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, yes if necessary but it’s easier to adjust the power as you don’t affect the size of the light to the subject which would have implications on how the light looked, which is covered in other classes.

  2. Thanks for this video Karl.
    I have another question relating to my earlier question about purchasing the Godox AD600 pro heads for product photography and all commercial work moving forward.
    I am currently test shooting with a 600Watt monoblock studio light left over from my real estate photography days. The problem I have run into is that I don’t have all the power that I want to play with. I have the camera set at 1/160 sec, ISO 100, f16, and that is just fast enough to cut out 90% of the ambient light in the room. I then have the strobe set to full 1/1 power with just the basic small reflector as seen in this video. The strobe is 8 feet away from the subject and pointing directly at it.
    I am getting an exposure thats just exposed enough or maybe slightly underexposed. Considering in the future I want to shoot with the light 10-12 feet away in order to create that crisp shadow edges look I can only assume that I need stronger lights. Is my assumption correct?
    Would need to purchase 800 or even 1200 heads instead of the Godox 600 heads
    I’m happy to drop a link to the test images if you like.
    Thanks Karl.

    1. Hi, maybe you need to open the aperture more and see if you can increase your sync speed to 1/200th or 1/250th if possible. Otherwise remember that an 800 Light is only about 1/3 of an fstop brighter. A 1200 light is one stop brighter than a 600.

  3. Hi Karl,If I use hss does it affect the lifespan of the flash tube?
    Do you perhaps know the company Parabolic?

    1. Hi Heinz,

      1. Possibly a small amount if you used it for every shot as you will be using the flash tube on a more powerful output but I think the effect would be very small, it would be similar to just using the flash tube normally but on the upper power levels.
      2. No. I’ve heard of one called Parabolix. And of course I use the Para (Parabolic) reflectors from broncolor.

  4. HenrikSorensen

    Hi Karl,
    Once again a solid and good video. I now get it – before I just used it …..
    However, I don’t understand why my Elinchrom lamps (250’s) ranges are from 1.3 to 5.3 – why not simply 1 – 10 …. that would make things a lot easier …. like it is on your lamps or e.g. on my profoto A1x … 🙂

    1. Hi, choose Manual (TTL is a waste of time on studio lighting) as for the recycle time this depends on how important it is to you, if you were shooting lots of fast fashion shots one after the other then a fast recycle time could be useful but if like me I only take at fastest about 1 picture every 2 seconds because that’s as fast as my camera can shoot so I’m not that bothered about recycle time. I’m concerned with flash duration though for freezing moving subjects sharp and that is the subject of one of the videos in this section.

  6. Hello Karl,
    I’m an amateur who has recently gotten into food photography. I’m interested in moving from speed lights to studio lights. My question has to do with ambient light. I don’t have the luxury of a modeling light and I have always started out by first determining my aperture followed by adjusting shutter speed to eliminate ambient light. Then of course I adjust the power settings on my speedlights. How do I handle using a modeling light? And is eliminating all ambient light really necessary?
    I love your videos, they’ve helped me very much. Please keep up the great work!
    Dave

    1. Hi Dave, glad you are enjoying the classes. The question you have asked is answered in full in 2 classes along from this one in the lighting theory section ‘relationships of shutter speeds and apertures with flash’

  7. Hello Karl,

    Thank you very much for such a deep and informative knowledge. I was searching for some lesson alike and really happy that it lead me to your educational platform since I am about to by my first studio flash light and I really wanted to know what power of the flash light would be enough for my beauty and fashion photography. I see that in the one light set up lessons you are very often using Broncolor Siros 800. However, at the moment my budget is a bit tight for Broncolor, therefore, I am choosing between Elinchrom ELC 500 and Godox AD 600 pro, my worry is if this power would be enough to create some sharp beauty images with camera set up of ISO 100 Sutter speed 1/160 and aperture f/16 (and lower) for example. I want to invest in a solid light system and I am very confused about my final decision, even though I have already worked with both brands before. I also know that you have been an Elinchrom user before, I would appreciate any piece of advice from your side. Thank you in advance!

    1. Hi thank you for your kind comments. Yes 500 or 600 will be enough for most of what you need. Remember that 500 at 200iso is the same as a 1000j light at 100iso. So you always have the option to increase your ISO to 200 and that isn’t going to cause you any problems. The next thing to consider is that I very rarely use my lights at full power so even if you see me using a Scoro which has the capability of 3200j on power 10, if I’m using it on power 7 then I’m on 400J.

  8. Hello Karl,

    Thank you for the amazing sessions. Have followed them and have some questions :

    1) in a fast paced environment – such as wedding ? there is no time to keep checking flash power ? How to know how to use correct setting of off camera flash. Am using Godox AD200 and sony A7iii

    start with more power in flash and then reduce it ? whats the correct order to follow ?

