Comparing strobe and LED flash duration

May 10, 2023

Jake Hicks

Jake Hicks is an award winning editorial and fashion photographer who specializes in keeping the skill in the camera, not just on the screen. For more of his work and tutorials, check out his website.  On Jake’s Facebook page, you can also tune in for a live stream every other Tuesday night. You can also sign up for the Jake Hicks Photography newsletter to receive Jake’s free Top Ten Studio Lighting Tips and Techniques PDF and be sure to download his free 50-page studio lighting book.

Comparing strobe and LED flash duration

May 10, 2023

Jake Hicks

Jake Hicks is an award winning editorial and fashion photographer who specializes in keeping the skill in the camera, not just on the screen. For more of his work and tutorials, check out his website.  On Jake’s Facebook page, you can also tune in for a live stream every other Tuesday night. You can also sign up for the Jake Hicks Photography newsletter to receive Jake’s free Top Ten Studio Lighting Tips and Techniques PDF and be sure to download his free 50-page studio lighting book.

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Comparing strobe and LED flash duration - featured image

We rarely see any big changes in the flash lighting world, but one area that is constantly evolving rapidly is LED lighting. One of the more interesting innovations we’ve seen come out of that field is LEDs that can also flash. But what does that really mean? How are LEDs actually flashing and is it a feature you need?

As many of you know, I’m currently a ‘Master of Light’ for Rotolight who are a U.K. based LED lighting manufacturer. Essentially that title means Rotolight deem me decent enough to use their lights to their fullest potential and that I have the ability to share my thoughts on them via socials and in-person training. But why on Earth would they choose me? After all, for the past 20 years I’d been happily using my flash heads alone, I’d never really used an LED light before and for good reason. Until now.

Comparing strobe and LED flash duration - images from the last 20 years
I’ve been using studio flash for 20 years, why change to LED now?

In the past, I’d always felt LEDs were a far-cry from being the ideal solution compared to flash for several reasons, paramount among them, being their limited power unless you spent a ton of money. The white light from older LEDs was often a sickly green instead pure white and the LED colours themselves were usually muddy and indistinct. Yellows were often light green and the reds were closer to dark orange than an actual rich red colour.

As a heavy colour user myself, this was a complete no-no, but it wasn’t until a chance meeting at a studio a little while ago that I got to witness what the Rotolight LEDs could do and I was instantly impressed.

I’ll save my tribute and shopping list of reasons as to why I was immediately blown away by these lights for another time, but suffice it to say, elements like unbelievably clean-looking light, gorgeously deep and rich colours and a very usable brightness for almost any situation certainly got my attention. Of course, the one other feature that really got my attention was their ability to also flash.

LEDs that Flash

So what are LEDs that flash? In short, the LEDs in these lights essentially overclock themselves for a very brief moment to give you a very bright burst of light. The LED bulbs can’t sustain that brightness continuously without substantially reducing the lifespan of the bulbs, but they can happily give you incredibly fast bursts of flashes with zero recycle time for a sustained period with no issue or overheating worries.

Rotolight
Me working with the Rotolight AEOS 2 Pros at a recent lighting event.

As I mentioned, this tech has been around for a little while now, and although a few companies are using the flash feature for white light, Rotolight are still the only LED lighting manufacturer that can flash their LEDs in the complete 16 million+ RGB spectrum! Now you’ve got my attention.

What are the benefits of having LEDs that flash?

To be honest, one of the greatest features of LED lighting is just how unbelievably simple and easy the continuous lighting make lighting in general. Why on Earth would you give that continuous light up to use flash when you can quite literally see exactly the type of lighting you’re going to get before you even hit the shutter? No more guessing how the flash will look and couple that with the electronic viewfinders (EVF) of many modern cameras that show you the exact scene for your given settings, it really is ‘what you see is what you get’.

Photography has NEVER been easier than it is today.

So again, why give up the cheat-code of LED lighting for the flash mode? One big reason (and I can’t speak for other LED brands), but the Rotolight flash mode actually doubles the brightness of their ambient mode LEDs. That double brightness can certainly make a big difference in a shot, so even if you only use it for that feature alone, having a double-power button is always worth having.

Of course, the other core reason any of us would use flash is to capture movement.

Capturing Movement

Most of you reading this now are likely flash users, you know all about capturing movement and how flash is the best way to do this. We know a faster shutter speed will easily capture fast-moving objects and render them stationary in the shot and we all know that flash is a very fast burst of light that captures moving objects too.

comparing various shutter speeds on fast-moving fan blades
Click to enlarge: Examples of various shutter speeds on fast-moving fan blades.

