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Why Strobes Over Continuous Light

joshua hudson , Jun 02, 2006; 09:35 a.m.

Why Strobes Over Continuous Light By Joshua Hudson, www.dragonflydigitalmedia.com

You are on a budget and you want to make your own studio lights. Shop online and you will find that lighting is not cheap, but where do you start. Are the Watts on a light bulb the same as the Watt Seconds on a Studio Strobe? Here is a little primer on what the average "photo Joe" needs to know about light.

First off, watts are not a measure of light. Electrical power is measured in watts. A household light bulb is measure not by the amount of light produced but by the very economics driven "electrical power used." So we can never really measure light by power consumption. This is why you find that a fluorescent bulb, which is much more efficient, can create more light at 46 watts than a 500 watt halogen or incandescent light. And because it is more efficient in its use of wattage, it produces much less heat.

The only true measures of light are Guide Numbers, Lumens and LUX.

A LUMEN is a unit of measurement of light. It measures light much the same way we do a foot/candle (or Lux). Remember, a foot-candle is how bright the light is one foot away from the source. A lumen is a way of measuring how much light gets to what you want to light! A LUMEN is equal to one foot-candle falling on one square foot of area.

Candlepower is a rating of light output at the source, using English measurements. Foot-candles are a measurement of light at an illuminated object. Lumens are a metric equivalent to foot-candles in that they are measured at an object you want to illuminate

You can find the lumens of any continuous bulb usually on the packaging. It takes a lot of lumens to light up a set. Human eyes are much more sensitive to light than cameras and what seems incredibly bright to use is barely significant to most of our photos. Bare minimum portrait lights should start at 10,000 lumens. I would not even try to do a portrait sitting without my main light being at least 20,000 lumens. With unscientific research, I estimated my test with continuous lighting to make a 20,000-lumen light about a 150 watt- second strobe.

So watt seconds can't possibly be a unit of light measurement either, huh? Yup! Exactamundo! Watt Seconds (ws) are a unit of energy, commonly used in advertising for AC-powered studio flash units. It is not, however, a unit of actual light output, so comparing the watt-second ratings of different flash units is not usually useful. This is why you get people like Paul Huff giving actual watt-seconds vs true watt seconds. True watt seconds is a watt second by definition, while actual watt seconds are white lightning�s way of saying their flashes are brighter because they use more efficient capacitors. I totally believe that Paul is telling the truth that his lights are brighter than other strobes rated at the same ws but there is no such thing as an actual watt second. Nor can you measure lumens by watts seconds.

What you CAN do with strobes is measure the light with a Guide Number (GN). The GN is used in flash calculations to determine the appropriate aperture required to cover a certain distance or vice-versa. To find the aperture (f stop number) required to take a photo of a subject you divide the flash unit�s guide number by the distance to the subject. To find the maximum distance that can be reasonably illuminated using the current aperture setting you divide the guide number by the f stop number. In each case it�s the distance from the flash to the subject that�s important, not the distance from the camera to the subject. These two distances may be the same with on-camera flash, but not with off- camera flash or when using bounce flash.

f-stop number = GN / distance distance = GN / f-stop number

Note that you are not getting a reading in lumens, but a way of figuring exposure. So then how are you going to determine if your continuous light is going to be equal to your flash? Simple. Look at your exposure on your camera and compare. You will find that a 1000 watt halogen will put out just under 10,000 lumens and gets you about 1/60th, f/2.8 on ISO 200 at 5 feet away.. That is a really slow shutter speed and very wide f/stop for a studio light. Even the cheapest $30 Vivitar 283 is going to give you a GN of 85-- which means at 5 feet you are going to get an f/stop of f/16 at the shutter sync speed of your camera on ISO 200. That is an average of five stops difference.

But don't let that discourage you from making a good set of home bees or continuous lighting. There are some great reasons to have continuous light. You get a great idea of what your photos will look like, unlike strobes. Continuous lighting is great for products as well, since they do not move and you can adjust your f/stop for slower shutter speeds. And if you are a fan of very small apertures, you can get some great shallow depth of field shots.

