LED Light Bulbs

After celebrating Earth day yesterday by burning a pile of tires I decided to be “green” and purchase some LED light bulbs from Lowe’s today. And by green I mean save some, because they were on sale today for $10 instead of the usual $20 so I picked up some to see how they fare. I like LEDs. They’re very efficient and especially great in flash lights. They’re also pretty much unbreakable though that may not hold true for the rest of the stuff around the LED in the bulb.

Here’s a quick comparison of some of the normal ways of generating light in a house.

Incandescents:

  • Cheap
  • Dim well
  • Instant light
  • ~1.9-2.6% efficient according to wikipedia
  • 750-1000 hr life according to wikipedia

Compact Florescents

  • More expensive than incandescents (unless you’re in CA where they’re subsidized.)
  • Most don’t dim well though some exceptions exist
  • Delay in generation of first light and wait time to full intensity generation
  • ~9-11% efficient according to wikipedia
  • Life reduced by turning them on and off a lot
  • Contains Mercury which results in special cleanup and disposal issues
  • 6000-15000 hour life according to wikipedia

LED

  • Much more expensive than CFL.
  • Most don’t dim well though some exceptions exist
  • Quick light up time. A tiny tiny bit slower than an incandescent in my experience
  • ~8%-14% efficient according to wikipedia
  • 30000 hour life according to wikipedia

Alright, back to the LED bulb after that brief tangent… Here is a picture of the one I picked up from Lowe’s. It’s a Utilitech Pro brand which is Lowe’s home brand. It is made in China and distributed by Feit Electric Company. The box says it has a brightness of 430 lumens, uses 7.5 watts, equivalent to a 40W incandescent, produces light at a color of 3000 K, and has a lifespan of 25,000 hours. Based on 3 hours use per day, it is supposed to cost 90 cents a year and last for 22.8 years. (I seriously doubt that 22.8 yr number. I remember how long CFLs are supposed to last for and what I get out of them. Still maybe I’ll be surprised. I’ll be sure to report back in 22 years.)

Here it is out of the box. The translucent bulb seems to be made out of plastic and the silver thing is a plastic heat sink. (Edit: I thought the heat sink was metal before but believe it to be plastic now)

Color of the light is noticeably whiter than an incandescent and similar to a soft white CFL. Here’s a picture of three incandescent bulbs and the LED bulb in use. Starting from the top and going in a clockwise direction we have the LED, 100W incan, 40W incan, and 60W incan. The 60W bulb is clear so it doesn’t compare well with the others. The package states that the LED bulb has a brightness of 430 lm and wikipedia states that 40W, 60W, and 100W incandescents have a brightness of 500 lm, 850 lm, and 1,700 lm respectively. To me the LED seemed brighter than the 40W and somewhere in between the 60W and 100W bulbs.

Light bulbs also generate heat as a byproduct. This can be a good or bad thing depending on what the temperature outside is. If you’re trying to cool your house then this is problematic but if you’re trying to warm your house then it is beneficial. The heat generation is also nice for keeping ice off of the light if it is outside in a colder climate (an issue in street lights according to something I read once). So, lets look at some temperatures I measured with the thermocouple on my multimeter. The temperatures are in in Fahrenheit and were measured in the fixture shown above after they had been on for an hour. The glass around the lights probably results in temperatures being higher than if they were not shielded but does represent a real world application of the lights. For the incandescent bulbs, front represents the top of the bulb and side represents the fattest part of the bulb. For the LED, front represents the top and side represents the hottest part I could find on the heat sink. For the CFL, represents represents somewhere on the top of the bulb and side represents on the plastic base.

Front Side
LED 100 154
CFL 123 114
40W Incan 136 235
60W Incan 150 275

Clearly, the incandescents put off a lot of heat. The CFL and LEDs don’t show a clear trend though the LED is more efficient. The heating is different over the entire surface of the bulbs so don’t assume it is uniform. For example the temp varied on the heat sink of the LED bulb and I recorded the highest temperature I found.

Now lets look at how much power they’re using. The apparatus pictured below is my “test stand” for measuring the current running through the light bulbs. The double pronged socket is in series with the switch and light bulb so I can measure current. And no by the way, I didn’t construct that for this post. It’s also used to keep from setting old radios on fire when testing them. Anyways, my multimeter is setup to read milliamps and I swapped through the bulbs recording the steady amperage.

Since AC power is in use, things aren’t quite so easy in calculating the power. In AC there is something called the power factor which affects the efficiency of the circuit. When the power factor is 1 all of the energy is used. When it is less than 1 all of the energy is still needed but it is not all used. Please go to wikipedia to read more about it. (Or if you’re an EE or know more about this than I feel free to comment.) For purely resistive loads like the incandescent bulbs the power factor is 1. When reactive loads are present, such as in the LED and CFLs, the power factor drops. I don’t have a way to measure the power factor so I’m going to use a power factor of 0.9 for the LED and 0.6 for the CFL. These values come from these two sources: CFL and LED. I found other sources that back up these numbers. Still I’ll calculate the power assuming a power factor of 1 for all the bulbs and then with the values mentioned above.

Voltage was measured at 124V. The CFL tested was a 13W (60W equivalent) Sylvania. As mentioned before the LED is rated at 7.5W (40W equivalent). In the case of the CFL, the current is the steady value after it rises on startup.

Current (mA) Power (W) Power (W) w/PF
LED 74.3 9.2 8.3
40W Incan 320 39.7
60W Incan 440 54.6
100 Incan 860 106.6
CFL 120.5 14.9 9.0

Based on my results the LED seems to be a little higher and the CFL a little lower than the stated numbers. My CFL has been in use for a while which may explain the lower numbers. It is probably better to focus on the current instead since it is a directly measured required quantity. Current shows that the LED is more efficient than the CFL for the stated equivalent wattage. Both the CFL and LED have a current listed on the bulbs of 175mA and 90mA respectively which I feel backs up my conclusion. (Note: You can use current measurements to compare all kinds of electrical things. For example, that 5 hp vacuum you own really doesn’t make that much power for any useful time. Read the current for a better way to compare it to other vacuums. That 5 hp number is what we call marketing or BS. Same thing. You can only pull 2.5-3 hp out of a 120V socket depending on the breaker.)

Extra tidbits of info:

Common household incandescents are currently in the process of being phased out here in the US. The ban will start in 2012 with the 100W bub and finish in 2014 with the 40W bulb though another jump will occur in 2020. Read more here. So, if you need some you might want to pick them up soon.

For the American made section of this post…some incandescants used to be made here but all CFLs are made overseas. Most of them are made in China. I’d guess that the LEDs will be made overseas and mostly in China as well. Read more about CFL production here.

Hopefully you are now a little more aware about some of the current lighting technologies. I’m guessing that LED bulbs will overtake incandescents and CFLs in the future so expect to see prices on them to continue to drop. So, keep an eye out for them.

PSA: Electricity can be dangerous. I’m sure you’ve seen lightening. That stuff is in your walls just waiting for you to slip up. So, if you electrocute yourself doing anything related to or mentioned within this post don’t say I didn’t warn you. And unlike those TV shows I’m neither an expert or a professional so you should be doubly concerned. On the other hand, if you get electrocuted swapping out a light bulb you probably have bigger issues!

Advertisements
This entry was posted in At home science. Bookmark the permalink.

One Response to LED Light Bulbs

  1. I blog quite often and I genuinely appreciate your content.
    The article has truly peaked my interest. I’m going to take a note of your blog and keep checking for new information about once per
    week. I subscribed to your Feed too.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s