So, the faster the shutter speed, the more stationary the object is rendered in shot. The only drawback to very fast shutter speeds then, is that it requires a lot of light to still capture that object when the shutter is only open for a tiny fraction of a second. This is where flash is great. We don’t have to worry too much about the shutter speed now, because as long as the flash fires when our shutter is open, we’ll have a burst of light that is very short and that will capture the subject.

So to summarise; to capture something moving, we can either use a very short shutter duration or we can use a flash as that burst of light is also very short.

Flash Duration

So how fast actually is a flash? It’s very easy to understand how long our shutter is open, after all, we can simply look at the camera display and many modern cameras today are very comfortable shooting at 1/2000th of a second, 1/4000th and even 1/8000th of a second. But what about flashes, how fast are they really?

flash light cycle

This is where things can get a little overly complicated as contrary to what many people think, flashes are not instantly bright and then instantly dark again. So to explain this, let me briefly show you how some typical flashes work.

Many flash units will have a glass tube filled with Xenon gas. This tube of gas is then ionised via an electric trigger and a very bright spark is formed between the two electrodes AKA the flash. As this is a chemical reaction, there is indeed a build-up when the gas is triggered and the resulting light is formed. Again, this light must then dissipate and although seemingly happening instantaneously, it is in fact taking a period of time and that period can vary from flash to flash. Some flashes have a duration of 1/500th of a second and others are much faster at 1/4000th of a second and beyond.

But here’s the bit that gets a little more complicated; how do you measure that flash duration?

Measuring Flash Durations

Because of this build-up and taper-off, flash lighting manufacturers had to agree on a way to measure the duration of their flashes. Do you measure the time from when the spark ionises the gas? Do you measure it from when the light has reached maximum brightness? Do you measure from spark to total dissipation? You can see how this would be confusing.

Ultimately flash durations are measured on a bell curve like we see on the diagram here and most flash manufacturers quote the T0.5 value as the duration of their units.

The T0.5 value is the time it takes from when the flash reaches 50% power, up to 100% power and then drops back down to 50% power.

flash light output depending on T0.1 and T0.5

When I first discovered this, I was very surprised, because as you can see from this curve here, there is an awful lot of time which is not measured in the ‘flash duration’ measurement, but the flash is still very visible. This did explain to me why I was getting movement in my photos when I thought I shouldn’t, especially when I was using a flash that supposedly had a flash duration of 1/4000th of a second. The manufacturers weren’t lying about the durations of their units, they just didn’t have to include all of that extra time the flash was active.

If you wanted a clearer representation of the duration of your flash, you should really be looking at the T0.1 value as this is measured from when the light reaches 10% power, up to 100% and then back down to 10%. Many manufacturers have this data, you just have to seek it out. At the very least, you just need to be aware of what the T0.5 means and just be aware that your flashed scene will be receiving a lot more light than you originally thought.

Does it really even matter?

It feels like we’re splitting hairs here right? Surely we’re being overly nerdy about flash durations for no reason. Yes, for the most part, nearly every modern flash unit’s duration is incredibly fast and for the vast majority of us, these flash durations are absolutely fine. Unless you’re photographing toddlers or hummingbirds, you’ll likely not notice any movement in your shots. That being said, fast-moving dancers, clothing flowing about and hair blowing in the wind of a fan, can actually display movement in the final shot. It’s one of those things you don’t really notice because it’s always been there, but once you see it, you sadly can’t stop seeing it.

Of course, there are other faster-moving things like water and falling objects in still-life photography where pin-sharp and crisp motion are paramount. So to test the flash durations of my strobes versus the flash duration of my Rotolight AEOS 2, I decided to drop some metal ball bearings (actually cheap cake decorations!), onto a metal plate. During the time these silver candy balls were bouncing off of the metal plate, I would fire the flashes and capture the results.

metal balls - I  am about to bounce those

Testing and Comparing the Flash Durations

For clarity, the test was performed with a single studio strobe and single Rotolight. The shots were taken against a sheet of black velvet and the camera was mounted on a tripod with a 70mm lens.

All of the photos for both the studio strobe and the LED were captured via a flash trigger and I tried both high and low power outputs of both to see how that affected the results.

Resulting Images Captured with the Studio Strobe Unit

Flash fired at high power
Flash fired at high power
Flash fired at low power
Flash fired at low power

Now let’s do the same test but with the LED light.

Resulting Images Captured with the Rotolight AEOS2

Rotolight AEOS2 LED fired at high power
LED fired at high power
Rotolight AEOS2 LED fired at low power
LED fired at low power

Conclusions

Look, I’m going to be completely honest here, I had an inkling that the LED shots would be crisp, but I certainly wasn’t expecting this comparison to be anywhere near this conclusive! You don’t need to look too closely at these comparison photos to see the very stark differences between them. The LED shots are damn-near crystal clear (these images are all shot on a Nikon and with a Nikon lens, so trust me, this is clear as it gets), compared to the huge amount of movement we see from the flash images. Also, there’s a big difference between the amount of movement at higher powers on the strobe due to how the strobe units work too. But why is there such a big difference between the strobe and the LED?

