LED Christmas lights from Philips

Filed under:

The LEDs used in the blue set were not the water-clear type of package. They had some blue tint to them but were otherwise transparent rather than translucent. The white set had clear packages. So I’m satisfied with their fade, chip, peel, and break-resistant claims.

replacement lamp

Tinted package lets you distinguish between colors.

The bulbs in fact do run cool to the touch when lit. Part of that is due to the configuration of the array that keeps only half the LEDs lit at any one time. I didn’t have a good way to test this, but in theory there should be a short time interval as the AC voltage crosses zero volts where no LEDs are lit. If heat from lights is a concern (maybe you’re lighting a freezer case?) then these may appeal to you.

The ultra low power usage claim is actually conservative. Two series strings of LEDs driven at 20 mA should draw 40 mA from the source, and 120V * 40 mA = 4.8W. I didn’t measure actual power used, but this number is conservatively high. Remember, only half the LEDs are on at once, and they are not lit for a full 50% duty cycle. I would expect real power use to be lower than stated.

I was amused by the 76% power savings claim. A quick glance at a package of incandescent mini lights next to these on the shelves seemed to bear it out (48W listed on the set I checked). But what does this mean in real dollar terms? Assume for purposes of illustration that you pay $0.10 per kilowatt-hour of electricity. And assume that you run your holiday lights 24x7 from Thanksgiving through New Years Day (conservatively 75 days, 1,800 hours). The price of electricity to run each string of LED lights would work out to (1,800 hours * 4.8W * $0.10/kWh = ) $0.86. To accept the 76% savings claim, that requires that a reference light set would use $3.58 worth of electricity over the same period. That’s a savings of $2.72 per set per year. At retail the LED set seels for $12. You would need to run it for at least three years to break even under these assumptions. I would expect that not only does your electricity cost less, but that you probably don’t run your lights 24x7.

The 25,000 hour bulb life doesn’t surprise me. That’s well within the normal range of useful life numbers for 5mm indicator LEDs. What’s amusing is that the set comes with two replacement LEDs, probably to offset a consumer expectation that all sets come with replacements. Given the configuration of the LED array, it would be difficult to determine which of the 30 series LEDs had failed. Of course this is a problem with incandescents wired in series as well. I noted that the last LED in each series string was glued into the socket. I couldn’t come up with a good reason why.

These sets do connect end to end, which is handy. The accompanying pamphlet insists that you may only connect three sets that way. Why? It’s a UL requirement. Underwriter’s Laboratory listing is all but a requirement to sell a product on the mass market. UL has not quite caught up to the solid-state lighting industry yet, so you see things like this where the requirement covers all holiday lights. The included fuses are rated 3A. You could string 60 of these sets end to end before you reach 80% of the fuse rating. This may be a compelling feature to some of you.

As for the bulb locking feature, it also serves to ensure you install a replacement bulb with the correct polarity. I found it impossible to remove a bulb from a socket without needlenose pliers. The bulb carriers are very similar to incandescent sets, other than the tab. The LED leads are bent upward to make contact with terminals in the socket, much like an incandescent set. Removing the LED from the carrier requires straightening the leads, which weakens them to the point of breaking. Luckily, there should never be a need to replace a bulb.

Light set lit

The set is lit up.

That covers the manufacturer claims, now my own observations:

I knew I wouldn’t recommend these within two seconds of plugging them in. That’s because of the flicker. 60Hz is right at the edge of perceptibility, so you may not be bothered by it. But the design of these light sets makes the flicker more perceptible than it has to be.

These are too expensive for the value received. They would only save significant money on electricity under very pessimistic assumptions. I figure my electricty rate is closer to $0.08/kWh, and I would operate lights for fewer than 800 hours during a holiday season. That cost savings does not justify the purcahse of LED holiday lights for $12 per 60-light set. 100-light incandescent sets are available for $2 at the retailer where I found the Philips sets. For that cost differential, you could achieve lower total cost even by replacing all light sets each year. The power savings are real, but insignificant compared to the initial cost.

This is a product that would only be interesting to the die-hard LED enthusiast. And ironically, the design makes it less appealing even to that audience. There’s no good way to fix the design problem with these lights. You can’t just add a rectifier because the strings are connected in opposite polarities.

What could have been done to make this an acceptable product? Two main things: 1) a better circuit design with less flicker, and 2) a more realistic price point. I’m confident that over time similar products will be available for lower prices.

Update for 2007: the new models of this product appear to have corrected this deficiency. (I wonder if they read my review?) I have not had time to verify it on my bench, but there appears now to be a rectifier included, which overcomes one of my biggest complaints about the set. Stay tuned for further updates.

Page: 1 2

[prev: Light bulbs waste power]
[next: Forbes: China will lead solid state lighting revolution]