    Please guide. Thank you

    1. Hi, Once you have a certain shooting distance and the correct power then you won’t need to change it much for any other shots at the same distance. So one way of doing it might be to run some tests and you can work out that at 2m the flash power is X, at 3m the flash power is Y, and at 4m the flash power is Z. Of course this can still be tricky which is why for weddings with lots of things changing distance quickly then photographers often use flash with TTL instead. But for static setup shots such as the formal portraits I would use the flash manually.

  9. Hi Karl, if I understand correctly, it is probably not technically possible to take pictures indoors with an aperture of less than f4 because ambient light is given, only this can be compensated with an ND filter. If I want there to be bluray in the background and also a lot of light and flash is on the power number 2 how can this be solved ..? By the way, I would like to use only one light.

    1. You could always use a light that has HSS (high speed sync) so you could use a shutter speed higher than you cameras max flash sync speed. This will allow you to cut your ambient exposure with faster shutter speeds.

  10. I am looking to buy Godox strobes (as I already own their trigger and a continuous) and the difference in price to go above 400w is quite a lot. I can’t tell if I will need them or not. I am looking to shoot product photos (still subjects) in a small 10′ x 15′ room with a lot of natural light. I have a Godox FV150 which is a 150w LED continuous with a strobe function. With this light by itself I can shoot at up to f5.6 on my Sony A7III at ISO 160.

    I’d like to buy two 400w strobes but I could spend more and get a 400w and an 800w (don’t know if that would be advisable) or two 800w. I don’t want to buy lights twice but I don’t want to waste money either. 800w lights are more than 2x the price for the 400ws. What would you recommend?

    1. Hi, if you’re going to use continuous light for your product photography then you are going to need to make sure there is no natural light coming into your space or you will loose control of your lighting (unless you deliberately needed natural light for say a food shot or similar). 400w is only one fstop less than 800W so you can probably save money and go with the 400w and turn your ISO up one stop would make them equivalent to 800w.

  11. Can you just increase the amount of power and not afraid to damage the flash light itself? In other worlds, are there limits to the power that flash light can sustain?

    1. Hi, the limit of the flash power is how many W/s or Joules it says it is capable of so for example you might see a light with 800 on the side which means it’s maximum output on full power is 800J but then you may find a more expensive light with 1200J at full power. On full power they can’t put out any more power so the flash is designed to handle that power. On some big packs like a 3200J pack you could accidentally plug a 600J light into it and damage it but that is not common as when you buy such a pack you know what type of lamp heads to buy for it.

  12. Hi Karl,
    i would like to know how to convert joules to watts because the lamp I am using is 60 watts but it does not show the joules.
    Thank you.

    1. Hi they are equivalent as far as the number goes although Joules refers to energy rather than power. But a 800W studio light is the same as a 800J studio light. I don’t know of any studio flash that is only 60W or 60J though?

  13. Hey just wondering, is there a reason you put an nd filter on the lense rather then over the light?

    1. Hi AdamF516, it’s just generally easier. We do have ND filters for lights but often we are working with more that one light and if we need to reduce power then we’d have to ND gel all the lights.

  14. Hi Karl,
    Thanks for the great lessons.
    I use Godox AD600 pro with 120 cm Octabox. I need to get an equivalent amount of light as your example if you were using an 800 light on full power at f11 ISO 100
    Thanks.

    1. Hi, your 600 godox is half a stop less than an 800 light so by increasing your ISO by half a stop would be equivalent.

  15. Hi Karl,

    Thanks for making this class enjoyable and so comprehensive. Forgive me if this question has already been asked, but I wonder how you typically determine which Aperture to use when shooting in a studio against a specific background. When shooting outdoors, I usually know I want to use the widest aperture when shooting a portrait and a smaller aperture when shooting landscape for example– when shooting in studio against lets say a white or red background, what difference does is make in terms of depth of field? I am never sure what aperture to use and if it has any artistic value to have it one way or another. Any clarification would be greatly appreciated. Thanks!

    1. Hi Kelloosh, ideally the aperture is the first creative decision you should make. For example if I’m shooting products or fashion where I need a good depth of field and pin sharp clothes and skin I will go for f16. If i’m shooting a portrait close up and I want to soften the ears and back shoulder then I’ll be at f8. Then everything revolves around that, you simply adjust the power of your lights and/or ISO to suit the aperture you selected. The shutter speed is largely irrelevant when used with flash as you will see in the following classes.

  16. Hi Karl,
    Thanks for the great lessons. I learn a lot.
    I use Godox 200 with 120 cm Octabox. Do you think it is enough power to “fill” this box with light?
    Thanks.

