9 December 2012

These days, it’s all about energy efficiency.

In some countries, you can hardly even buy normal incandescent light bulbs any more. You are left with a choice of slightly more efficient “a bulb inside a bulb” halogen options, or compact fluorescent light (CFL) bulbs.

Well, there are some problems with CFL bulbs, as we shall see.

Now, LED bulbs have made their big debut on the scene. They use even less power than CFLs, and supposedly they are better for the environment and all that jazz.

In some ways, this is true – but at a cost unless you are careful about which LED bulbs you pick.

And, since LED bulbs are so darn expensive, you need to choose wisely. Here’s how…

First of all, you need to understand the underlying technologies we’re dealing with here, and the problems inherent in each. So, let’s start with some brief summaries.

Incandescent Bulbs

Incandescent bulbs are basically your “standard” bulb. Yes, there are halogen bulbs, halogen spotlights, and so on. But for the most part, these are “regular bulbs”.

The good: The beauty of these old bulbs is that they have a Power Factor of 1 (see explanation of Power Factor below).

The bad: They generate a lot of heat in addition to light, and thus they are not very efficient in comparison to CFL and LED bulbs.

Color Temperature: 2700K

Note: Color Temperature is a measure of the color of the light measured in Kelvin – simply put. The sun is about 5800K. At 2700K, incandescent bulbs are more “reddish” (which humans perceive as “yellow”, but that’s a whole other story). Cooler or “bluer/whiter” colors are around 5000K and above. HID headlamps on cars can be between 6000-7000K. Thus, we humans perceive “warm indoor light” to be around 2700K, like a normal incandescent light bulb.

Lifetime: Usually 1000 hours.

Tricks to choose a good one: None

Compact Fluorescent (CFL) Bulbs

CFL bulbs are a smaller version of those big honkin’ fluorescent light tubes that grace most workplaces and school rooms.

The good: They use less power.

The bad: They have a Power Factor less than 1. Many contain mercury, so don’t break one. If you do, open all the windows and get out of the room for a bit. Then clean carefully. Mercury is poisonous. While you’re at it, get your mercury fillings removed, because guess what? Mercury in your fillings doesn’t magically become safe! What a concept, eh? Also, CFLs usually take time to warm up, and deteriorate over time in both intensity and color. Oh, and CFLs are expensive.

Color Temperature: 3000-3500K for modern “warm white” CFLs, 5500K for “cool white” bulbs

Lifetime: Usually 10,000 hours (10 times the life of a normal bulb). This will vary depending on quality. Also, don’t constantly turn CFLs on and off if you want them to last a long time!

Tricks to choose a good one: Pick “warm white” unless you really like that “cool white” look. Other than that, there’s not much to it.

LED Bulbs

LED bulbs are “the new CFLs”.

The good: They use even less power than CFLs

The bad: They can be rather dim. They also have a Power Factor less than 1. According to Energy Star requirements, LED lighting in the USA should have a Power Factor of at least 0.7 for bulb powers greater than or equal to 5W. Less than 5W, and there is no minimum Power Factor. The reason for this is that, unlike CFLs, LED bulbs do not require electronic ballasts and the generation of high frequencies to avoid flicker. But, LED bulbs do need circuitry to turn AC into DC at a lower voltage. The way they usually do this employs Power Factor-reducing tricks. Also, LED bulbs do not like heat! Fortunately, they normally run fairly cool, but in high-heat environments, they can degrade more quickly. And finally, LEDs are highly directional. So, choose a bulb that will emit light in the direction you need. Many LED bulbs that replace standard incandescents shoot all their light straight up, which wouldn’t make a very good bulb for a table lamp if you’re trying to read a book underneath it. LED bulbs are VERY expensive.

Color Temperature: 2700-5000K. Pick a 2700K bulb!

Lifetime: Usually 25,000 hours (25 times the life of a normal bulb, 2.5 times the life of CFLs)

Tricks to choose a good one: First of all, if you’re replacing a spotlight type of halogen bulb that is 50W, don’t even consider any LED spot bulb less than 5W. The estimates on the packaging are kind of useless (like “3W = 35W regular spotlight bulb!” No, it doesn’t.) For all LED bulbs, ALWAYS pick the one with the highest power rating. LED bulbs are notorious for being too dim. This is changing slowly, but still… If you have a choice between a “8W = 100W normal” LED bulb, or a “12W = 100W normal” LED bulb, pick the 12W bulb.

Also, be sure to choose LED bulbs that explicitly state a color temperature of 2700K. Philips makes a line of bulbs that say “Warm white – 2700K”… That’s what you want. Otherwise, you will probably not be happy with the “cool” light produced by the LEDs. Some “warm” LED bulbs are more like 3300K, which still seems more harsh/cool than a CFL bulb with the same color temperature. So, check the Color Temperature! 2700K is your friend.

