Understanding Flash Power

Confused by flash? Empower yourself with full creative control by learning how to control your lights.

Before you can achieve top-quality results with your studio lighting, you need to understand power. This class breaks it down into simple, easy-to-understand steps.

Each type of studio light has different power capabilities. To harness those capabilities and give yourself full creative control, you need to make flash power work for you.

This photography class covers all you need to know about flash power, including the relationship between f-stops and studio light power, why it’s important (but not necessarily crucial) to have a large range of power, and the factors that influence power.

In this class:

  • Joules and what they mean
  • The relationship between f-stops and studio light power
  • Factors that influence power
  • Achieving the correct exposure
  • Power ranges and how to overcome a limited power range
  • Power output comparison between studio light power and speedlight power

Questions? Please post them in the comments section below.

Comments

  1. Hi Karl,

    Never afraid to ask what’s possibly a stupid question – I know you said shutter speed doesn’t matter with flash lighting but would you not be able to affect a reduction in f stop when the flash head is at its minimum by having a faster shutter speed?

  2. Hi Karl, excellent tutorial! So high speed sync allows you to use variations in shutter speed to balance the flash with ambient light?

    1. Exactly right again Clive. You’ll see this most commonly applied in my fashion shoots when I’m on location, as in ‘Fashionscape’ in the ‘Fashion’ section.

  3. Great info! In a typical studio what is the starting distance of the main light usually? Is it 4, 6, 8 or 10 feet? And lastly if you have to move the main light back to reduce power is the floor marked at all if so in what increments?

    Thanks

    1. Hi Edmond, I’m not going to answer that question until you have watch the rest of this course or at least up until chapter 25. If you feel you need to ask me again at that point then we’ll discuss it as you should learn some fundamental information along the way that I need to make sure you absorb so you can master lighting.

  4. Hi Karl
    Can you please clarify – if your flashgun is 2,5 stops slower then your Siros light does that mean that flashgun is approximately 150 joules?
    Also I tried to calculate what minimum power of light I should have for product photography and for example if I need aperture 11 then light power should be 50 joules and that fits even to flashgun. But what do you think the minimum power of light source(I mean flash type) that can be used for product photography?

  5. Hi Karl,
    Did I hear correctly if I heard you say you where shooting at 1/60 of a second? Or was it 1/160 of a second? I guess you will cover the lamps sync speed later and how to relay to the sync speed.

    Regards

    1. Hi Tom, yes that was 1/160th of a second just to make sure I cut out any ambient daylight from the shot but I will be covering more in this and sync speeds in later chapters.

      1. Hi Karl,

        there is one thing which is not quite clear to me about apertures. On your sheet you show aperture sizes in order where there have 1 f stop more or less light coming trough. Between aperture f8 and f11 is one stop of light difference. But what about f9 and f10? How to calculate the light difference in between? Same for aperture sizes between F22 and F11 (F20, F18 etc.) Of course I could adjust my light by just shooting and checking, but I would like to know how much impact the “in between” apertures have and if there is a different math to consider. Thank you

          1. Thank you Karl, I guess saying 1 stop less or more light was wrong :), but you got my question anyway. I’ve watched the classes you mentioned before, but did not catch the part about the “inbetween apertures ” as 1/3 as of an fstop change. Now it’s totally clear, thank you.

          2. Hi, Remziye. Glad you’ve got it worked out but just to clarify saying one stop less or one stop more is completely accurate when referring to a specific amount of change in exposure – that amount being either half or double each time is known as ‘one stop’ you can of course change flash power in one stop values (or 1/10th of an fstop) but in aperture terms one stop jumps refer to the scale such as f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45

    1. Hi Kamel, you can only increase the shutter speed to the maximum speed that it will still synchronise with flash but as explained and you will see in a later chapter, this has little effect on the exposure of the flash it only reduces the ambient exposure. Please see the later chapter.

  7. Excellent tutorial. I’m glad you showed the relation to speed lights also. I work with speed lights, so it helps understanding the difference in power between the two types and the limits they can achieve. I can appreciate why you would buy strobe flashes.

    1. Hi Geoff, thank you. The main reason is the use of modifiers and then of course the extra power to get through the modifiers (as you lose light) and also convenience of consistency, ease of use and the batteries not draining.

  11. Thank you Karl , Excellent education . You make it simple through your poised & clear teaching and bring these constellations of tips and tricks which are so practical like opening a pandora box. Will surely spread the word. Sometimes while you are teaching i pause the video and almost ready to ask you a question : ) then it flashes ! its a video . Thanx once again for bring this education so live and spreading u wisdom of experiences .

  12. I’ve just finished the second video. This is exactly what I’ve been searching for. I love your style of teaching!!

  13. Hi Karl,

    Does the modeling light really affect the shot ? I was under the impression that due to the power of the flash and the sync speed, the modeling light has no effect. Plus, I felt that the flash unit temporarily switch it off during the firing.

    1. Hi Anan, if you have bright modelling lamps like 650w and shooting at apertures such as f8 or larger then yes the modelling lamp can definitely become a problem. It is a common mistake that photographers make in the studio by not accounting for the modelling lamps. Which can then cause unwanted colour casts or add blur to an image when you would have expected a frozen sharp shot from the flash.

    1. Hi Trond, you certainly could reduce the amount of light captured by one stop if reducing the ISO was an option. On my Hasselblad definitely yes as 50 is the default ISO but on the Canon the default is 100ISO and dropping to 50 actually causes a slightly lower quality image than at 100. Each cameras sensor has a ‘sweet spot’ ISO, I believe on Nikon it is 200ISO.

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