really a question of what the max junction temperature is. It's more a question of what elevated temperatures do to the lumen maintenance.

LEDninja said:

Electrolytic capacitors can withstand temperatures to 105°C. But at 85°C the lifetime shrinks to 6,000 hours for continuous running. By moving the LEDs into the loop away from the capacitors the capacitors can run at 60°C. This extends its lifetime to 40,000 -50,000 hours. No need for a heatsink to get rid of heat before it reaches the capacitors.

Click to expand...

Thermally isolating the LEDs would have a benefit to the switching power supply. This would allow the light to live long enough to actually notice the LED degradation. Insulating the LEDs by wrapping them in plastic isn't helping them, though, and there doesn't appear to be anything in the design that changes the power being dissipated in the LEDs.

LEDninja said:

Philips have been in the forefront of using remote phosphor technology. If they use remote phosphors in the plastic loop the heat generated by stokes losses will come from the plastic directly to the outside air. This reduces the heat generated by an phosphor coated LED.

Click to expand...

I don't know anything about heat generated by stokes losses. What percentage of a LED's power dissipation occurs in the stokes losses?

LEDninja said:

The LEDs are spread out and seemed to be attached to the ?plastic? of the loop.
This makes it unnecessary to use a heatsink (or the liquid of a Switch bulb) to get heat to the outside. Just through the material of the loop. Others and myself have found the 'plastic' domes of some LED bulbs, especially Philips, have turned out to be glass. (Tap it and they have a dull thunk, not a ringing sound associated with glass. But they break with jagged edges.) If the loop is glass it becomes the heatsink. Even if plastic heat will pass through, just a bit more slowly.

Click to expand...

I wouldn't use the phrase "unnecessary to use a heatsink". The thermal design can't be ignored. Philips may have decided to just accept a short life from the LEDs in order to meet the price point.

Possibly the best interpretation of the design would be to say that they may have mounted the LEDs on an aluminum strip that provides potentially as much surface area as some of the minimal LED bulbs. Covering the aluminum in plastic will certainly hurt it, unless this happens to be a plastic with particularly good thermal conductivity.

Another interpretation would be to say that Philips just assumes that the consumer will stick the bulb in an enclosed fixure, and the bulb will suffer early lumen loss regardless. Why bother implementing a good thermal design if the consumer just covers the bulb in insulation?

What's to say the inside of the "loop" isn't a copper strip anchored to the screw base using the light fixture itself ad a heat sink?

A bit more info on the LEDs(mid power) and the heat sinking material.
http://illuminationinfocus.com/news/4/12/8

mvyrmnd said:

What's to say the inside of the "loop" isn't a copper strip anchored to the screw base using the light fixture itself ad a heat sink?

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It's possible, but it would still be a poor way to get rid of heat. The screw base in the lamp is electrically insulated and not in contact with the ambient air.

Steve K said:

I wouldn't use the phrase "unnecessary to use a heatsink". The thermal design can't be ignored.

Click to expand...

slebans said:

A bit more info on the LEDs(mid power) and the heat sinking material.
http://illuminationinfocus.com/news/4/12/8

Click to expand...

from the article said:

the new Philips design uses some type of thermally conductive material to draw heat toward the flat center of the lamps where it can be dissipated into the air.

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The bulb is rated 60W equivalent 10.5W exactly the same as their current non dimmible 10.5W bulb. The amount of heat generated and have to be dissipated is the same.
In the current bulb the LEDs are in a cluster in the middle of the top of the heatsink. The heat from the LEDs in the center have a hard time getting out because the heatsink is already heated by the LEDs on the outside.
With the new bulb the LEDs are all the same distance from the (rather tiny) heatsink in the middle. This makes for better heat management. If the tube is glass or other fairly good thermal conductive material, then the surface area of the heatsink (tube plus the flat area in the middle) is quite large. The loop is much bigger than the A-19 incandescent.

