If
you have a basic physics grounding and/or have researched buying a
bike light lately you are probably a mite confused right now. All
the manufacturers seem to rate their lights with different methods
whether that is watts, candela, lumen or lux and it just muddies the
water for the punter on the street.
To
clarify my stance early on, I work for Amba-Marketing, the UK
distributor for Busch & Muller and Supernova. I bought my first
B&M light in the late 1990s (Thank you SJS Cycles) nearly a
decade before I left the military and entered the bike world . Over
the last 20 years I have used lights from B&M, Smart, Axa, BLT
and Cateye for both battery and dynamo. I was given a B&M Ixon
IQ by Amba the first winter they were on the market as a sales
bonus/trial. I will not hide my respect of B&M's lights they
have served me well on tours, club rides and some mostly unlit rural
commutes. From my first halogen fuelled Oval to my current LED Oval+
with my trusty Seculite or D-Toplight depending on the bike, I'm now
a kid in a sweetshop genuinely unsure what to replace the Oval with.
You
only have to visit a cycling forum to discover a variety of differing
opinions on what light to have. The trouble is once you get past,
“It says 300 million lumens and only cost me a tenner” what do
you actually know? So in the third of a number of blogs on
terminology todays subject is;
Lux
This
is where the two previous articles meet up and all nearly becomes
sweetness and light. Lux is the SI unit of
illuminance and
luminous emmitance, measuring luminous flux per unit area.
Illuminance is the total luminous flux incedent on a surface per unit
area, it is a measure of how much light illuminates the surface based
on an average sensitivity of human perception of brightness. We all
see light differently depending on our eyes so science uses a known
average, So what we have is lumens = Quantity and Lux = intensity on
a surface.
It
is arguable that Lux is a more useful unit for the comparison of bike
lights which is our initial quandary. However, alone it is also
fairly useless unless you have the distance the light is measured
from the source. Also it says nothing about field, consistency or
colour of the light. So we may have 100 lumens at a point x metres
from the lamp but what is the reading 5cm in any direction? We just
dont know. So a field map of the light intensity helps us but only
if all the manufacturers produced their output in a standard format
(Flying Pig1, this is air traffic, remain on pan awaiting clearance
to taxi) Power isn't everything, because how you feed all this light
through a lens also varies how much light goes where. My old IxonIQ
has a third more lumens than the new IQ but the field pattern is much
improved on the new model so in this case more lumens doesn't mean
more light.
In
conclusion while our three main measures used in bicycle lighting are
all linked non of them tell us precisely what we want to know. If
however a few key distances and comparable lumoinosity maps were
included in the promotional bumph we might have half a chance of
accurately comparing light a to light b. As it stands the closest we
can get is the reviews in the paper press hoping the photog switched
off autocorrect so they're all on the same aperture and shutter
speed. Will the bike light industry buy into this? Some have but as
there are so many tuppeny ha'penny mass manufacturers out there
putting quantity over quality it's doubtful. So we're still going to
be stuck with the guy on the club forum banging on about the 3K Lux
light he got mail order from Ulan Bator. You know the one he'll have
two on his handlebars and one on his helmet secured with duct tape
and melting the retina's of any poor soul coming towards him so they
cant see where they are going, he's fine though.
