It still sticks out like a sore thumb to anyone on a technical bent.
The use of watts to define the luminosity/brightness of a (car
headlight) bulb is fundamentally flawed and I know everyone does it!
eg. The luminosity/brightness of a 30w HID is not the same as 30W
fluorescent or 30w tungsten or 30w LED or a 30w sodium discharge, etc.
But hey it's not that important.
Brightness, being a subjective perception, if you see what I mean,
colour temperature etc., taken into account.
'and I will make it a felony to drink small beer.'
That is part of the point that writer is making; the marketing hype is
pseudo-science, not the real thing at all. The "... watts of light" thing
isn't his choice of words. But Watts are a unit of "power", ie one Joule
(of energy) per second (of time). Light is energy, so it isn't
necessarily wrong to use Watts to measure light - but Lumens are a more
useful unit for measuring the output of lamps, and Watts for measuring the
power used to drive the lamp.
It's that latter usage (power consumption rather than light-energy
produced) that is usually meant by the marketing types, to relate things
to customers' familiarity with household incandescent bulbs which are
traditionally classified by power consumption. You can find similar
contortions on the packaging of 'high efficiency' (ie fluorescent) lamps.
Look at the phrasing here for what is being referred to :
"....plus 50 per cent category, which refers to the amount of light
produced 75 metres ahead of the car compared with a standard bulb"
I admit that they don't say how they measured or in what units, but I
suspect that this addresses the question of whether the gains are real
or snake-oil/marketing hype.
Halfords and Auto Express don't seem to be talking about any unit of
measurement in particular, and don't mention any. They just claim a vague
comparison with an undefined "standard bulb".
I do take issue with Auto Express's statement "[...] But, for most of us,
the best way of improving visibility in the dark is to fit brighter
headlamp bulbs." Brighter headlamps may be of use to people anxious to
drive as fast as possible on empty unlit roads (or off-road; rallying and
racing, in other words) but in the real world, brighter headlamps just add
to the useless glare and dazzle that all road users have to cope with.
I would hazard a guess that the magazine just held a photographer's light
meter in the middle of the 'beam' to compare 'brightness'. That's a pretty
meaningless comparison. What needs to be compared is how easily the driver
can interpret what is illuminated by his lights - and what isn't directly
'in the beam', as well as what is. Too bright a beam actually makes that
more difficult, unless the vehicle is fitted with several lamps to 'flood'
the area with a spread of more or less even light - as can be seen on cars
taking part in night rallies. At the same time, the effect of the lamps on
what other road users can usefully see needs to be taken into account.
Photography is not a good guide to what the human eye and brain can
perceive; cameras do not work the same way as eyes and brains.
My sympathy is with the French legislators who wanted everyone to have
their headlamps tinted yellow to reduce glare and dazzle. Too much light,
particularly in the wrong place, is at least as bad as too little.
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