Breaking it Down

Earlier on I explained to you how a flash tube worked. I said that a flash is triggered by a spark that ionises Xenon gas that in turn displays a very bright light before dissipating. I then showed you a diagram of that curve of light as it rises quickly before peaking and then finally trailing back down. This is why we see those ‘tails’ of light on those bouncing metal balls in the resulting shot, this is the flash dissipating and trailing off leaving that ghost of an image behind them.

But what about the LEDs? How do they ‘flash’? Thankfully, this is actually where it gets very simple. LEDs are simply powered via an electric charge and as we know, electricity moves extremely quickly. So just like you turning on a light at home, the light is (almost) instantaneously on and it can also be turned almost instantaneously off again. This is the ‘flash’ of an LED and I mocked up an example of that same bell curve diagram here just to illustrate the path that LED flash takes compared to the strobe version. As you can see, it reaches maximum power output instantly and then reaches zero output instantly again too due to the electric current being flipped on and off. I may have even exaggerated how long the flash is present in this diagram too. Put alongside the strobe curve, the LED flash could even just be a singular vertical line going straight up with almost no duration at all.

Strobe T0.1 vs T0.5 for Rotolight AEOS2

To be clear, I want to point out that this is just me experimenting with my lights with rudimentary-at-best parameters. This was far from a scientific test, but even with the basic results that I captured, it was pretty clear to me that the LED flash is no mere gimmick or feature to include on the side of the box. The LED ‘flash’ function of the Rotolight is an extremely viable tool.

What Does This Mean for Photographers?

At this stage, some of you may be thinking, ‘So what Jake? I bought my LEDs for an easy-life, I wanted to leave the finicky world of flash behind me and embrace the painless pleasures of ambient light’.

I’m right there with you, like I said, ambient lighting is just so easy I almost feel guilty of cheating like this. And now that LEDs are bright enough, the white light is clear enough and the colours rich enough, I have zero issue using LEDs over flash. But there are things that only flash can do and obviously one of those things is capture stuff in motion, and in some of my work, I also like to take things one step further and combine both ambient and flash in the same frame. With these new Rotolights, I can do just that.

Take a look at some of the mixed-lighting shots below, all captured in a single frame with the new Rotolight LEDs. Some of the Rotolights are set to ambient, and some of them are set to flash and triggered from my camera like normal.

Click on any of them to fit them to your screen.

As you can see, the Rotolight’s ability to both be used as an ambient light and a flash is completely unique, especially when you consider that it can flash in the full Kelvin spectrum and any of the 16 million+ colours too. Couple that with its ability to capture movement like this in pin-sharp clarity that not only rivals flash, but supersedes it, it is fast becoming the only light I need!

Final Thoughts

As you may well imagine, I was blown away by the results of the Rotolight’s ability to flash. Sure, we already have hundreds of flash units on the market today and people usually tend to buy LED lighting for film and video as they want that continuous light for motion video. But Rotolight is one of the very few LED manufacturers at the moment who are making LEDs for photographers as much as they are videographers. With that in mind, they are making lights with more and more flash functionality than anyone else, like I said at the start, Rotolight LEDs are the only lights in the world that flash in the full 16 million+ RGB colour spectrum!

I’d wager that in 5 years, we’ll see all new LEDs coming to market trying to include this full-colour flash function, as a standard feature!

Plus, the actual flash duration and quality of that flash is incredible as I demonstrated earlier, so much so, that the flash on these units kinda needs its own name. Can you really even call an LED flash this unique, a flash anymore?

Tech Specs

Just briefly and for those that are interested, here are a couple of bullet points of info regarding the flash capability of the Rotolight AEOS 2 PRO & NEO 3 PRO.

Also, I mentioned before about triggering the Rotolight from my camera and with the new Rotolight PRO units, you can even combine them with your current strobes by triggering them from your current trigger. Those transmitters include:

  • Godox
  • Profoto
  • Elinchrom
  • Neewer
  • Pixapro

One last note is that not all of these features are exclusive to the PRO versions of the lights and most of what I’ve spoken about here is very achievable on the older AEOS 2s and NEO 3s and many of the example shots I’ve shown here are taken on those older units.

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Jake Hicks

Jake Hicks

Jake Hicks is an award winning editorial and fashion photographer who specializes in keeping the skill in the camera, not just on the screen. For more of his work and tutorials, check out his website.  On Jake’s Facebook page, you can also tune in for a live stream every other Tuesday night. You can also sign up for the Jake Hicks Photography newsletter to receive Jake’s free Top Ten Studio Lighting Tips and Techniques PDF and be sure to download his free 50-page studio lighting book.

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