Steve K said:

Philips may have decided to just accept a short life from the LEDs in order to meet the price point.

Click to expand...

Philips rated this bulb at 25,000 hours. In the last couple of years they have rated most of their LED bulbs at 25,000 hours.
In the olden days both Lumuleds and Cree rated their LEDs at 50,000 hours at 25°C. Then both start rating their LEDs at 85°C.
The companies that still use 50,000 hours follow the time honoured tradition of companies stating SSC-P7 flashlights are 900 lumens. They just print the biggest number they find on the LED manufacturer's website.

Steve K said:

Another interpretation would be to say that Philips just assumes that the consumer will stick the bulb in an enclosed fixure, and the bulb will suffer early lumen loss regardless. Why bother implementing a good thermal design if the consumer just covers the bulb in insulation?

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Packaging usually say "Not for enclosed fixtures". Except for a few companies like Xledia and Switch. We'll have to see what Philips prints on the package of this bulb.

Somewhere else on the packages Philips also mentioned 3 hours per day. I have 2 Philips bulbs fail on me in 6 months. A MR16 in computer keyboard light and a nitelite. Both run more than 3 hours per day.

For me, the biggest question about the design is the thermal conductivity of the plastic(?) that encases the LEDs. My experience with thermally conductive plastics was with material that had a fair amount of carbon fill or metallic fill, and were quite opaque. Some were fairly close to the conductivity of aluminum, which is impressive. They were also fairly expensive. I think the cost savings came from the ability to injection mold the part instead of die casting or machining. Does anyone have any data on translucent plastic that has a thermal conductivity that is within an order of magnitude of aluminum?

I see references in some posts to glass being a good thermal conductor. This may be a relative term, but compared to typical materials, the thermal conductivity is about a hundred times worse:
http://upload.wikimedia.org/wikipedia/commons/1/1e/Thermal_conductivity.svg

It'll be interesting to see how this light is accepted in the market and what the lifetime numbers actually are.

Their use will be compromized by the plastic thermal path, but the two inner areas are asking for two additional heat sinks. Get the ones with the most sharp and spikey fingers available, call the improvement The Bulb Torque Limiter.

I've found a teardown of the bulb:

http://www.designingwithleds.com/sneak-peek-philips-slimstyle-led-60w-replacement-bulb-review/

It looks like the heatsink is just the copper traces on the PCB holding the LEDs. I'm not actually seeing any electrolytic capacitors but the author mentions them- maybe they're on the back side? The tubular components on the PCB near the screw threads appear to be inductors.

If there aren't any electrolytic caps I would expect this bulb to have increased longevity of the driver circuit with the tradeoff of high 120Hz flicker.

That isolated controller board is going to help keep the caps cool. Clever. Here's hoping for higher power designs with heat sinks in the donut hole ...

Gordon

amd20x6 said:

I've found a teardown of the bulb:

http://www.designingwithleds.com/sneak-peek-philips-slimstyle-led-60w-replacement-bulb-review/

Click to expand...

thanks for that link! I'd seen some of Margery's work in the trade magazines, but didn't know that she had this web site. Very nice!

The tear-down did clarify how they are just using a large circuit board to act as the heatsink. It also shows that the plastic housing isn't bonded to the circuit board, so I don't think that the plastic is thermally conducted. I would assume that the plastic would have been overmolded to the board to improve heat transfer if it was thermally conductive.

It is an intriguing design, and it is tempting to just buy one in order to see how long it lives. At $10, it's a pretty cheap experiment.

amd20x6 said:

I've found a teardown of the bulb:
http://www.designingwithleds.com/sneak-peek-philips-slimstyle-led-60w-replacement-bulb-review/

It looks like the heatsink is just the copper traces on the PCB holding the LEDs. I'm not actually seeing any electrolytic capacitors but the author mentions them- maybe they're on the back side? The tubular components on the PCB near the screw threads appear to be inductors.

Click to expand...

