In article ,
Rob G writes:
I went off to look at bulb outputs, and found this website
http://www.lrc.rpi.edu/programs/nlpi...erformance.asp
The measurements are for 50w bulbs so it would seem that the 240
lumens claimed is pretty good and hence meets Vortex's subjective
measurement.
One of the interesting things is that halogen MR16 have been measured
at the centre of the beam which is much narrower than the 120 degrees
from the LED ones. If indeed these LED bulbs are subjectively good
with this much wider beam then it does look as if things are going in
the right direction.

Note that lumens is the total light output from a lamp summed
in all directions. (In theory, it's measured by using what's
called an "Integrating Sphere", which sums the light output
in all directions to calculate the total lumen output.)
So the lumen output is unaffected by things like beam angle.
Intensity of a beam is candella (which is effectively lumens
per solid angle, i.e. within a cone) and intensity of a lit
surface is lux (which is effectively lumens per area).

Many of the LED lights around have quite high intensity beams,
but an extremely small solid angle, so the total lumen output
is tiny. That's why they look bright when you stare back up
the beam, but don't manage to light up anything much bigger
than an ant crawling directly under them on the floor, never
mind a whole room.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]