Shedding light on new
technology
Since the early days of police cycling,
IPMBA has been recommending that any public safety cyclist operating at night
be equipped with a ten-watt minimum headlamp. This was to help ensure that
departments did not skimp on lights, leaving their personnel vulnerable to
night-time road hazards. Over the course of the years, the "10-watt minimum"
became established as the IPMBA standard. This worked fine for as long as
bike lights utilized bulb technology. Then along came the LED (light emitting
diode), and things changed. However, the way we think about brightness did
not - and it should.
What do you do when the light in a room is not bright enough for reading?
Chances are, you replace it with a bulb of a higher wattage, which makes
the room brighter. Higher watts = brighter light, right? Wrong. As defined
by the IES Lighting Handbook, 5th Edition, Light Research Center
(www.lightresource.com), a watt is a unit of measuring electrical power.
It defines the rate of energy consumption by an electrical device when it
is in operation. Light is measured not in watts, but in lumens. A lumen is
defined as a unit of light flow that is the measure of the total light output.
Lumens are basically the amount of light that falls on an area at a certain
distance from the source.
The light produced by both halogen bulbs and LEDs is measured in lumens.
The amount of energy consumption used by both types of lights is measured
in watts. In comparing the two, it is important to examine the amount of
light produced and the amount of energy it takes to produce that light. The
IPMBA standard is primarily concerned with the output of light, or lumens;
however, the wattage necessary to produce the minimum light output is also
important, as it affects the battery life and subsequently the length of
time one can patrol in the dark.
A test was conducted comparing a 10-watt, dual halogen light and a one-watt
LED. The halogen light put out 42 lumens of light measured at 10 feet and
nine lumens of light measured at 20 feet. The LED put out 80 lumens of light
at 10 feet and 21 lumens at 20 feet. The LED, therefore, produced nearly
twice as much light while using nine times less power.
The development of LED technology for use in bicycle headlamps has necessitated
a change in the way in which the lighting standard is defined. The bicycle
of any public safety cyclist operating at night, therefore, should be equipped
with a headlamp (that is, a light whose purpose is to light the rider's way)
that produces at least 42 lumens measured at a distance of 10 feet from the
light, and nine lumens when measured 20 feet from the light.
There are many factors that go into selecting a light - weight, configuration,
color, battery life, price - but when it comes to brightness, think lumens,
not watts.
Thanks to Alerte Systems, International
(www.alertesystems.com),
for conducting the research and providing the facts for this article. Future
specifications released by IPMBA will measure brightness in lumens rather
than watts.
© 2005 IPMBA. This article appeared in the Summer 2005 issue of IPMBA
News. |
