Back to the LED part. Firstly, I dunno about them ever replacing a light bulb. Maybe, but somehow I doubt it will be the LED that we presently know of.
The reason why an LED can look bright, but not actually be bright is complex.
The "water clear" generation we have today are different to the older generation of coloured LED package. The water
clear packages use differeing elements to gain the colour. These "seem" to be brighter because of several reasons. Firstly, the package being clear, allows more light to pass through it. Additional to that, but a little more complex, in an old coloured package, the light produced was white. White light is broad spectrum. Thus the coloured package filtered a lot of the unwanted light, allowing only the colour of the package light to pass through it. This results in less light energy radiating away. The clear designs produce only a light of the wave length it was designed for. So thus, all the electrical
energy producing the light, goes into that one specific clour. Hence the water
clear packages seem to be brighter than the older coloured ones. OK.
Now why I commented above about the lightbulb part is for the following. All LED's, no matter what physical size, take close to ruffly the same amount of power to produce the light they do. The differences of power consumption
between them are due to the materials used to produce the light spectrum. Some require more current
, some require more voltage, blah blah, but all in all, about 100mW @ 2V is the middle ground for most. Some will take very little and some will take upto 130mW @ 4V. The most I know of, is a red one that can max at 135mW at 5V and produce 20,000mcd. But here is the next tricky part.
The view angle. So all LED's are ruffly the same power consumption
, and ruffly the same light output. So how do you make them brighter? you take all the light energy and focus it into a beam. The tighter the pattern, the brighter it seems to us. It's not really any brighter, just more photons get to arrive at our eyes, instead of being scattered into space. The really bright LED's are usually the tightest patterns. About 15 degrees is the tightest and figures of 10,000 mcd and more, are usually 15 to 20 degree tight patterns. So this means you have to have a lot of LED's around in a circle to get a good 360 pattern.
You will also notice that the good expensive light units, like Hella and aquasignal, have a focused lens that takes a lot of the light that would have radiated vertically and focus into a horizontal pattern, thus making the light travel further for the given candle power of the bulb.
And finally, although not really as importantly,
The colour, and what we can register with our eyes. Certain colours are harder to see than others. Dark blue and dark red being the extreme ends of the light spectrum, make it hard to distinguish. So you need more light intensity for us to "see" it. Blue is very difficult for us to focus on because of the very short wavelength and Red because of the very long wave length. Beyound those wavelengths, the light energy enters into ultraviolet and respectively, infra red, niether of which we can detect with our eyesight.
And to end, it is also interesting, that even white light can be made up with certain other wave lengths being a dominant background. This is often the case in gas discharge types like flourescent light. Those long tubes can come in all sorts of colour backgrounds. There is one that is a hot white. It has a lot of blue spectrum in the white. It seems very bright and very white, yet it is very hard to see anything when trying to read for instance. A bad light type to have in an office. So often in offices, you mix the tubes with a cool white as well. That has a lot of red spectrum in it and softens the harsh tube. Then you can add a yellow spectrum and that makes a better reading light and so on.
I have tried to keep this easy to understand, not so much techincally accurate. So please don't anyone get nit picky with the above. I am sure I have bored many already.