If one were to want to get started with studio photography (I'm thinking things like portraits, headshots, perhaps pets, etc) what would be the considerations in choosing whether to go with continuous lighting vs. strobes for the lighting equipment?
- + More light means lower ISO, larger aperture etc.
- + Can freeze motion
- + Can overpower the ambient light meaning you can leave the room lights on to see what you're doing
- + Greater choice of flash units / accessories / lighting modifiers
- + Can be used with battery pack for location shoots
- - Have to be triggered somehow
- - Need to use a flash meter, or test shots to set exposure
- - Can be too bright (some have limited options to turn the power right down)
- - Can be more expensive to start off with
- + Can be done on the cheap using gear lying around the house
- + Can use the camera's metering system
- + Can be used for video as well
- + No need to trigger
- - Limited power output
- - Can cook your subject
- - High levels of ambient light can be undesirable when working
- - Fire risk with homemade mods!
- - There can be colour issues with some florescents
I'll give you my experience...
I started out using halogen continuous lights because they were cheap, but they're very hot and draw a lot of power. Nevertheless, I could get some very powerful lighting though, mind you, I went the "Home Depot" route here. What I discovered, however, is that I had no real effective way of performing light modification (filters, gobos, grids, etc.) without some fire risk. So, then I got a very basic Westcott setup that used highpowered CFL bulbs. The set came with two stands, the heads, and softboxes. Not bad, it seemed, but to get a decent shutter speed for photographing children, I had to pump up the ISO way too much for my liking, I prefer low ISO in a studio setup. These two options also suffered from a lack of control over the quantity of light and the duration of it and these are important factors in freezing motion and getting creative with lighting. They do, however, unhook your camera from the light, giving you some freedom of movement.
However, all of those weaknesses led me, finally, to strobes. I purchased a couple of Alien Bees B800 strobes, with stands and umbrellas, then added a softbox, an octabox, and grids. With these I was able to get far more control of the light, especially the duration and intensity. I hooked them up with basic radio triggers and I got the freedom of cableless movement that continuous gives. They do cost quite a bit more, though not especially so when compared with highpowered speed lights, but the flexibility was worth it to me and, I have to say, my buying experience with Alien Bees was second to none, they have my consumer endorsement if they want it.
Anyways, I still use the Westcott gear, it's actually quite handy for product type photography as well as background lighting and similar actions, I just don't use them as a key or fill light choice. The tungsten hot lights, however, are now back to general duty for a workshop, as I just wouldn't ever consider using them again. Admittedly, these were not dedicated for photography or videography, but I'm just not interested in pumping out that much heat for little to no gain.
So, just like the tripod trip from weak to strong, I suspect that if you start with the cheapest option, you will move up the chain and rapidly, and spend a lot for nothing along the way. If you're not willing to run out on the strobe cost right now, but you do have speed light of good power, you may actually want to start with reflectors to get bounce for fill and move up from there. At the very least, you'll still be using those reflectors when you do get the bigger guns which, I think, is inevitable if you enjoy the portrait process.
The heat's one thing -- and you can get around that with cool lights (fluorescent, LED or HMI) -- but the biggest difference for me is that continuous lighting needs to be pretty darned bright in order to use relatively low ISOs and reasonable shutter speeds. That's just uncomfortable for everybody -- and it leads to squinting and those loverly junkie-style pinpoint pupils everyone loves so much. Sure, you can fix 'em in post, but why? The pupil size alone makes flash worthwhile for portraiture -- people come off looking a lot friendlier and more approachable with larger pupils.
Flash also lets you work with movement, whether that's to give life to hair or clothing or to capture the briefest expressions. You can do that with continuous lighting as well, but it either means cranking the levels up to solar surface brightness or dealing with noise in post (or grain, if you're shooting film). That depends on your shooting style as well, I suppose, but most of what I shot was at around f/5.6 or f/8 and tightly framed -- you don't need to be at f/1.2 to get a DoF that has the subject in focus with little or no background detail if the subject/bg separation is enough to light the background separately. (A fast lens, though, does make critical focus a lot easier to achieve provided that the lens doesn't shift focus.)
Studio flash is more expensive at the entry level than continuous lighting, but it doesn't have to be outrageously so. There are a number of well-respected "off" brands (the only thing "off" about them is that they tend to be direct sellers rather than selling through retail outlets), like Paul C. Buff's AlienBees and White Lightning lines, as well as entry-level units from the "names", like Elinchrom's DLite series, that will let you in the game at about the price of a decent zoom lens. They're often cheaper than equivalent "name brand" continuous lighting kits. The only drawback I know of is that it's really hard to double them up for video use (although if the modelling lights are bright enough...).
There is another common division, you list hot lights and strobes. But there are at least two major types of strobes: Studio strobes (typically powered by battery packs or mains) and speedlights (small battery powered strobes).
There are many professional photographers who use and prefer speedlights (David Hobby, Joe McNally, Syl Arena). Check out their sites for insight.
I use speedlights, three LP160s and an ancient Vivitar 285. I like their small size and low prices. They are surprisingly flexible.
I may have one or two PB Einsteins on my future, but I'll get another LP160 years before that.
I think that speedlights can do the work for less money, but some folks think that big monoblocks say "professional" in ways that are important
Overall light output vs rate of energy usage / heat output.
There's a reason hot lights are called "hot"; they put out a lot of heat per unit of light, especially compared to strobes. And heat doesn't do anyone any good. That's why strobes are more often preferred for still photography, and hot lights are more often used for video (where strobes aren't an option).
Another consideration is the color of the light. While monolights and speedlights are 5500 to 8000K and appear very white, almost any domestic lighting will produce light between 2500 and 5000K which appears as a yellow or orange tone in the image.
LED lighting has come a long way recently with many consumer products available to help in the studio. For example there are 500W equivalent work-lights, some supplied with stands that are inexpensive and useful. If you dig around there are also high power screw-in LED bulbs, e.g. Savage 30W and 50W and fittings (e.g. Gary Wong) to mount on a light stand and hold an umbrella. These more modern LED lamps use high efficiency chips with a color temperature around 5500K.
If you are interested in something more exotic, there are studio LED systems that allow color adjustment by controlling the red, green and blue components. LED studio lamps may also have the ability to accept gels and other modifiers.
Continuous light is dim at photographic shutter speeds. For still life / tabletop work, where you can use a one second shutter speed without issue, continuous offers the advantage that you can see it (to plan it) and the camera can meter it. But for portraits, you will always be at higher ISO, lower shutter speed, and wider apertures than you would like. Sort of a constant struggle.
For that reason, flash is the popular way for portraits (subjects that might move). Flash easily allows ISO 100, f/8 at 1/200 second, where with continuous, you probably pray that ISO 800, f/2.8 at 1/30 second might be good enough. So in practice, there are very good odds that with continuous, you will either convert to flash soon, or give it up soon. Flash is used differently, so like anything else, there's a thing or two to learn. You have to take a test shot to see the result, and you will need a meter to set the levels of each light (to know what they are doing). However, you can simplify the setup with the meter, to then get what you expect (can repeat it closely next time).
Some samples of "continuous vs flash power" at http://www.scantips.com/lights/flashbasics2a.html