Power Factor

At this point, you’re probably wondering what the hell “Power Factor” is. If not, stop reading and skip to the last section!

Unless you’re into electrical engineering, don’t go looking for a detailed explanation of Power Factor. It will make your brain hurt. It made my brain hurt, but since I’m an engineer, I just had to grin and bear it.

Instead, just think of it this way: Simply put, Power Factor means how much power is wasted by the bulb.

A Power Factor of 1 means no power is wasted.

A Power Factor of 0.8 means that 25% more current is required by the bulb to do the same amount of real work. But electrical losses are related to the square of the current. If you need 25% more current, you have 1.5 times the losses.

With an even lower Power Factor of 0.7, 40% more current is required to do the same work, and you have about 2 times the losses.

Now, like I said, don’t try to understand all that unless you’re crazy like me. What you really need to take away from the above can be simplified as follows: As the Power Factor decreases even a small amount, the power company must generate more and more actual power in order for your light bulb to emit the same amount of light.

Practically speaking, that might mean that if you have a CFL bulb that says, “13W = 100W normal bulb!”, then since CFLs have a Power Factor of less than 1.0, your “13W” CFL bulb might actually be requiring the power company to generate 22W of actual power.

Okay, this doesn’t seem so bad, right? I mean, I can hear you saying: “22W is still way less than 100W!”

Correct as usual, King Friday!

BUT… And there is always a big but in there somewhere… The more electrical devices with poor Power Factor, the more juice the power companies have to make, because the more “unbalanced” or “inefficient” the whole power transmission scheme becomes. Of course, I am oversimplifying things, but that’s the gist of it.

Aside from light bulbs, computers, motors, computers, clock radios, appliances, and just about ANYTHING that uses electricity will most likely have a Power Factor less than 1… Unless it is an incandescent light bulb, or something very simple like an electric heating element such as those in a hairdryer (which also have motors – oops!)… See what I mean?

So, are you saving energy? Yes. But you are also “unbalancing the grid” more, and that all adds up. Of course, you are only charged for the ACTUAL power your light bulb uses – i.e. 13W. But the power company still has to make that extra 9W to so that your 13W CFL bulb can actually work properly with it’s 22W of “apparent power” – due to its lower Power Factor.

Again, I am oversimplifying, and that is by design. This stuff really can make your head hurt, but I think it’s important to understand exactly what you are – and are NOT – doing when using these different kinds of bulbs.

If everyone gets 4 additional CFL bulbs for 4 new lamps since they use less energy, they might think they are only using 13W x 5 = 65W. In reality, the power company is spitting out 22W x 5 bulbs = 110W.

Oops. So much for “saving energy”. So, don’t go crazy on lighting just because you’re using CFLs or LEDs.

There is a LOT more to this Power Factor thing, including various issues that poor power factor will cause. That is all really beyond the scope of this post, but let’s just say that it really shouldn’t be ignored. In fact, poor Power Factor was so important that computer power supplies are required to have Active Power Factor Correction (some CFLs and LED bulbs also have Active PFC, but it depends since it increases the price of the bulb). Industrial plants that have large numbers of high-powered motors and other inductive loads (for example) are required to have Power Factor correction equipment, as well. If they didn’t have the PFC, it would put a huge strain on the grid, and they’d be charged through the nose by the electric company.

So, obviously, Power Factor is rather important and should be kept in mind when planning your lighting. The easiest solution is: don’t overdo it!

Final Thoughts

Now, LED bulbs can be a rather good option. If an incandescent bulb costs $1.50, a CFL might cost $10, and an LED bulb will be $20.

But, you also have to figure that the LED bulb should last the life of 25 normal bulbs, and 25 normal bulbs would cost $37.50.

LED bulbs are also far less hazardous if broken, they run cool, and the light quality really is pretty nice now if you pick a 2700K flavor.

On the other hand, if you don’t get bright enough LED bulbs, you will definitely need to buy a lot more of them to get the same amount of light.

At the end of the day, if you remember nothing else, remember this: LED bulbs should be 2700K. Good luck!

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How to Choose LED Light Bulbs: Efficiency, Power Factor, Color Temperature, and Everything Else
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28 thoughts on “How to Choose LED Light Bulbs: Efficiency, Power Factor, Color Temperature, and Everything Else

  • 4 March 2014 at 02:30

    Really nice explanation.

  • 22 May 2015 at 05:38

    So agree with 2700k being your friend. I’m just about to disconnect 3000k LED lights because they are just not warm enough. Back to halogen until I can find the right LED.

    • 22 May 2015 at 07:21

      Yeah, plus it’s tricky. Some “3000K” LED bulbs are rather bluish compared to other “3000K” ones. I generally find that Philips 2700K LED bulbs are right on the money in terms of warm light.

