Numbers don’t lie. Except when they
do. That’s why you can have so much
fun with statistics. But when you’re
relying on numbers to help you make
a good financial decision, like which
underwater lights to install on a vessel,
the fluid nature of statistical accuracy
can get pretty frustrating.
How bright is bright? Well, that depends . . .
Answering customers’ questions about LED
brightness can be a bit of a crapshoot.
There is currently no standard that all manufacturers use to define output. Some companies cite lumens, but there are different types,
including cold lumens and fixture lumens.
Lenses used in the fixtures, called optics, stir
in still other variables. Courtesy Lumitec
BY ZUZANA PROCHAZKA
ost light manufacturers list some sort of light output rating on their packaging
but it can be a weird mix of lumen nomenclature: raw, estimated, calculated,
cold, and fixture lumens. Comparing apples to apples can be tricky and the
lack of an LED standards governing body allows things to get doubly confusing.
It can make a dealer’s (and boater’s) head spin, so let’s see if we can decipher this dance.
Light brightness is usually measured in lumens, or the total amount of light generated. To
measure lumens, an LED (or the complete light) is placed inside a sealed reflective box known
as an integrating sphere, where light is bounced in all directions and measured at one point.
That is then extrapolated into lumens based on the size of the sphere. (These spheres cost
upwards of $100,000 so not everyone has access to one, but there are laboratories that can test
for a fee.)
Additionally, a lumen isn’t always a lumen. There are calculated lumens, raw lumens and
cold lumens and they’re not created equal. Calculated lumen measurements are sometimes
made like this: An LED emits about 10 lumens per watt, so a 60W bulb will be about 600
lumens. That’s an estimate at best and a lumen lie most likely because it’s based on best case
results. “There are many ways to define the lumen output of a light,” says Gareth Evans,
founder and Chief Technical Officer of Lumishore. “All too often, companies simply quote the
data sheet lumen of the LED device. This data sheet lumen states the maximum possible output
for the bare LED under ideal test conditions, which are impossible to replicate in real life.”
Also, just because a bulb has a higher lumen output doesn’t mean it will appear brighter
when you look directly at it. Looking at the source of light will tell you the lux (the light meas-
ured in one square meter of output area) or amount of light that specifically reaches your eye.
Some LED bulbs focus the light in one direction, and that will make them very bright from one
angle but not another.