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.


  1. just came here to say how much I’m loving this course and the questions people are asking which help a lot too.

    I have purchased other courses in the past ( mostly for fashion photography) and 10 years ago attended in person classes at a very reputable studio to learn through classes and assist many photographers too.

    I feel these classes are filling in all the gaps of knowledge I had since then, since I took an 8 year break from photography and I’m finally coming back to do it part time again as it’s been a passion of mine since I was 15 ( I’m 36 now and feel sooo old! )

    all I want to say is thank you! I’m sooo happy with it.

  2. John

    Hi Karl,
    You’ve sold me on moving to flash for product photog(I’m brand new to it) but I’m unsure as to what power to start out with. I have a small home studio in my man-cave and plan to do product, portrait and perhaps some fashion and still-life photography eventually.

    The Godox brand is about my budget window for now – do you have any recommendations on what model and power to start with? Could I get away with some 400w units for a while and upgrade to some higher wattage later?
    Many Thanks for any insight as the flash part is all new to me.

    1. Hi John, if you can I’d go for 600s just to give you half a stop more power if they are in budget. Back in the day though when I was starting out I had a mix of 400s, 600s and 800.

      1. John

        Excellent. Thank you Karl. I’ll shoot for 600’s but also looking for the fastest recycle time I can get with that wattage. 😉

  3. Hi Karl,

    Thank you so much for your thorough and clear explanation. I’m looking to buy strobe lights for a studio space mainly for product photography of about 3x5m meter with low ceilings. I am eying the Godox DP1000 III but I’m afraid they might be to powerful, does that reasoning make sense? Or could do you think I can adjust the power sufficiently?

    Thanks again!


    1. Hi Eva, if you can afford 1000J then great, you can easily reduce the power settings but it is impossible to get more power than is already there, although you can increase ISO by one stop to effectively double the power of your lights.

  4. desavoiecorp@gmail.com

    I didn’t knew at all that when you have a modeling light on and trigger the flash both light are on ; I have always thought that when you triggered the flash the modeling light was shut briefly and only flash was on,
    Did I understood this properly, modeling light is always on during flash bursts?

  5. JarMac94

    Many thanks for these guides. They are enjoyable to watch like a good series, and all the incomprehensible things are effectively developed one by one in your videos. Greetings from Poland

    1. Hi, many manufacturers display there power ranges in different ways. I don’t know the exact light you are talking about but I would guess that 1 is full power and 16 is 1/16th of full power, so that would be a 5 stop range between minimum (16) and full power (1) but as I say I don’t know for sure as they all vary in how they display the range.

      1. dmzbennett@icloud.com

        I have a Godox SK400II Studio Strobe with a 1/16 to 1/1 power range. I am wondering also should I have larger range then this one if I do portrait work or should I just save up the money to get a more professional one like the one in video with that type of display?

        1. Hi, you have 400 Joules available with a 5 stop range so that takes you as low as 13.5 joules so it seems that the range will be good. At full power on 400J if you don’t have enough light then increase your ISO from 100 to 200 and then your light Joules will be equivalent to 800J.

  6. Hello Karl,
    I’d like to ask about power output (joules) between different brands of monolights in different price categories, e.g.. a Broncolor 400w vs a Godox 400w. I assume the quality of the light would be different but how much of a difference would there be in the actual output of light (watts / joules).

    1. Hi, the power output should be exactly the same but in reality they are sometimes a few joules different (but nothing significant). The flash burst on both should be good full spectrum light so you don’t need to worry about that. The difference will be recharge times, speed of the flash duration, consistency of the flash exposure on a series of multiple flashes but shouldn’t be any major differences. The biggest difference in them will be build quality and durability. The brons are built for professionals to throw around from car to location, studio to studio, drop them etc.

  7. Hello Karl,
    On some Canon DSLR (5d series) it is possible to lower your ISO up to 50. However, I am aware that doing so can compromise dynamic range of the image. How do you feel about that? I honestly have never dropped below the 100 mark. In general, would you ever recommend using ISO stops lower than 100 when allowed especially when doing long exposures?

    Thank you for your feedback.

    1. Hi, yes you can drop to 50 and it wouldn’t be the manufacturer’s default ISO but you would hardly notice any difference. Alternatively you can use LEE IRND filters which have ranges of 2 or 3 stops of totally neutral light blocking power but they are expensive filters.

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