Practical Guide to Understanding Flash Power | Slice of Pye, Ep. 21
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In this episode, we’ll give you a definitive guide to understanding flash power and how to determine how much power is right for each scene. (Please note: The photoshoots featured in this video were all filmed prior to COVID-19.)
With so many Profoto flashes available, I wanted to give you a practical guide to understanding their differences and look at how those differences translate in real-world shooting scenarios.
[Related Reading: Radio Flash Systems Made Easy | Slice of Pye, Ep. 19]
Understand How Power Compares Between Different Flash Units
The primary difference between the flashes has to do with flash power. There are other nuances that distinguish the flashes from one another, but the main difference is power. While all of the flashes put out light, they do so in different amounts.
Take the A1, which produces 75 watt-seconds of power; this translates to about 50% more power than a standard flash. The B10, on the other hand, produces 250 watt-seconded of power, which is about five times more flash power than the standard 50 watt-second flash. Other flash units, like the B10 Plus, produce even more flash power (500 watt-seconds and up).
Know Why Flash Power Matters
There are three basic reasons why differences in flash power matter, which we’ll discuss in detail below.
Reason #1 – Why Flash Power Matters: Bright Environments Require More Powerful Lights
Let’s say you’re trying to overpower the sun to create a dramatic image. When you’re setting up your flash to take a test shot in a bright environment, start by following this general rule: “When in the sun, one over one.” This simply means to start by setting your flash at full power. Here’s a breakdown of how each of the Profoto flash units I mentioned will handle in bright environments:
- Profoto A1: With 75 watt-seconds of power, you’ll likely need to shoot at full power with the flash facing directly at your subjects from no more than 5-10 feet away. In addition, I’d recommend zooming the flash head all the way in (which you can do by twisting the top) and using no modifiers. Modifiers reduce light output and you want to get as much light as possible onto your subject(s). If you do use a modifier, such as a grid, you can compensate by moving the flash closer to your subject. Again, this is in a bright, sunny setting. At dusk or indoors, the A1 generally produces plenty of power to provide sufficient light.
- Profoto B10: As I mentioned earlier, the B10 produces roughly 3-4 times more power than the A1. This means that even with a grid, I can shoot from 5-10 feet back. Adding a zoom reflector will allow the flash to get even more light onto your subject(s) in brighter scenes. Given its size and power, the B10 works well in the field as it offers great portability with enough power to overpower the sunlight. Just know that if you add large soft box modifiers like the Profoto OCF Beauty Dish, then you’ll need to move the light source closer to your subject(s), no more than 3-6 feet away. At dusk or indoors, the B10 provides almost too much power, so much so that the modeling light is often enough to adequately light your subject(s). If you’re shooting in-studio with large modifiers and using higher apertures, then the B10 would make sense as a go-to flash.
- Profoto B10 Plus: With 500 watt-seconds of power, we can use a large modifier and still produce plenty of light at 5-10 feet when we set the flash to full power, enough to light an entire group. If you move the flash closer to the subject, you can get dramatic results or lower the power setting to reduce recycle time.
Pro Tip – Inverse of the ISO: If you’re unsure which power setting to use, try using the inverse of the ISO. In other words, if I’m shooting a reception and my ISO is set to 3200, I will start by setting my A1 flash power to 1/32. For Profoto power settings, the fractions of total power break down like this:
- 10 = 1/1 (75 watt-seconds for A1, 250 watt-seconds for B10, 500 watt-seconds for B10 Plus)
- 9 = 1/2
- 8 = 1/4
- 7 = 1/8
- 6 = 1/16
- 5 = 1/32
Reason #2 – Why Flash Power Matters: The Larger the Modifier, the More Flash Power You Need
If you work in the studio and you want more flexibility to use small or large modifiers, as well as higher apertures and lower ISO settings, then you’ll need to use more powerful flash units like the B10 Plus. There are ways to use flashes/strobes with lower power output (which we won’t get into here), but for ease of use, more powerful flashes are the way to go. The B10 Plus is also portable enough to take out in the field.
[Related Reading: In-Studio vs. On-Location Lighting Setups | Slice of Pye, Ep. 2]
Reason #3 – Why Flash Power Matters: Recycle Times Vary Based on Flash Power
The recycle time between flashes can slow dramatically if you’re shooting with the flash set to full power (or close to it). With a more powerful flash, you can use a lower power setting and get a faster recycle time. We’ve already outlined the power output for the A1, B10, and B10 Plus. If each of these flashes were set to 1/32 (or “5” in Profoto’s terms), they would produce a vastly different amount of light.
Therefore, using a more powerful flash like the B10 Plus would allow you to use a much lower power setting to produce as much light as the A1 set to full power. Again, the lower power setting would result in a faster recycling time, which could mean the difference between capturing or missing a moment, especially if your shoot involves capturing action or high speed movement.
You can also find specialized equipment like the Profoto Pro 10 for shooting at extreme speeds, which most photographers may not need.
When it comes to deciding which flash to purchase or which to take on your shoot, think of the different lighting situations. If you’re shooting mostly indoors or during the evening, an A1 will serve you well. For more flexibility with some midday shooting, consider the B10. If you want all out flexibility for outdoor shooting in bright environments with large modifiers and such, then the B10 Plus may be your best choice.
In case you missed our last episode, you can watch them all on the Profoto IGTV channel! We hope you enjoyed this episode of Slice of Pye; please feel free to share or re-watch the IGTV video at any time to reference the material we covered! For more tutorials and lessons on the fundamentals of lighting, check out our Flash Photography Training System!