Most of all, you can still shoot continuous because it is fun. Home Bees are simple to make, cheap and a really fun time for a photographer on a rainy day!


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Steve Levine , Jun 02, 2006; 09:56 a.m.

What you don't mention is that in order to achieve say F8, with hard lights. You can burn down your house.

Eric Friedemann , Jun 02, 2006; 10:21 a.m.

There is nothing morally wrong with continuous lights; its just that continuous lights are:

1. Hot, as Steve noted. They make portrait subjects sweat.

2. Hard on a portrait subjects' eyes, making people squint after a little while.

Brooks Short - Tampa, Florida , Jun 02, 2006; 10:39 a.m.

" There are some great reasons to have continuous light. You get a great idea of what your photos will look like, unlike strobes."

Once again the myth of only hot lights providing WYSIWYG lighting rears it's hot, sweaty head.

If you try to use portable camera flashes that don't have modeling lights or cheap studio strobes with dim 100 watt model lamps this blanket statement is correct. But those are almost as poor a choice for studio lighting as hot lights.

If you use studio strobes with 250 watt or higher modeling lights you can see exactly what your lighting will look like and you can avoid all of the disadvantages of using hot lights.

Garry Edwards has written a definitive article on different lighting equipment which is archived in the Administration section of this Lighting Forum. You might want to check it out.

Nick Zentena , Jun 02, 2006; 11:59 a.m.

I think I'd rather use flash powder. This new fangled continous light won't last.

John Murphy , Jun 02, 2006; 12:30 p.m.


Before I had come across this forum, I had bought into the Hot-Lights-Are-Good-For-Beginners idea. I quickly realized that they are a nightmare to use for portraits of kids, and that they simply cannot provide adequate power for large format portraits of children.

Interestingly, by my calculations, hot lights aren't really much cheaper than strobes. Sure, the light itself is cheaper, but the light modifiers (e.g., softboxes) tend to be costlier.

Lastly, ultraviolet light injury to the eyes is a bigger concern with hotlights than with strobes, because of the longer duration of exposure to the damaging rays.

Terence Heuston , Jun 02, 2006; 01:49 p.m.

I just wanted to offer an alternate perspective. In certain LIMITED (don't flame me) situations I prefer continuous lights. When I'm photographing a headshot in studio I often prefer kino-flos (they are high frequency flourescents that run cool) over my profoto 7a 1200 pack with 7 foot octa. I am able to shoot F4 @ 125 which I like for the limited d.o.f. Often my profoto pack at the lowest power setting cannot keep pace with my shooting style. When a person has a true genuine laugh or smile it changes rapidly. It is not unusual for me to shoot 3 or 4 fps over the course of a laugh (I don't do this for the entire shoot - just when capturing a truly alive and real moment). My pack can't keep up with that pace. On the downside kinos are really heavy compared to flash heads and require heavy shotbags on heavy stands, they offer only one kind of diffused light which is very limiting at a ridiculously low level compared to strobes. Also, if your subject moves too much they'll be out of focus. The upside is they are continuous which does make seeing the shot easier for me, run cool, give off a very flattering soft light for portraits, I prefer the look of the kino catch lights in the eyes over the big saucers of a softbox, some subjects find strobes disconcerting and become tense compared to continuous, and I get to use them on video and film shoots because they're continuous. Lastly, I've read about really successful commercial photographers that use them for table top photos because they find it easier to see the shot using continuous lights.

Brooks Short - Tampa, Florida , Jun 02, 2006; 07:32 p.m.


I know...I know. What else can I say?

Stephen H , Jun 02, 2006; 11:25 p.m.

"I think I'd rather use flash powder. This new fangled continous light won't last."

Flipping channels the other day, I ran across a scene where they were shooting with flash powder. Poof! Big puff of smoke! Only...it was broad daylight, sunny even.

Nick Zentena , Jun 03, 2006; 07:34 a.m.

Plenty of fine photos have been made with flash powder. Why change?

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