I recently picked up a couple of LED light bulbs that are starting to become more popular in Japan. After comparing a few different options from various major manufacturers, I settled on the “40 Watt” (450 lumen) bulbs made by Panasonic. The main draws for me were the relatively high efficiency (more lumens per watt) compared to other LED bulbs, and the fact that they emit a warmer orange color rather than the harsh bluish light typical in CFLs. Another draw was the fact that these bulbs are rated to last 40000 hours, or about 5x as long as CFL bulbs, which could reduce waste.
On the other hand, at around $30 a pop (2380JPY, to be exact), they’re pretty expensive as far as light bulbs go. Are they worth it? I decided to run some numbers, comparing the LED bulb I got to a traditional incandescent 40w light bulb, as well as “40W”, “60W” and “100W” CFL bulbs. The results are in this spreadsheet below (see the original document on Google Docs).
- klmh – “klmh” stands for “kilo lumen hours”, and can be thought of as the total amount of light emitted, if it were possible to gather light over time and put it in a box. One klmh equals the amount of light emitted by a 1000 lumen lamp over 1 hour, or a 1 lumen lamp over 1000 hours. Technically, a lux is a better unit with which to measure total light emission, but that information wasn’t available (while lumens were) so I used Kilo-Lumen-Hours to compare bulbs of different brightnesses.
- Power costs – I used $0.15 per kWh. Actual energy costs vary from around $0.10 to $0.20 in the US. See prices for September 2010. Calculating the cost of energy for off-grid systems is much, much harder, and would vary widely from system to system, so that is left as an exercise for another day.
- Annual usage – To calculate “costs over 5 years”, I assumed an average 5 hours of usage per day, or 9125 total hours of usage.
- Total costs – The “total cost” calculations combine the amortized cost of the bulb with estimated energy costs (again, at $0.15/kWh).
I tried to compare the bulbs from a wide range of perspectives, and ended up with all sorts of numbers. I’ve highlighted the ones that I think are relatively informative, but, as you can see, some bulbs do better in some comparisons, and do worse in others. In other words, there’s no clear all-around winner.
Efficiency – In terms of efficiency, the “40W” LED bulb (65.22lm/W) was bested only by the “100W” CFL bulb (67.33lm/W). In reality, the LED might perform a little worse, because LED lamps have more directed lighting patterns, so despite what the lumen rating is, the actual total amount emitted may be less than CFL bulbs. As a side note, it was also interesting to see that the efficiency of CFL bulbs improved with increase in wattage. I think this is because fluorescent lights become more efficient the longer they are, and higher wattage CFLs simply have longer tubes.
Cost – If all you care about is having a light bulb –any light bulb regardless of brightness– in a socket, LED is by far the cheapest option. Even though the upfront cost of the bulb is considerably higher than the alternatives, the additional expense is offset by the bulb’s long lifespan and low energy usage.
On the other hand, LED bulbs are relatively dim compared to the brightest CFLs, and if you must have lots of light, CFLs are cheaper for the amount of light you get. This last point is important. Even though a 26W CFL bulb has 1/10 the cost of a 6.9W LED for the same amount of light, the simple fact that it uses more than 3.5 times as much electricity can not be overcome. Having a 26W (“100W”) CFL in that socket will cost you more than twice as much as using a 6.9W (“40W”) LED bulb. But if you must have that much light, it is cheaper to use one “100W” CFL bulb than to use multiple “40W” LED bulbs.
More is more, less is less
Retailers often try to get consumers to buy more stuff by offering lower per-unit costs when purchased in bulk. While buying in bulk may lead to real savings, such deals can also be a pitfall that leads to excessive consumption and spending. The question to ask is, “Do I have to alter my behavior, in order to take advantage of this deal?” If the answer is “yes”, it is best to stay away from bulk purchases. For example, let’s say a grocery store has a deal on ice cream, such that if you buy 2, you get 1 free. The question is “Would I eat more ice cream if I bought 3?” If the answer is “yes” (and let’s be honest now), just buy one, because one is still cheaper than two, in absolute terms. On the other hand, if you’re dealing with something like toilet paper where abundance probably won’t lead to higher consumption, buying in bulk might actually save you money.
The same applies for lighting. If you can get away with less lighting, it will save power and money. Don’t let the illusion of better “value” trick you into consuming more unless that is really what you want, because you will pay more for it. Using one “100W” CFL bulb for 5 hours a day over 5 years will cost an estimated $38.18, while a “40W” LED bulb used for the same duration will only cost $16.29, even when factoring in the cost of the bulbs. Yes, you get less lighting, but you get less for less, while more costs more.
Lighting accounts for 12% of domestic electricity consumption in the US, and I would argue that that makes it a ripe target for reduction. While current trends are towards improving efficiency, Jevon’s paradox warns us that efficiency may in fact increase consumption. If that is true, it seems to me that the true path to reduction is, well, to reduce. That is, rather than merely swapping 60W incandescent bulbs with “60W” CFL bulbs, consider using “40W” bulbs. Instead of having area lighting consisting of 5 or 6 bulbs, consider having 5 or 6 individual lamps located strategically, so that only localized areas that actually need lighting are lit at any given time. Or, for that matter, turn those lights off entirely, and go to bed early. Artificial lighting can interrupt our natural circadian rhythm, leading to sleeping disorders and other maladies. So going to bed early and getting some extra sleep can save your health and the planet. Now that’s what I call a good deal.