“Continuous light” is a bit of a catch all term – there’s so many different types, that’s it’s probably best to think of continuous light as simply “not flash”. And that’s the best way to describe it – whereas flash emits it’s light in a very brief pulse, continuous light emits it’s light continuously.
Continuous Lighting – Types
There are so many different types, forms and brands of continuous light out there, that I couldn’t begin to describe them all in any usable depth. The main types you’ll come across though, are Tungsten lights, lighting based around flourescent tubes, and LED panels of some sort. Some of them can be mounted directly onto the camera, some can run off batteries, some will take a range of modifiers and adapters, but all of them still obey and exhibit those 4 basic characteristics of light that we talked about in so much depth earlier.
Continuous Light – the Advantages
Straight away, it’s clear that one advantage of continuous light is that there’s no need to sync the light source up with the camera in any way – just turn it on, point it at what you want, and away you go. Next, it’s much easier to see what effect your light is having, even down to things like relative power outputs – you can quickly spot just with the naked eye if a light is way too powerful, or if it’s casting shadows in the wrong place, or if the shadows are too hard.
The fact the light is always on also means that you can safely use continuous lights for video – so if you’re doing a shoot where stills and video are required, it may be a better option. Check exactly what type of light you’re using first, as some “continuous” lights are actually flickering or pulsing at a frequency we can’t spot with the naked eye, but that a video camera at certain frame rates can.
Continuous Light – drawbacks.
So what’s the catch? Why do I, for one, use flash much more often? Well, actually there are several reasons.
Power is one. Simply put, for the same size package, you get much more power output from a flash than from the same continuous light source. Both the lights in the video are 1kw in power output, but the fact that the flash emits it’s light in a very short pulse, allows me to get an exposure of 1/250s, f22 at ISO 100, whereas the continuous nature of this tungsten light means my exposure for the same scene is 1/60s, f4 at ISO 800. This is obviously more useful, and coupled with a wide range of power outputs in the flash head, means the flash is more versatile. Some types of continuous light comes with variable power, although it’s unlikely to be in the same huge 7-8 stop range you get with a decent flash. Many continuous lights don’t come with any power adjustment at all, which of course limits you a bit if you need to turn them down!
Power is also an issue in the sense of where the power comes from. There are lots of types of battery powered continuous lights, like this little LED panel, but they don’t really give much power, and are only useful for quite tight in shots like head shots. Most continuous light sources need to be mains powered – no problem if you find yourself in the studio or indoors all the time, but challenging if you’re working on location.
Temperature is a problem as well – in more than one sense. Firstly, in the literal sense – lots of continuous light sources can get very hot indeed. This can make them hard to handle, and difficult to attach things to – they can melt things like gels or modifiers that are attached to them. They can also be uncomfortable if you spend too long close to them – shoot with them indoors on a hot day, and you’ll see what I mean. You might be able to put up with this, but think about your subject, and how they’ll cope under hot lights. In some cases, your subject might decide on your lighting type straight away – let’s say you’re shooting an ice sculpture – 1000s of watts of tungsten light is probably going to melt it pretty quickly.
The colour temperature of continuous light can also be an issue. Tungsten lights have a colour temp quite low down the kelvin scale (think back to the 4 characteristics of light….). Fluorescent tubes can have a different colour altogether, and this will be a problem if you’re shooting under mixed lighting. If you’re primarily shooting in daylight white balance, for example, and you use a tungsten light to fill in some of the shadows, you’ll get an orange cast, as the light will be warmer than the colour temp you’re set for. You can add some blue gel to your tungsten light, which will bring it’s colour in line with the rest of your light, but you’ll have eaten up some of the power from the light, and as we know, continuous light doesn’t put out as much power as we might think!
Many modern continuous lights are daylight balanced, or can even be switched from warm to cool, so this is becoming less of a problem, but you’ll still need to be aware of it.
I’d still recommend you start building your lighting kit around flash, as it will definitely give you more bang for your buck, but don’t neglect continuous light.