A relatively recent debate has arisen on the internet about the type of lighting we use. Traditionally photography has used all strobe, all the time, as tungsten film lights are very heavy, power-hungry and expensive. But now that the costs of continuous lighting are starting to fall and we're seeing more and more high-power, full-spectrum, daylight-balanced lighting sources come to market, is there an advantage to using continuous lighting in your work?
Perhaps you're new to lighting in general, and are looking at how to get the most bang for your buck, or the shallowest learning curve. In this article, I'm trying to give a solid overview of the options out there for you, and the criteria to use for making a decision. Today, we'll compare the advantages each system has.
Strobes will give you far more useful lighting power than continuous for any given cost, size, or whatever other constant variable. Why is this? Because a continuous light has to reflect photons off the subject and into the lens for the entire duration of the shutter opening. Strobe, however, can pack as much power as it likes into a very short space of time, and it's quite easy to release lots of energy instantaneously.
Let's do a little simple math to illustrate the point. If you have, say, five 60W incandescent light bulbs, you should have somewhere in the region of 5500 lumens of light at 17-18 lumens per watt of input power being emitted from them in all directions. Because it's continuous, each and every second, that 300W setup is therefore putting out 5500 lumen-seconds of light. A lumen second is a measurement of total output of light regardless of duration.
Take a strobe, with its xenon gas discharge tube, which attains somewhere in the region of 300 lumens per watt. Let's use a relatively low-power 60Ws speedlight, and assume the manufacturer isn't fudging the numbers and the electronics are high-efficiency. If we multiply the lm/W by the Ws, we cancel the Watts and end up with lumen-seconds. So the lumen-second output is around 18,000lm-s.
Well that's quite a bit higher than the continuous lights! Yes, but, remember: all of those lumen-seconds from the strobe are being discharged in around 1/2500 second. So we take the lumen seconds, divide by seconds to leave lumens, and what do we have?
18000/ 1/2500 = 4800*2500 = 45,000,000 lumens! Realistically the output from flashes is more like 10,000,000 lumens, due to optical and electronic inefficiencies, but still. They're all hitting your subject almost instantaneously, allowing you to very briefly overpower the sun, very briefly light up whole rooms or hillsides or waves. This is still photography. We only need a brief moment to capture an image.
Since energy = power x time, the 160Ws strobe stores 160 Joules of energy in its capacitors, where the 300W of tungsten lighting uses 300J of energy over the course of the one second exposure. Twice the power, a tenth of the lighting ability!
Thus, if you want large quantities of power for large work or you'd like to be able to overpower daylight, the best course is to use strobe.
Strobe allows you to have a sun in a body the size of a can of coffee. You can light up rooms like midday with a strobe that fits in your hand and weighs a few ounces. If you do, or are planning on doing, a lot of location shooting, strobe is pretty much essential.
To generate the same kind of lighting power as a strobe using continuous lighting, you'll need to resort to multiple high-power Fresnel HMI lights, running at 4-20kW, weighing about 50-60lb each, and costing thousands of dollars, yet only generating around 100,000-500,000 lumens. This combination of power and convenience is why strobes still aren't going to be displaced any time soon.
In terms of size-of-light, four-foot fluorescent tubes don't pack down into a small footprint, and in fact need lots of impact protection, adding to the bulk. On the other hand, a 48x36" softbox will happily disassemble into a relatively tiny area.
3. Battery Power
For both strobes and speedlights, small battery packs are a legitimate power source. LED lighting is improving constantly so that there's a realistic battery-powered continuous solution, but it comes nowhere near the size or power that's attainable from strobes for still imaging. With batteries, you can go anywhere and take a three, four, or five point lighting solution with you. For location work, this is indispensable.
Speedlights can use regular AA batteries, or you can plug in a high-voltage external pack in for faster recycling times. Lithium battery packs with built-in inverters are available to take your studio strobes anywhere, just like speedlights. This is especially ideal for small, tough strobes like AlienBees.
The spectral distribution of the output of xenon discharge tubes is such that their "Colour Rendering Index" or CRI is effectively 100. CRI is a measurement of how well a light illuminates colours without shifting them due to spikes or troughs in its colour output.
The closer it can get to outputting a continuous spectrum, regardless of temperature, the better. Tungsten is also 100, but other continuous lights like tungsten halogen, full-spectrum fluorescent, or LED are all CRI 95 or less. If you're looking at continuous lights, by the way, 80-90 CRI is "good," 90-100 is "excellent." Generally look for lights that are CRI 91 or above.
As well as being perfect at rendering colours, xenon flash tubes are coated in such a way that the output is colour balanced to 5500K daylight, making them very easy to work with in a variety of conditions, adding to the slew of convenience we're witnessing here.