      • 22 May 2015 at 07:32

        I’ll give the Philips bulbs a go. I’m having sockets installed by an electrician next week. I can then trial plug in LED downlight kits as well, without the need to hard wire. In the meantime I will have plug in halogen MR16 bulbs/transformers. A process of trial and error for me.

  • 14 January 2016 at 17:51

    thanks for the explanation.

    as an older couple we are finding there are physical benefits attributable to brighter light so long as it’s warm white then the duller light of CFL’s. plus LEDs have a much faster warming up period compared to clfs which again is beneficial when you need bright light quickly.

    overall still seems to me that led is the better option

    • 14 January 2016 at 19:03

      Agreed. Most of the latest LED bulbs have a warm-up time of 0. They do dim slowly over time, but in contrast to CFLs, it’s barely noticeable IMO.

  • 25 January 2016 at 19:33

    Sorry, I still don’t understand why we should choose 2700K.
    Are 2700K bulbs more efficient?

    Let me ask this way. Does a Philips 14W, 2700K LED bulb give more light than a Philips 14W, 6500K?

    Or is it something related to human eye that it finds 2700K more bright than 6500K even though the amount of light is same?

    • 25 January 2016 at 21:32

      2700K is the color temperature that is “warm light”. 6500K is very blue/white light, like a fluorescent tube or those fancy HID headlamps you see on (more expensive) cars. 2700K looks more like the incandescent bulbs we all know and love. Actually, 2700K is in reality a reddish light, but our brains tell us it’s “warm white”. That’s a whole other fascinating story, though.

      The amount of light output by a bulb is usually measured in lumens. These numbers are very often measured in different ways, exaggerated, etc. They’re a good general rule, but don’t count on them. In terms of brightness, there are two things to consider:
      1. lumens rating
      2. what kind of light you want

      Sometimes, the 6500K would be a better choice if you want blue/white light. Other times, you want a nice “warm white” light for reading or something, so then go with 2700K. But in terms of the actual measured brightness, a 14W 2700K bulb will usually output the same amount of light as the 14W 6500K.

      After that, it’s a matter of taste, perception, interior decorating, etc. 😉

  • 26 January 2016 at 10:24

    Thanks Scottie. Your reply clarifies my doubt.

    Since we have been using CFL & fluorescent tubes since long in my house so have become habitual towards whiter light and have forgotten the old incandescent bulb light. Therefore, I prefer 6500K. It gives day light type of feeling, which feels good to me. Even in the days when we used to use incandescent bulbs, I liked fluorescent tube light more. So, basically my personal taste is towards whiter light.

    So, as you very well mentioned, it is about personal taste and interior decoration whether one wants to choose 2700K or 6500K.

    Your recommendation for 2700K is for those who are looking for incandescent bulb type of light in LED bulbs but don’t know how to choose.

  • 27 January 2016 at 00:30

    Regarding Power factor:
    I am given a light bulb’s voltage (120 V), power (100 Watts), the current (0.85 Amps), Color temp and lumens by the manufacturer.

    Then I am asked to calculate the power factor. How can I do this?

    Also, when hooked up each light bulb is actually using less power than shown on the manufacturer’s box. ie. only 19 watts for a CFL even though its rated at 23 watts. Why would this be?

    • 27 January 2016 at 12:12

      Power factor is fun! Here’s an intro.

      Basically, any circuit or device that isn’t “purely resistive” will have a power factor less than 1. Resistive devices with a PF=1 would be like an incandescent light bulb, or an electric resistance heater. In the example you gave, if the bulb is NOT a CFL or LED, the power factor is basically 1. That means the current should be 100W / 120V = 0.83333, which is about 0.85A (overrated a tiny bit).

      Normally, PF is given as a another rating by the manufacturer. Plus, the current ratings given are typically for real power, not apparent power. Power Factor is something that the electric company has to worry about, but you don’t in terms of what you pay. IOW, if you’re using an LED bulb with PF = 0.5, and the LED bulb is 5W, than that means your bulb is only consuming 5W of real power – and you will only be billed for that 5W of Real Power. The power company, on the other hand, is generating/sending 10W of Apparent Power. This is due to the impedance wonkiness of the load (in this case your LED bulb), combined with impedance in the power lines, etc.

      If you run a 5W incandescent bulb, it’s purely resistive for practical purposes, so the PF = 1, and the power company only has to generate 5W.

      As for the CFL consuming less power, the W rating is normally for the actual max real power that will be consumed. I would say it’s like a current rating: Just because a device has “1A” written on it doesn’t mean the device will always pull 1A. The CFL bulb may use ~23W when starting, and then 19W in normal operation.

      That’s my 2 cents!

