We thought about explaining the technical definition of a lumen & lux, but it’d take too long and we’re about to go for a dive. To keep it simple, let’s take the following defintion of a lumen:
lumen [loo-muh n]noun, plural lumens, lumina
1. the measurable unit of light output. Abreviation: lm
2. a commonly overstated number quoted by light manufacturers
3. a substance highly sought after by cave and wreck divers; and when possessed causes inflated ego and envy among peers.
More lumens equal more light – that much should be obvious. What matters equally is the angle and quality of your beam. Consider the 3 examples below; each light produces 1000 lm, but with differences in optics and reflector technology we’ll have 3 very different lights in practice.
Using Example #1 as a baseline, lets say it channels the 1000 lm very effectively into a solid 30° beam with no spill (ie. halo or outer rings) – we’d have 1x Brightness. We could measure this brightness in Lux, but we’ll leave that for the Internet forum debates. Example #2 again produces 1000 lm and has little or no spill, however the beam is half the size of #1, meaning that the same lumens are focused tighter and we’d end up with something like 2x Brightness.
Example #3 produces 1000 lm with a manufacturer stated beam angle of 5°. In this example we see a significant amount of light spill, meaning that brightness is taken away from the main beam. A relative brightness of 1x or more may be achievable, however the impact of spillage should not be underestimated.
UW Light Dude uses example 2 in either a 6 or 8.25 degree beam angle, depending on model. Our optics are designed for underwater use, are extremely efficient, & don’t have spill.
Beam Angle in Water
Short Version – If your light has a flat lens, your beam will be 33% tighter in water than in air.
Long Version – Refraction, the change in direction of a wave due to a change in its transmission medium (you remember that from school right), causes the light beam to get roughly 33% tighter. The differences between air, lens material (i.e. glass) and water result in a tighter beam. A dome lens as seen on underwater cameras would compensate for the air-water difference and maintain a beam’s native angle underwater.
We rate our light output conservatively so that you can be confident when using our lights. We prefer the measure of lumen over watt as the latter is a measure of power consumption, not light. With today’s increasing efficient LED technology, wattage is legacy practice commonly used to referring to HID and Halogen technology.