LED lamps versus CFLs

(I posted this elsewhere on the internet and thought I would also share it here . . . )

Why Choose LED lamps over CFLs?

LED lamps typically use less power (watts) per unit of light generated (lumens). A good LED lamp can generate twice as many lumens per watt as a CFL (50-100+ versus 40-80).
  - less greenhouse gas emissions from power plants
  - lower electric bills

LED lamps last much longer than CFLs, as much as 10x longer (50,000 hours versus 5,000 hours).
  - fewer spent lamps in the landfill
  - less frequent lamp purchasing/changing, especially important for hard-to-reach lamp locations

LED lamps generate less heat than CFLs.
  - decreased load on Air Conditioning systems
  - reduced danger of burns from touching lamps
  - reduced fire hazards

LED lamps typically are RoHS compliant, meaning that they have no or at most negligible amounts of hazardous substances within the scope of that compliance (lead, cadmium, mercury, ...). CFLs on the other hand all have 1mg-5mg of Mercury (even more in tubular fluorsecent lamps), and no doubt many people are not properly disposing of spent CFLs, resulting in Mercury making its way into the environment, with serious consequences. And if a CFL were to break in your house you might be exposed to Mercury.
  - virtually no risk of environmental contamination
  - no risk of personal exposure to hazardous materials

LED lamps tend not to have unpredictable failure modes. There are stories of CFLs catching fire, emitting smoke and odors, exploding, etc. The ballast circuitry in CFLs can fail in a variety of ways, some not so pleasant for anyone in the same room/house. This is especially the case when market pressure causes the designers to cut corners to save production costs. LED drivers are not nearly as unstable and usually fail by just no longer supplying power to the LEDs themselves.
   - virtually no risk of fire/smoke/odor

LED lamps emit no Infrared or Ultraviolet radiation. CFLs (and tubular fluorescent lamps) generate light by exciting the Mercury vapor inside the lamp with electricity, generating Ultraviolet radiation, which stimulates the phosphor coating on the inner surface of the glass bulb, causing it to re-radiate most of the Ultraviolet radiation as visible light. LED lamps generally create "white" light by using blue LEDs and a phosphor coating which re-radiates some of the blue light as longer wavelength light (yellow range of the spectrum), together appearing as white.
  - no personal exposure to Ultraviolet radiation, which can cause cell damage
  - artwork and other sensitive items are not degraded as a result of exposure to Ultraviolet radiation

LED lamps are not sensitive to frequent power cycling. The lifetime of CFLs (and tubular fluorescent lamps) is reduced by turning them on/off more than a certain number of times per day. The "rated" lifetimes of such lamps is usually based on assumptions that they will be left on, say 3-4 hours, each time they are turned on, rather than having that 3-4 hours be spread out over many on/off cycles. The actual lifetime of a fluorescent lamp will suffer compared to its "rated" lifetime if this "on-time" assumption is not adhered to. This can lead to people thinking they should not turn off their lights as often as might be best for energy conservation purposes, leading to wasted energy.
  - no concern about how often you turn on/off your lights

LED lamps have better control over the direction(s) in which their light is emitted. This is advantageous in applications where you only want the light to go in one general direction (unidirectional) rather than in all directions (omnidirectional). Think of recessed ceiling lighting where any light not directed downward is wasted. LEDs tend to generate light in one direction. By using lenses in the LED lamp, this light can be spread out to achieve various specified beam angles. To do with with incandescent or fluorescent light sources, which emit light in all directions, a reflector must be used (the 'R' part of 'PAR38' for example), and these reflectors are never perfect, causing some light loss in the process. This further increases the efficiency advantage of LED lamps over traditional light sources.
  - less wasted light
 

LED lamps turn on instantly (reaching full brightness immediately).  CFLs tend to have a warm-up period which may range from a few seconds to over a minute.  During this warm-up period they are not as bright as they eventually become.  This can lead to problems ranging from having to wait for light levels to increase to a useful level, wasting your time, to turning the lights on before you really need them, in anticipation of the warm-up period, wasting electricity.
  - no wasted time or electricity
 

LED lamps can be used in colder temperatures than CFLs.  Most CFLs will not turn on or will only emit very low levels of light in the cold (near freezing).  I have not heard of a low-temperature limit for LED lamps although there may be one, but I'm sure it's much lower than that of CFLs.

  - effective in cold temperatures

Why Choose CFLs over LED lamps?

LED lamps are still quite expensive compared to CFLs of similar light output ($50-$100+ versus $5-$10). This initial expense is not as bad though, if you consider both the extended lifetime of LED lamps over CFLs, and their efficiency advantage, allowing them to generate more light from less electricity. I have developed a formula that takes all those factors into account and can give you a cost-per-million-lumen-hours number for any lamp for which you have all the necessary specifications (and the cost of electricity). Recently I ran the numbers on some newly-introduced LED lamps and it is getting closer and closer to being able to justify the use of LED lamps over CFLs purely on the basis of total cost of ownership, without even considering any of the other advantages listed above.

LED lamps are still not as bright and/or small (for their brightness) as you can get CFLs. This means that some applications simply will not have a bright and small enough LED lamp available to fit them (when the lamp must fit in an enclosure).

Very few LED lamps currently available are dimmable. There are dimmable CFLs on the market now, at a somewhat higher price than their non-dimmable versions.

LED lamps are not as commonly available for omnidirectional applications (the classic "light bulb" shape). Due to the unidirectional nature of the light emitted by LEDs, it is a more difficult design challenge to build an LED lamp that can emit light in all directions.

