There is a company that already makes LED light bulbs that can be used
as a direct replacment for incandesant bulbs.  Check out the following
page from www.ledtronics.com

Roman Black wrote:

> David W. Gulley wrote:
>
> > > So, 60w bulb = 820 lumens = 11 LEDs!
> > >
> > > Wow, this is almost viable now, since we can get the
> > > white LEDs for under $2 US each.
> > >
> > > Now we just have the problem you so rightly mentioned
> > > re the spherical light output from a bulb, and the
> > > rather poor LED dispersion of 15% or 20% from a beam.
>
> > I do not believe you can just take the 6000mCd output
> > of a directional LED and assume it is spread over the
> > sphere.
> >
> > As I see it,
> >  Assume 6000mCd provided by a LED equally distributed
> >  in a 20degree cone from the LED.
> >  If the surface to which the intensity is measured
> >  is 1m from the LED then the total surface illuminated
> >  is approximately 0.098m(squared).
> >  That is 6 Cd of intensity over an area of 0.098m(squared).
> >  Therefore, this is 61 lm/m(squared) or 61 Lux for the LED
> >
> >  Assuming the 60W bulb provides 820 lumens and
> >  does yield a full spherical coverage, then
> >  820/12.57 = 65 lm/m(squared) or 65 Lux for the bulb
> >
> >  However, the LED is illuminating a much smaller area.
> >  It looks to me that it would take about 135 LEDs to
> >  provide the total lumen output of a 60W bulb!
>
> Yeah, that's what I was hinting at with the LED "beam"
> problem, all their light is very directional. OK, you
> could use a parabolic reflector etc, but that would
> reduce the light intensity a lot.
>
> I tested a 6000mCd white LED just now, it gives a
> very bright 3" spot at 12" distance, and a dim 8"
> diameter glow around that. My "guestimation" would
> be 90% of its light energy is in that 3" spot.
>
> However, when shone upwards at a white ceiling from
> about 24" below, it does give a nice diffuse glow
> circle on the ceiling. Big difference between 12"
> and 24".
>
> I think you could make some nice up-lights, very
> small and unobtrusive on the wall, which throw
> a nice pattern of glowing light on the ceiling
> and may not be lights to read by, but very usable
> for dining rooms or entertainment areas.
>
> Maybe getting a good result is going to be more
> an artistic or decorating challenge than an
> engineering challenge...
> :o)
>
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