    1. Hi Thank you. It depends on many factors such as shooting aperture, ISO used, distance etc. Just remember the power of lights is in stops just like ISO or Aperture full stops so a 200 light is one stop less than a 400 or two stops less than an 800. So to get the same amount of light as an example if you were using an 800 light on full power at f11 ISO 100, then with a 200 light you would be at f11 at ISO 400 or at f5.6 at ISO 100.

  18. Hi Karl,

    How about flash lights that don’t have large power spread? Like a maximum of 3 and a minimum of 0.1.
    Is the rule of 1 full decrease equals a full F-stop decrease still representative? Or do you need to divide the total amount of stops your lens is capable of by the amount of power the light can bear and do some calculation to match a 10 range light?

    Loving the courses, especially the business ones!

    Thanks in advance,
    Alexander

    1. Hi Alex, nearly all studio flash lights are designed to work in quantities of an f-stop. For example many years ago before flashes were as precise as they are now, many were only available to change in 1/4 or 1/2 stop adjustments only. As technology improved 1/10th of an fstop became common. As far as I’m aware (regardless of total range) nearly all brands operate that one whole number change equals one f-stop change. As I don’t know which brand of lights you’re talking about I would say your best bet is to take a picture with the lights with the camera at f8 (shutter speed at highest sync speed in a relatively dark room). Then put the lights up by one full number (for example from 2 to 3) then close the aperture on your camera from f8 to f11 and if the exposure looks about the same then you know that the power of the light changed by one stop.

      1. Hi Karl,

        Thank you for your comment & advice! I’ll definitely try it out!

        I’m in possession of a very basic set of lights: Godox E300. It’s not high quality but sure does the job finding what suits best for me and to go from there for future decisions. I’ve been able to work with the Profoto b10’s and man are they lovely to use. Such creative freedom! But still quite out of the budget haha. Therefore, I’ll be looking for something in between as an intermediate level which still has a good power range for its market price.

        Any recommendations by coincidence?

        1. Hi Alexander, I can only recommend brands we’ve used which are Elinchrom (good middle of the road) Profoto (good but more expensive) Broncolor (top but expensive). I’ve got a couple of Godox 600s that seem OK but I’ve not used them much we only purchased them to show in our videos that other brands can be used to yield the same results. 600-800s are plenty powerful enough for most people and if the power doesn’t drop low enough then a good ND filter on the lens will do the trick.

  19. Hi Karl,

    First of all, this series about how light works is fantastic.

    With the same aperture, is there a difference in the illumination on the distant background when using a light on power 5 with a 3 stop filter as opposed to using it on power 2 with no filter? I tried comparing the images on the video and it looked slightly different but I wasn’t sure it was due to video compression.

    Cheers.

    1. Hi Squiggle, Power 5 is 3 stops brighter than power 2. The ND filter would remove 3 stops of light so it would be exactly the same in all respects as on power 2 with no filter. The only slight discrepency can be sometimes that when reducing the power of lights they might not be exactly the amount you requested but usually they are very close.

  20. Hi Karl. Really enjoying all the content.
    I have a question. Im starting put with my own home studio, and I am using just the light of my flashes. As it happens, if I take out the picture without the flash, my pictures are a black because I have taken all the ambient light off with my camera settings. At the time I cannot afford a light meter, so is there a way to know how to get the correct exposure before taking the picture? I do not trust my camera lcd display and it obviously takes too long to take the pictures into my laptop just for checking the exposure, I’m also not tethered to my laptop. So as I said, if I try to expose with the camera light metering, it will be surely underexposed before the flash do its work. Is there something I can do to try to get the exposure and light power correct without having a light meter. Of course Im going to get one as soon as possible.
    Thanks a lot for your classes and you patience with all this questions.
    Greetings from Mexico!

    1. Hi Momo, yes this should be relatively easy. First of all set the desired aperture that you wish to use for creative depth of field. Let’s say that’s f8 for example. Then you have your shutter speed to block out ambient light and that shutter speed can be set up to the maximum sync speed which is usually around 1/200th of a second. Then you have ISO which the default is usually 100. Now if you take a picture with no flash or other lights the picture will be dark. Put the flashes into full manual mode and now you will be able to set their power between 1/1 (full power) or 1/2 (half power) 1/4 (quarter power) and probably all the way down to 1/256 power. Start on 1/16th power and look at the result, if it’s too dark go up to 1/8th power if it’s too bright go down to 1/32th power – It’s that simple just think of the manual power up or down just like turning the sound up or down on your radio until it sounds/looks right.

  22. Hi Karl, I have one strobe light Quadralite ATLAS 600 PRO TTL (600Wat). I’m using it in home studio which is rather small, about 20m2. Would you recommend to use the same power strobe light for fill light as the key light ? Would be better for controling a effect with lights of the same power ?

