By on 2011-10-25

Watt Seconds need not be confusing.

Who’s on First? Watts on Second?

There is quite a use of the term “watt second” in our industry. It has come to represent the power of a strobe. However, this is not necessarily the most accurate method to compare power for strobe units. The current definition of watt second is a unit of stored energy.

Why do watt seconds matter & why understand them?

It is extremely important to understand that watt seconds are not the most important part. It’s almost like shopping for a new TV. Just as screen size will not determine the quality of the TV, the amount of watt seconds should not be the only determining factor.

What should I look for?

When shopping for a strobe you should look at some of the following that sometimes may be overlooked:

  • The flash tube’s ability to convert energy from electricity to light
  • The reflector and its ability to control spill
  • The strobe’s consistency and its color temperature over 100 shots in a row

How does Westcott gage ‘watt seconds’?

Westcott has developed a method to compare true output using real world methods. Powering your light at full power in a 24×32 soft box at a given distance you can accurately compare the true light output.

For example, let’s look at two of the Westcott lights – the Spiderlite TD6 and the Strobelite Plus.

So, which is more powerful? Let’s look at the Actual Meter Reading (AMRs).

  • Spiderlite TD6 – 1200 eq-watts: ISO 400, 1/60th Shutter Speed,  f8
  • Strobelite Plus – 400 eq-watts: ISO 200, 1/125th Shutter speed, f22

With this method you can see the difference in power immediately.

Shout-out to the Strobelite

Back in August, a dealer over in the United Kingdom, did a great review on our product and posted it on their blog. We were excited to see such a great review! And added to all the great critique they had in their blog, they mentioned the one thing that is probably the most important – light consistency.

The power output was very consistent as I took a series of readings throughout the day.

Our Strobelite series is incredibly efficient at transferring the energy for the wall into usable light. This efficiency creates a strobe that can output more light with less energy. Which is why the use of watt seconds as a standard to compare strobes is not very accurate.

What do the Top Pro Photographers think?

Quality of both the light as well as the build is always extremely important, but don’t take it from us, take it from Westcott Top Pro, Courtney Dailey.

The Strobelite Plus is my workhorse. These puppies are durable and accurate. I like the feel of them and their build is like a tank. As a traveling photographer they always have a happy landing at LAX, intact!
— Courtney Dailey

Related Topics

Categories: Photography Tips;
Format: Articles;
Brands: Westcott Pro;
Topics: General Photography Tips;
Gear: Speedlite Flash and Studio Strobe

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1 Comment

  • TIP: This is a more useful comparison :

    * Spiderlite TD6 – 1200 eq-Watts : ISO 200, 1/125th Shutter Speed, f 4
    * Strobelite Plus – 400 eq-Watt Sec: ISO 200, 1/125th Shutter speed, f 22


    * Spiderlite TD6 – 1200 eq-watts : ISO 200, 1/125th Shutter Speed, f 5.6
    * Strobelite Plus – 400 eq-watt sec: ISO 200, 1/125th Shutter speed, f 22

    These examples demonstrates an important difference between continuous and flash power, and why Watts and Watt Seconds must not be confused.

    Continuous light sources such as the TD6 are measured in Watts. Changing the shutter speed changes the required aperture.

    Flash light sources power such as the Strobelites is measured in Watt Seconds. Changing the shutter speed does not change the required aperture provided you stay below the cameras sync speed. Flash is very powerful and all the power is put out in a very short time – quicker than most cameras can open and close the shutter.