LED lamps do not tend to emit so-called "Full Spectrum" light. Incandescent light by its nature is full spectrum, fluorescent light can be made to approximate full-spectrum light by appropriate use of different phosphors (at increased cost). This approach to achieving full-spectrum light could also be used for LED lamps, but I have yet to see it. People generally cannot see the difference between full-spectrum light of a given Correlated Color Temperature (CCT) and more narrow-spectrum light of that same CCT. Our eyes just average out all the frequencies of light they see and arrive at a single color, whether that color was achieved through many small levels of widely-spread-out frequencies of light (bell-shaped curve) or a couple of large spikes.

Edited by bobkart - Thu, 24 Jul 2008 17:20:29 GMT

That is the tipping point right there, the only think that matters to the majority of consumers, IMO.

As my CFLs burn out, I plan to replace them with LEDs.

Whoops I forgot about another advantage LED lamps have over CFLs: they turn on instantly.

I've edited the earlier post to include this point.

?

only my really old CFLs don't turn on right away, all of the more recent one's I've purchased (within the last 2 years) turn on immediately.

I added some clarification in the first post about LED lamps turning on immediately: yes usually light will come out of a CFL fairly quickly (within one second) but the brightness can be significantly less than what it is once they have warmed up.  Even recently-purchased CFLs (within one year) that I have are like this.

I just remembered another advantage LED lamps have over CFLs, related to the "warm-up" issue: LED lamps can be used (more effectively) in the cold.  Original post edited to include this point.

Great post, and I pretty much agree with everything said.

LEDs are also very robust. We are working with a medical company to use our LED strip lights in their MRI machines since LEDs are not effected by the highly magnetic environment.

I don't quite understand what you mean by full spectrum. Do you mean wavelength? White LEDs are full spectrum in that they cover 450nm - 700nm. We are working with an energy company to use our white LEDs to grow microalgae in a climate controlled tube that is several miles long.

The term "Full Spectrum" applied to a light source refers to the spectral characteristics of the light emitted by that light source.

First, a little background.  Apologies to anyone who already knows this stuff.

A spectrogram is a chart that describes, for each frequency of light within the range of the chart (across the bottom of the chart or X axis), how much light intensity is measured at that frequency (vertically on the chart or Y axis).  If you look at a spectrogram of an incandescent light, it will be a smooth curve, starting out low near the ultraviolet end of the spectrum (shorter wavelength, higher frequency), making a rounded peak in the near infrared, then slowly tapering off a long ways into the far infrared (longer wavelength, lower freqeuncy).  This is the classic shape of a spectrogram for light emitted by a so-called Black Body Radiator, and is pretty much as "Full Spectrum" as you will ever see.  The point being that every frequency of light within the range of frequencies of light emitted is present, with more in the middle and less near the edges.

en.wikipedia.org/wiki/Black_body

Electrically exciting mercury vapor in a sealed tube (fluorescence) will emit ultraviolet radiation (shorter wavelength and higher frequency of light than is visible to the human eye).

en.wikipedia.org/wiki/Fluorescent

Phosphors are chemicals that are excited by radiation/light and after they absorb that energy they then release the energy, again as radiation/light (photons), but at a frequency that is not related to the frequency of the light that they absorbed, but rather to the specific chemical makeup of the particular kind of phosphor involved.

en.wikipedia.org/wiki/Phosphor

Fluorescent lamps use a combination of fluorescence and phosphors to emit light in the visible spectrum, but the spectral distribution of that light may or may not be considered Full Spectrum.  Whether that is the case will depend on how much effort went into formulating a mixture of several different kinds of phosphor, such that the range of frequencies of each of the kinds of phosphors combine to give an approximation of a Full Spectrum spectral distribution.  Some fluroescent lamps claim to emit Full Spectrum light while others do not, and it is the complexity of the phosphor mixture that makes the difference.

en.wikipedia.org/wiki/Fluorescent_lamp#Phosphor

Still, the spectrogram of a fluorescent lamp will have spikes and dips as opposed to the smooth curve of a true Full Spectrum light source such as an incandescent lamp or the sun:

en.wikipedia.org/wiki/Color_temperature#Spectral_power_distribution

LED emitters typically emit very narrow-band spectrums of light centered around their color (red, blue, green, etc.).  Even if you created a white LED lamp using red, green, and blue LEDs, you would not get Full Spectrum light although the light would appear white:

en.wikipedia.org/wiki/LED#RGB_Systems

But few LED lamp designers use this approach, partly because of the extra cost involved, and also due to the "rainbow fringe" problem: because the red/green/blue light is not coming from exactly the same point, the edges of the shadows of objects illuminated are not crisp but instead have some combinations of red/green/blue appearing in the transition from light to shadow.  Instead they use phosphors just as in fluorescent lamps:

en.wikipedia.org/wiki/LED#Phosphor_based_LEDs

and this solution typically yields the same kind of "spikey" spectrogram as with flourescent lamps, even more so due to the very narrow-spectrum nature of LED light emissions.  Look at the spectrogram on that page and you can see how unlike a classic Full Spectrum spectral distribution it is; there are spikes and valleys indicating "too much" of some light freqeuncies and "not enough" of others.  It still looks white but hardly has the nice even spectral distribution associated with incandescent sources or even fluorescent sources where they have taken the trouble to create a wide/full spectrum of light by using a complex mixture of phosphors.  As I mention in the first post, LED lamps could utilize the same approach of complex phosphor mixtures to achieve a more Full Spectrum of light, but I have only seen that done once in over a year of researching LED lamps.  But perhaps it will catch on.

I found more discussion of these issues here:

www.gnurple.net/2008/04/27/cfl-vs-incandescent-the-bulb-shoot-out-continues/