LUX, LUMENS & GUIDE #'s

[bradsab]

Can anyone give me a crash course on the difference between LUX, Lumens & Guide # (for strobes)? I have a (very) vague idea of what they are, but how do they relate to each other?

 

[pete340]

Can anyone give me a crash course on the difference between LUX, Lumens & Guide # (for strobes)? I have a (very) vague idea of what they are, but how do they relate to each other?

Lumens measure the total amount of light. The brighter the light, the higher the lumens. Lux measures the number of lumens per square meter. The farther the light source is from the target, the lower the lux, because the light spreads as it leaves the light source. The guide number relates distance to f-stop. Divide the guide number by the distance from the camera to the subject to get the f-stop that you should use. Or go the other way around: for a given f-stop, divide the guide number by the f-stop to determine how far away you should be.

When you see these numbers as ratings for a strobe, higher lumens means brighter light. Higher lux at the same distance means brighter light or tighter beam. Lower guide number means higher lux.

 

[bradsab]

Thanks, Pete, that clears it up for me. Adding to my confusion is the published coverage area for strobes. Some list a lower guide number, say 10 or 12, but the area would appear to be smaller. The problem is they don't always use the same terms. Some use degrees while others use lens length, i.e. 80* vs 28mm. Is there some kind of formula to convert one to the other?

 

[bobf]

If your goal is to compare features, you can find most every underwater strobe listed in the StrobeFinder:

Underwater Strobe Comparison Guide - Digital Diver Network

Terms like Lux and Lumens will not be listed among the categories, but Guide Numbers, Watt seconds, and Coverage (aka Angle of Coverage or Beam Angle) are among the 25+ categories listing manufacturers specifications.

All Guide Numbers listed in the StrobeFinder are noted in Meters, sensitivity set to ISO 100.

All information found in the database has either been supplied or confirmed by the manufacturer of each strobe.

You may choose to view more than one strobe at a time to make comparisons a bit easier.

hth,
b

 

[bradsab]

Thanks for the link.

 

[bradsab]

If your goal is to compare features, you can find most every underwater strobe listed in the StrobeFinder:

Underwater Strobe Comparison Guide - Digital Diver Network

This is a great resource. Is there any such comparison of dive lights?