    1. Hi, it doesn’t really make any difference if I had a 300W lamp then I know it’s one stop less powerful than a 600 but I also know I can turn the power down on a 600 by one stop so resulting in the same power, or put an ND gel on them or a different modifier. All of these things (as will distance) affect the power of the light.

  23. Two last questions Karl. In terms of distance (in m or cm) what will be equivalent to 1 stop of light difference? Does the brand of the lamphead affects this? (I guess 400j it still should be 400j independantly of the brand…but im still asking this because with all your ears of experience maybe you have seen some exceptions or particular cases).

    1. Hi, it depends on the modifier you are using but two different brands with 400J with the same modifier should put out the same light but often it’s not the case, I’ve measured the values and they aren’t always equal! The power of the fall off in light based on distance also depends on the modifier used as they all spread the light differently but as an example with a bare bulb light (no modifier) if you move it twice the distance away it will be 2 stops less powerful. – https://en.wikipedia.org/wiki/Inverse-square_law

      1. Yep, I asked the question too soon…learned this in the next chapter but thanks anyway for your reply 😀

  24. Hey everyone! probably what I’m going to say is obvious…but anyway, by watching the chart of aperture values that indicates 1 stop of light change I realized that I only need to know the first two : f 1 and f 1.4 for knowing them all, the following values are just the double of the number before the last aperture value:

    The next value in the sequence will be f 2 because the number before my last aperture value is 1 and 1 x 2 = 2. Now I have f 1, f 1.4 and f2, then my next aperture value will be 2.8 because now f 1.4 is the number before my last aperture value and it continues the same way: f4, f 5.6, f 8, f 11 (which will really be f 11,2 though guess in this point it was rounded to the nearest tenth), f 16, f 22, f 32, f 44, f 64 and so on (I don’t know if the last 2 values actually exist on cameras but I guess it will be like that).

    1. Hi, yes this kind of works, the last two values are f45 and f90 so it still works but their are of course the half step apertures inbetween these. You’ll find in time that you memorise all the numbers anyway! 🙂

      1. Oh I see! well now it totally make sense for me, at f 11 it was rounded to the nearest tenth, remember the value I said it should of been was 11.2? If you continue with the same process but without doing the rounding, the values will be the following: f 11.2, f 16, f 22.4 (rounded will be 22), f 32, f 44.8 (which rounded will be 45), f 64 and f 89.6 (rounded will be 90) 😀 … But yes, you are totally right Karl, sooner or later I will end up memorizing all these numbers 🙂

  25. Hi Karl!
    I have a question…
    How much flash power does one need for product photography when photographing in a small home studio? I was thinking of buying three lamp heads… should I get them in different powers?
    Thanks in advance!

  26. Hi Karl,
    Really enjoying the training so far. So you’ve explained how using an ND will help get the desired DoF & correct exposure when constrained by the low-end power of the light unit. Without looking at the cost difference between a 400j and 800j light unit, my initial thoughts when constrained by the high-end power would be to fix exposure by using ISO. Modern cameras deal with an increase of 1 stop ISO no bother when at the lower end of the range like you are at ISO 100.

    I don’t think this was covered in the video (if it was my apologies) but is there any impact of this besides image quality and risk of introducing a little bit of noise?
    Cheers,
    Tom

  27. Hi Karl!
    I am thinking of investing in a home studio, to start to shoot products.
    I have a Canon camera (t5i)
    I don’t have such a wide budget and was wondering what brand of flash would you recommend buying for the beginning. Should I buy a strobe flash + a normal one? What’s most crucial and useful as a beginner?
    Thanks in advance

    1. Hi HC, I’m afraid we are unable to make good recommendations on equipment that we haven’t used. The top brands are broncolor, profoto, other reasonable brands could be Elinchrom, Godox.

  28. Thanks Karl for a another fantastic tutorial! Query: Are all better caliber studio lights adjusted manual during a shoot or can they be adapted TTL metering some how? Or better question: Should I be using my setup with manual power settings rather than TTL? I am presently using a 2-speedlight setup with softbox modifers as I am just getting into studio indoor work. Thanks!

    1. Hi I would say from a learning perspective get into the habit of using them in full manual and forget TTL. Most studio lights don’t have or need TTL you just set the power based on what you see in the same way you control the volume on your ipod based on what you hear.

  30. Hi Karl this was very helpful and clear to follow. You teach in a very pleasant and comprehensive way about each topic.

    I have one question regarding product photography lighting set up. is there a lesson or a video you created which explain the ideal light set up for a home based studio for Product Photography?
    thanks.
    Angela

    1. Hi Angela, yes we have lots of product photography videos in the ‘product’ section head to the top menu and browse through those classes.

Leave a Comment