Guide Numbers and Watt Seconds - Flash Photography Tutorial #3

In this Part 2 of the Speedlights vs. Monolights battle, we are going to compare Guide Number and Watt Seconds as a way of rating the power of your off camera flash. We are also going to discuss the recycle times of speedlights and monolights.

Monolights are routinely much more powerful than speedlights, because they are larger and able to generate and use more power. Unfortunately, it is VERY difficult to compare them accurately. The reason for that is that Speedlight manufacturers use a method of comparison called guide number which tells you very little about the actual power of your flash and monolight manufacturers use watt seconds for comparison.

Guide number measures the light that is reaching your subject. And watt seconds measures the power that the unit is able to deliver to the flash tube. Two completely different measurements.

But that’s just the beginning of the difficulty… Let’s start with Guide Numbers.

The way to calculate a flash's Guide Number is to multiply the distance x the f/stop. This of course is based on a manual setting at full power and an ISO of 100. Here is an example…. If your flash is 10 feet from your subject and you need an aperture of f/8 to get a properly exposed image – the flash's guide number is 80.

The problem with Guide numbers is that a lot manufacturers measure their guide number with the flash zoomed out to its tightest angle of view – which indeed does measure the most amount of light that the flash can create. But in practice – you probably won’t use your flash nearly as much zoomed in as you will zoomed out and since different strobes zoom to different lens equivalents you wind up comparing apples – to apples – to apples.

Monolight manufacturers don’t make it any easier to compare. Monolights and studio strobes are compared by a metric called watt seconds.

This number is even more unreliable because the measurement of watt seconds is simply how much energy the flash stores and makes available to the capacitor to power the flash tube. It is an unreliable number because different flash tubes have different energy efficiencies as do different reflectors.

In my opinion, the recycle time of a flash is the second most important factor for most people in deciding to go with a Speedlite or monolight.

In this video, I will use a Flashpoint320M Monolight and a LumoPro 180R Speedlight to show you the basic differences between the two types of flash units.

PRODUCTS MENTIONED
Flashpoint 320M 150ws Monolight - http://amzn.to/2bJASeQ
LumoPro 180R Speedlight - http://amzn.to/2bEsxu2
Flashpoint Zoom TTL R2 Flash With Integrated R2 Radio Transceiver http://amzn.to/2bIFwKV

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FTC Disclosure: LumoPro brand equipment was supplied to me by LumoPro. All other equipment is my own. All opinions are my own. Product links are Amazon Affiliate Links which help support the cost of producing these videos.

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Видео Guide Numbers and Watt Seconds - Flash Photography Tutorial #3 канала Joe Edelman