LED light bulbs

elstimpo, how long before we have a replacement for incandescent/CFLs, eg 100w equiv, at a reasonable price? Two years, three?

Sounds interesting, elstimpo. They're obviously going to replace CFLs as soon as the price comes down, having more advantages and none of the disadvantages.

I must admit to being curious about the current pricing, if you had the time to enquire. :-)

NB I thought a 100w incandescent was usually around 1200-1300 lumens?

elstimpo wrote: »

I haven't lost any plot. If all you want is a cheap, bright bulb @2750k then why are you considering LED? Why not stick with Halogens as that's exactly that they are? They are cheaper than even cheap LED Spots, they provide a great light, they are the right color. Buy those. I'm not sure why you would be on an LED thread if thats the only criteria you have for a bulb?

OK you haven't lost the plot, but you are being a bit dumb. Of course I'm talking about LEDs, and in your statement "Any company could make......", you should have made clear that you weren't talking about LEDs. After all, this is in an LED thread.

sillygoose wrote: »

Unfortunately LED's do have some of the disadvantages of CFL's as there is a similarity. White LEDS are made by making a powerful LED that emits in its 'natural' chemically defined colour. White is achieved by using this light to excite a fluorescent material along the lines of a phosphor which then emits a white light. So simplistically they are tiny high intensity CFL!

The same issue that fluorescent tubes, CFL versions and CRT video screens suffer remain - they will fade over time as the fluorescent material becomes tired.

This is where intensity, quality and price become very confused - its very difficult for punters to evaluate the fluorescent coating but we can easily see if a bulb is bright and good value. Equally, a LED that seems to exceed in output may seem good value, but not if its burning up it phosphor at an accelerated rate as it will fade quicker!

Being told something is quality isn't enough for me and there isn't enough unbiased historical data on these long living product to feel like forking out a lot of money on them knowing they WILL fade, just not when.

...accelerated testing, useful as it is, its not definitive, ask NASA!

Unfortunately LED's do have some of the disadvantages of CFL's as there is a similarity. White LEDS are made by making a powerful LED that emits in its 'natural' chemically defined colour. White is achieved by using this light to excite a fluorescent material along the lines of a phosphor which then emits a white light. So simplistically they are tiny high intensity CFL!

This is partially true

There are/were two type of LED lamps, those that consisted of LED groups comprising separate Red Green and Blue output LEDs, R+G+B=white, this addition of light is what happens in your TV set to produce all the colours you see (it won’t produce all the colours of the natural spectrum but enough to make it look realistic) The individual RGB phosphor dots convert the electron energy of the CRT into visible light of the respective colours. Split white light with a prism or a rainbow and it breaks up into component colours. Lamps of the type using multi colour LEDs are not used any longer as the performance/quality of light has been far surpassed by the newer type of high intensity LED lamps that do have a central LED, one which cannot produced all the colours or colours in the correct balance to make white light; the light produced is decidedly tinted, generally with a predominately blue/violet hue. A doped phosphor is associated with the LED in order to produce the green and red light which, when all the colours generated combine ensure we end up with white light; altering the phosphor composition will alter/tint the colour of the white light emitted from the lamp. Do you want warm, natural or cool, just alter the amount of red or blue in proportion to the green by altering the composition of the phosphor chemistry.

Simplistically you are partially correct in the assertion regarding fluorescent material.


The same issue that fluorescent tubes, CFL versions and CRT video screens suffer remain - they will fade over time as the fluorescent material becomes tired.

Again basically correct although fade is perhaps not the correct term but conveys the meaning. I’ve got lab CRT units here that are over 15 years old and have had a hard life, continuous running and they still calibrate and work correctly with no signs of “fading”. With regards the fluorescent lamps, compact or otherwise fading or the ability of the phosphor to convert one form of energy into the required visible energy really isn’t the issue with regards fade. The main issue/failure is the metallic electrode/heaters of the tube evaporating and forming a deposited metallic layer on the inside of the tube on top of the phosphor thus reducing the amount of ultraviolet light that the tube generates actually hitting the phosphor. Look at the ends of the tube and you will see that these suffer worst as shown by the pronounced blackening. The output level falls off but not because of phosphor fade which would tend to occur over a far greater period of time. My grandfathers military compass fromWW1 is still fluorescing fine.


This is where intensity, quality and price become very confused - its very difficult for punters to evaluate the fluorescent coating but we can easily see if a bulb is bright and good value. Equally, a LED that seems to exceed in output may seem good value, but not if its burning up it phosphor at an accelerated rate as it will fade quicker!

Being told something is quality isn't enough for me and there isn't enough unbiased historical data on these long living product to feel like forking out a lot of money on them knowing they WILL fade, just not when.

...accelerated testing, useful as it is, its not definitive.

Sure it is difficult for people to evaluate but reputable manufacturers and suppliers are not going to associate themselves with products that are here today and gone tomorrow, they want reliable consistency of performance of the product. The phosphor does not burn up or diminish in performance unless subjected to excessive heat/temperatures which is impossible under normal circumstances, it is far more likely that the LED unit itself will suffer and fail due to the elevated temperatures due to poor design of the associated heatsink device way before any temperatures that would destroy or alter the phosphor. Excessive temperatures will have a far greater effect on the life and output of the LED than any other factor

In all circumstances the performance of the LED will drop off over the years through natural aging processes not limited to LEDs but also other semiconductors. Resins, plastics and glass will also change characteristics over the years and it is likely that these together with LED aging will have a more profound effect on the diminishing of the light output rather than the phosphor fading.

To sum up, phosphors may fade but not to the degree you are indicating and this is more down to a discussion of stability of chemistry at molecular level.

Biggles wrote: »

Sounds interesting, elstimpo. They're obviously going to replace CFLs as soon as the price comes down, having more advantages and none of the disadvantages.

I must admit to being curious about the current pricing, if you had the time to enquire. :-)

NB I thought a 100w incandescent was usually around 1200-1300 lumens?

They are already replacing CFL's. I'm very interested in your intended application for a LED that replaces a 100w GLS. General use around the home a good 7w WW bulb is perfect and often a 4w bulb will do.

It was their claimed equivalent lumens, not mine