  • 17 April 2016 at 11:38

    “If you need 25% more current, you have 1.5 times the losses.”

    Please correct this to state “…you have 1.5 times the LINE losses.” Power factor does not change the real power consumption of the lamp itself or the real power the utility must generate to power the lamp; it only (possibly) affects the power that is lost in getting the energy from the utility to the lamp. The amount of fuel that a utility uses to power a lamp is based upon the line loss plus the *real* power rating of the lamp, denoted by W, not the *apparent* power rating of the lamp, denoted by VA.

    Further, note that in the hypothetical case that (1) the utility is employing power factor correction devices in their distribution gear and (2) the LED lamp is on a lightly-loaded branch circuit then the line loss could be a negligible percentage of the lamp’s wattage rating.

    • 17 April 2016 at 11:56

      Well, I was attempting to keep things simpler so that more people can understand, not write a technical document! 😉

  • 8 June 2016 at 09:56

    What is the power factor for CFL, LED, Heaters, Halogens, Incandescent Lamps and Sodium Vapour Lamps?

    • 8 June 2016 at 10:42

      Short answer: it depends. Incandescent, halogen, and typical heat lamps are resistive, therefore PF = 1. For all other types, there are ballasts or other electronics that present an inductive or capacitive load, thereby resulting in PF < 1. More or less... But it even depends on WHICH bulb you buy... A 6W LED bulb from the EU may be PF = 0.5, whereas a similar bulb (same brand even) purchased in N. America might be PF = 0.7.

  • 30 June 2016 at 16:36

    Hello sir,
    5W CFL and 9W LED. Which uses more power ?

    • 30 June 2016 at 19:46

      In terms of power that you are billed for by the electric company, the 9W LED consumes more.

  • 24 July 2016 at 16:48

    I did know that electric motors have power factor, but did not know led bulbs have power factor.
    Thank you for your information.
    From Tabriz,Azarbaijan

  • 15 September 2016 at 09:12

    Great article.
    Very clear and simple.
    Thanks so much.

  • 10 March 2017 at 12:23

    Also little known is that within the plastic base of CFLs, there is a PCB (Printed Circuit Board) with about 24 discrete electronic components mounted on it.

    These are typically resistors, capacitors, coils, transformers and semi-conductors, to produce the higher voltage, higher frequency supply required by the Fluorescent Tube.

    Thus there is a much greater disposal problem and wastage compared to simple incandescent lamps, when the CFLs eventually fail.


    I have taken a CFL apart, so know from that practical experience, apart also from having confirmation by circuit diagrams etc.

    To date, I have not managed the same exercise with LED bulbs.

    • 10 March 2017 at 12:41

      The circuitry inside LED bulbs is typically much simpler than in a CFL, but it also varies depending on region and the power factor of the bulb. Higher PF usually means fancier electronics in the base of the bulb.

      It’s still more complicated to recycle an LED bulb as compared to an incandescent… On the other hand, the LED bulbs live much longer! Incandescent bulb life is typically 1000 hours, and LED bulb life varies from 10,000 to 20,000 hours – and sometimes as high as 50,000 hours for fancier models.

      So, theoretically anyway, there will only be 1 LED bulb to recycle for every 10 burned out incandescent bulbs – at least.

  • 15 August 2017 at 10:26

    Great explanation on power factor – many customers just see the specs regarding efficiency in lab tested environments and take it as word, when in reality the diffuser, THD, PF, and other things have major effects on the actual light output.

  • 12 December 2017 at 04:58

    more than 90% of LEDs on the market today have a PF of >.94, leaving the need for such a concern a thing of the past. Becoming more efficient every year due to the drive in competition between manufactures. I would hate for an article like this to deter people from using LEDs.

    • 19 December 2017 at 21:41

      Not in Europe where I live. PF is often 0.5-0.7 for LED bulbs. Just bought some more the other day! The PF requirements differ in various parts of the world.

      That shouldn’t dissuade anyone from buying LED bulbs though, because a traditional bulb using 100W at PF=1 and a LED bulb producing the same light at 13W and PF=0.7 is still a HUGE difference in power consumption. LED still wins on the Eco front, hands down.

  • 29 December 2017 at 04:40

    hi, i hav ordered 2.5 watt eveready led bulbs with .50 power factor,im confused will they consume 5 watt electricity with .50 power factor??

    • 29 December 2017 at 12:39

      Nope. A 2.5W LED bulb will consume 2.5W of electricity – in other words, you’ll pay for 2.5W times X hours of use.

      The PF of 0.5 basically just means that the electric company will (more or less) have to effectively generate 5W of power at their end to run your 2.5W bulb.

      Consumers are usually NOT charged for the apparent power they use (5W), but instead the real power (2.5W).

      • 29 December 2017 at 12:47

        Thank you sir


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