The LEDs are on the round PCB on the top of the bulb. Below that is the driver, the elactronic board with lots of goodies. The capacitors are the 2 red squarish things there.

The problem with most older designs is the heat sink goes down and is wrapped around the electronics and after a while the capacitors end up at the heat sink and LED temperature.
In this design the top LEDs are quite far away from the caps. The heat from the lower LEDs are pulled up towards the center of the PCB away from the caps. My concern (and I think Steve K as well) is whether the heat can get past the casing fast enough so the inside does not become an oven and bake everything.

Steve K said:

My experience with thermally conductive plastics was with material that had a fair amount of carbon fill or metallic fill, and were quite opaque.

Click to expand...

What about GRP(glass reinforced plastic). May not compete with metallic fill but the pcb has already pulled the heat away from the LEDs and the case only has to let the heat out over a much wider area.

LEDninja said:

The LEDs are on the round PCB on the top of the bulb. Below that is the driver, the elactronic board with lots of goodies. The capacitors are the 2 red squarish things there.

The problem with most older designs is the heat sink goes down and is wrapped around the electronics and after a while the capacitors end up at the heat sink and LED temperature.
In this design the top LEDs are quite far away from the caps. The heat from the lower LEDs are pulled up towards the center of the PCB away from the caps. My concern (and I think Steve K as well) is whether the heat can get past the casing fast enough so the inside does not become an oven and bake everything.

Click to expand...

They're film caps, so they had ought to be highly tolerant of the heat. My flicker concern stems from their capacitance. They can't possibly have anywhere near the same capacitance of an electrolytic cap of the same physical size.

I agree that it's a good thing that they've designed it with the kind of thermal isolation present here. That and the apparent lack of electrolytics should give the driver board a long life despite the plastic being subpar for heat removal. We'll have to see how well the LEDs themselves hold up.

LEDninja said:

What about GRP(glass reinforced plastic). May not compete with metallic fill but the pcb has already pulled the heat away from the LEDs and the case only has to let the heat out over a much wider area.

Click to expand...

GRP sounds a lot like fiberglass. Glass is about 100 times worse than aluminum in regards to thermal conductivity, and I think I saw that the thermally conductive plastics are about 10 times worse than aluminum. Epoxy is worse than glass, so the best case scenario for GRP would be that it would be just slightly worse than glass. This would make it about 10 times worse than thermally conductive plastic.

I think the worst part of the thermal design for this Philips light is that there is an air gap between the circuit board and the plastic housing. This adds to the thermal resistance between the LED junction and the air. On the plus side... at least there is a moderate amount of surface area on the circuit board, so that does help reduce the overall thermal resistance. Also, we don't know how thick the plastic is. The thinner the plastic is, the lower the thermal resistance. Too bad they couldn't have added some vent holes to allow air to flow directly past the circuit board.

My estimates here are as follows:

Input power: 10.5 watts as stated.
Output: 800 lumens which equates to ~3 watts of luminous flux.
Waste heat total: 7.5 watts
Driver efficiency 85% which implies ~1.5 watts waste heat in the base where the driver is located.

This leaves 6 watts of waste heat distributed among 26 LEDs. That's only 0.23 watts each. It's quite feasible to get rid of that amount of heat on a regular PCB. Yes, the plastic enclosure acts as a thermal insulator, raising the temperature of the PCB and LEDs. However, at 0.23 watts per LED I doubt the junction temperature is much higher than whatever the internal ambient temperature inside the enclosure is. I'd be surprised if it was much over 60° to 70° C. Bottom line, I'll bet good money the junction temperatures are under 85°C. There's a reason why the trend is towards using many surface mount LEDs instead of fewer power LEDs. You distribute the power (and the light) more evenly. Each LED has to cope with far less power. Even though small SMD LEDs don't have as good a thermal path as power LEDs, they're dealing with proportionately less power.

In a few years time metal heat sinking will probably be a thing of the past as LEDs convert 2/3rds or more of their input power to light.