I don't remember LED Christmas lights being prevalent last year, although maybe I just wasn't being very attentive. They seem like they are everywhere now. But why?There are a couple of reasons LED lighting is attractive compared to normal incandescents, with the runaway favorite being efficiency. LEDs also have a longer life than incandescents and, being solid state, are much more durable and temperature resistant. These benefits are offset by a higher cost.
- A 6W LED bulb (actually an array of LEDs) might have a life span of 60,000 hours, over which it will draw about 360KWh. Let' say a quarter per KWh -- a high but convenient estimate -- for $90 of electricity for its life. Bulb cost? Perhaps $50. 60,000 hours for around $140.
- A 60W incandescent, comparable in lumens, might have a life span of about 1,500 hours. Over the LED's life span, that is 40 bulbs drawing a total of 3,600KWh for about $900 of electricity. Bulb cost? For the 40 bulbs, a bit less than the single LED. 60,000 hours for $950.
- Although CFLs aren't manufactured into Christmas lights, they end up a lot closer to LEDs than to incandescents. A 14W CFL, comparable in lumens to the above bulbs, has a life of around 10,000 hours. Over the LED's life span, that is 6 bulbs drawing 840KWh for about $210 of electricity. 6 bulbs might be about $20, so 60,000 hours are $230.
We use strands of mini bulbs on our indoors tree. These are candle-shaped T1¾ bulbs, also sometimes called an M5. The standard incandescent strand has 48 2.5V lights strung in series to match our 120V mains. Such a strand is about 25W, and if you run it flat-out for a heavy month each year (let's say 1,000 hours) you'll eat an electrical bill of $6.25 for 25KWh, still assuming our perhaps unreasonably high electricity rate of a quarter per.
The claims on strands of 50 LED Christmas lights vary, but from what I've seen they look to be about 5W total pull for a strand of 50, with an advertised life of 25,000 hours or more. Such a strand comes out to an electrical bill of $1.25, 20% of our incandescent cost.
The incandescent minis will have a longer life than a larger incandescent in a pristine environment, but given the rough handling that such strands take they often suffer early death. Continuing my made-up numbers, let's say a 2,500 hour life for the incandescent strand, so we'll need 10 of them over the lifetime of the LED strand. At $2 a strand, total incandescent cost for 25 years of use is a little less than $180. A single $20 LED strand racks up a charge of a little more than $50.
Easy math sure is easy. If I stop being concerned about working the numbers out in my head and plug in a more typical electrical rate of 7¢/KWh, our comparison changes to $37 for the incandescents versus $29 for the LEDs. The more the rate drops the less exciting the LEDs become, although I don't think anybody has cheap enough electricity to ever make the incandescents an efficiency win -- over a 25 year period of use, anyway.
LEDs have some other advantages besides cost. They operate at much cooler temperatures, and are unlikely to ever set anything on fire because of their heat. They usually fail by shorting, which means they have a built-in shunt to keep the strand lit when a bulb goes. They are more durable, with no filament -- although actual durability is complex, and there have been consumer reports of these lights dimming with age, corroding leads made of iron or steel, and in general a failure to squeeze the advertised life out of a strand.
Then there is the issue of how cheaply the LED strands are made. Our household sockets give us AC power, which means when we plug our hot new LED solid state lighting into them the bulbs will only be lit half the time unless the manufacturer spends a little extra money on a rectifier. Without a rectifier, the LED strands will have a 60Hz flicker -- some people are insensitive to this, but alas I am not. I haven't seen any LED strand packaging that would give a clue as to whether this issue is addressed or not, but I have seen flickering LED lights.
In any case, I guess it isn't totally unreasonable that LED Christmas lights are everywhere. They aren't totally irrational from a financial sense, since it is likely Christmas will keep rolling around every year for some time to help you make the most of your initial investment.
Before I put away my calculator, though, I want to take a closer look at the 25,000 hour rated life of a 50 LED strand. If we put 3 strands on our fairly small tree and run them constantly, in a week of 168 hours we've got 25,200 lit hours, and should expect to see a bulb failure. So replacement bulbs still won't be a thing of the past. (Failure for LEDs is more typically a very dim bulb than a bulb going dark.)
Some informative sites: Ciphers by Ritter, LED Center, and of course Wikipedia.
3 comments:
So is it really a 25,000 hour rating for the strand or is it a bulb on the strand?
If we put 3 strands on our fairly small tree and run them constantly, in a week of 168 hours we've got 25,200 lit hours, and should expect to see a bulb failure.
Get thee to a statistician. Your assumption that 168 hours on each of 150 discrete LEDs would result in a bulb failure presumes that LEDs fail randomly with a uniform distribution centered around 25,000 hours, but in fact virtually all failures of non-defective LEDs are age-related. I'd expect you could leave your lights plugged in for a few years before you saw a single LED burn out; after that you might start seeing occasional failures such that after 25,000 hours half of the units had burned out. But even LEDs from the cheapest-as-shit Chinese knock-off manufacturer ought to last for thousands of hours unless overheated or fried by a power spike or something.
We have been victims of the "corroding leads" problem, repeatedly.
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