This subject is near and dear to me; I was an early CFL
and LED adopter.
Incandescents have long been derided as room heaters with a minor by-product of light. They offer a good balanced spectrum, and the heat is useful in some applications like chick brooders. In a recent flame war about government taking away our freedom and liberty banning 100 watt bulbs versus damn hippie green Al Gore CFL/LED "conspirators", one of the vehement anti-LEDers admitted a good
personal reason for using an incandescent- he lives on a farm and his butt would literally freeze to the outhouse seat in winter without an incandescent burning.
CFLs were a better step up energy-wise, though the mercury is troubling. From the early circuline and compact U-tubes that tended to let the smoke out of their transistors before the light output had time to fade with age, to the well evolved compact cold cathode units that came out in later years, they really became quite good and reliable. Much of their inefficiency and aging comes from producing mostly UV light with the tube, which must be downconverted to visible light by phosphors, stacking two inefficient processes.
LEDs are more efficient by directly producing visible photons. The "white" LEDs use blue emitters, some of which is converted to other wavelengths by phosphors; mostly yellow. Better LEDs apparently have a mix of phosphors for a very wideband emission surpassing the peak-y output of CFLs. Cheaper ones are mostly blue plus yellow, giving very crummy color rendering especially with reds. I found it hard to correctly cook meat on my RV stove with ~2006 technology "white" LEDS until I added some red ones to the fixture. For dry camping, LEDs can light the whole trailer with power to spare for indulgences like blue undercarriage lighting, for less than two traditional 12v 21w fixture bulbs. Now if we could work on the noisy, watt eating furnace blower!
Cool white LEDs are quite blueish and I prefer them for work lights. Warm white emphasizes yellow, too much so for my taste except for decorative applications. Some manufacturers now have a "natural white" which is a pleasing medium.
Home Depot recently had a promotion where 40w equivalent Cree fixtures were $5-something, down from $19+; needless to say, I snatched up a lot of them before they went back up a few dollars. These offer a superior near omnidirectional pattern because the emitters are mounted on a tube pointing radially within the globe and are about the best drop-in replacement for incandescents I've seen. LEDs are very directional, and most bulbs have them aiming one direction from a flat board, which works for some applications but tends to give traditional lamps an unpleasant lit appearance. Nowadays, there are more and more specialized spot, omni, and 90 degree emitting bulbs out there.
I've tried many many types of chinese LED bulbs from ebay. Quality is all over the map. I've never seen a simple inline resistor in a line-supplied LED fixture. The cheapest have a few diodes, capacitors, and resistors on a circuit board. Now more are stepping up to a complex circuit including an IC or two, usually rated for 85-265 volts- pretty versatile.
Dimmable LEDs are a special design and more expensive, but not by much. Cheaper ones are more prone to strobing, buzzing, or EMI, but these seem to be getting ironed out over time even at the low end.
Many of the chinese sellers list them by CFL equivalent wattage which is much higher than consumed power for comparison purposes, and the brightness equivalence is usually dubious anyhow. Caveat emptor.
SMD or surface mount device type are typed by MM dimensions; 5050 = 5.0 X 5.0 mm. These are good for lower wattage bulbs for night or fill/effect/mood lights, but there are better alternatives to higher wattage needs than the now ridiculous, 100+ emitter corn or disc lights.
COB or Chip On Board is the latest and greatest- a lot of emitters on a compact, easy to heatsink plate. These make great spot fixtures, and well designed 3/4 globe bulbs give good omnidirectional output. I saw a bulb that had 5 small COBs mounted at slight angles for an even better omni pattern, but have yet to buy one. Wattages are reaching 200 and these are screaming bright; even a 10 or 20 watt chip is too bright to stare directly at.
High power color LEDs are seeing interesting applications now too, from architectural color lighting including RGB 16 million color rendering to LED stage lighting without miles of thick snake cables; "actinic blue" for aquariums with blue and cool white emitters on one chip for a great undersea effect, to red + blue or even multi-band on one chip plant growth lights that hit the chlorophyll absorbtion spectra so directly that the leaves are said to look black under them.
No, I'm not selling LEDs, just an avid user!