The cost per lumen-second (or watt-second, or lumen for that matter) is much lower with strobes. This is largely down to the power and colour requirements, which are really quite difficult to do at reasonable cost right now with continuous lighting.
Fluorescent seems to be the most effective, with T-5 tubes reaching 5200 lumens each at 93CRI, and photographic compact fluorescent bulbs reaching 4800lm at 91CRI.
A decent manual speedlight can be had for under $100, and TTL for around $200. Four of the high-power full-spectrum T-5 tubes costs around $35, not including the fixture and electronics to run them, which adds up to another $150 or so. That's if you build it yourself.
Cool Lights and KinoFlos are more in the $500-1500 range, and don't match the power of the speedlight. A 160Ws strobe can be had for less than $250. Adding the cost of a 12x48 stripbox to match dimensions, even a Lastolite model won't bring you up to the price of a good quality fluorescent fixture.
Well, it looks like strobes have well and truly demolished continuous lighting across the board. But have they? We haven't yet looked at all the factors. Let's look at some advantages of continuous lighting.
"What you see is what you get." With continuous lighting, there's no need for modeling lights, which run very hot and can limit your use of modifier. However the scene looks to your eye will be how it appears on camera.
This can be a big bonus when learning to use artificial lighting, since you can move the light around and get instant visual feedback without having to shoot anything at all.
Lighting ratios are right there in front of your eyes. No flash meters, no particular need to shoot manual, just flip switches until you like what you see, then adjust aperture and ISO accordingly. That's as soft a learning curve as I can think of!
What the subject sees is also what they get. No blinking or disorientation from popping strobes all over the place, just an initial adjustment to the unusually high light levels.
2. Do It Yourself
If you're DIY-inclined, it's significantly easier, safer and potentially even cheaper to go the continuous route. A DIY four-foot fluorescent fixture can be built for around $150-200. Multiple high-power CFL fixtures in a large enclosure could run around $200-250.
Comparing this to buying strobes, the price is comparable or even slightly lower. Comparing it to trying to disassemble, modify or building strobes, the safety factor is night and day. No high-power, high-voltage capacitor banks to worry about, or insulating discharge paths.
While it may be possible to build strobes for low cost, unless you're an electrical engineer, it may well be best left to the experts. Just remember that fluorescent tubes contain mercury vapour!
Even if you're not DIY-inclined, the potential for "alternate use" in continuous lighting is great. Want a KinoFlo? Buy a $150 grow light. Want as many lights as possible? There's no shortage of old light fixtures and lamps available used for a couple of dollars. Unlike strobes, there's no reason why you must use the lights specifically designed for purpose. While they will be far more useful for photography, they're also a major investment.
3. Low-Power Advantages
The lower power of continuous lighting isn't always a disadvantage. If you like to shoot lit, but wide apertures for depth-of-field effects is your style, continuous is a good way to go.
If you shoot food, product, still life or other stationary subjects, the aperture isn't even a worry, since you're not generally limited to action-stopping shutter speeds. The lighting can be adjusted and shifted to your liking, and whatever the shutter speed is doesn't matter too much. This is possible with strobe using a variable ND filter, but it's good to be able to see to focus!
4. Quality of Light
This one is quite subjective, and it could just be me, but have you ever noticed that there's a subtle difference to the quality of light between diffused strobes and spaced continuous lights? It may just be me, but I've always found continuous lighting to have a slightly more pleasing quality.
Perhaps because it's "true" diffusion with consistent power over the area instead of a fall-off towards the edges of a strobed diffusion surface. This is certainly true of fluorescent tubes, anyway. LED panels are generally not large enough to be able to see the effect yet, but I imagine the same holds true.
They say that light is light, and from a physical standpoint, I agree. But there's still a soft crispness to continuous light that I can't quite put my finger on.
The video aspect of continuous lighting can't be overlooked, particularly these days when more and more photographers are being asked to double up as videographers on HDSLRs. Having video lighting ready to roll from your stills work can be a valuable asset to a potential client with broad needs.
You'll also be practiced with rigging the continuous lights and how subjects look while moving around in front of them, putting you half a step ahead of photographers shooting only strobes.
Which to Buy
Honestly... I say both. Each is really a different tool for a different purpose, and as you see from the pictures, I'm working on adding the continuous aspect right now. You can even sometimes use both at once: light painting with continuous while freezing the participants with second-curtain strobe, for example. Another situation might be headshots with the now-popular continuous light setup for the subject's eye comfort, while strobing a white seamless background.
Otherwise, it depends on your particular needs. Do you need power and portability above all else? Then go with strobe. Are you tied to the studio and rarely go above f/3.5? I'd say continuous. Your particular situation is likely more nuanced than that, though, so I can't really offer any one-size-fits-all advice on the topic. However, this tutorial should give you some insight on the topic, and help with your decision.
Questions? Comments? Hit up the comments below!