Flash output question

[Two23]

That's like saying that you just can't tell how much light a 100W lightbulb will produce.

Ah, but is the glass the bulb is made from colored? From how far away are you measuring the light the bulb puts out? Is the bulb just hanging down by itself from a long cord, or is there a reflector of some kind behind it? Is the bulb covered over by a lampshade? How opaque is that lampshade? Is the bulb being used in a small room with white walls, or is it a single bulb in a very large hall with dark wood paneling?


Kent in SD

[Leigh]

That's like saying that you just can't tell how much light a 100W lightbulb will produce.

That's correct. You can't.
If you know the other characteristics of the bulb you can estimate fairly accurately.

Flash systems are more complex.

- Leigh

[C. D. Keth]

Ah, but is the glass the bulb is made from colored? From how far away are you measuring the light the bulb puts out? Is the bulb just hanging down by itself from a long cord, or is there a reflector of some kind behind it? Is the bulb covered over by a lampshade? How opaque is that lampshade? Is the bulb being used in a small room with white walls, or is it a single bulb in a very large hall with dark wood paneling?


Kent in SD

All those other things don't matter for what wattage (and watt-seconds) is for in that application. It's for ballparking your needs. How many heads and of what type. Everybody knows what a 100W lightbulb looks like. Do you see CFLs labeled with "produces 1700 lumens!"? No. An experienced photographer can ballpark his needs based on the watt seconds rating and the rest simply doesn't matter unless you are prelighting an entire set on paper and it must be right. Unless you are doing that, the photometrics are for scientists and marketing people to argue about and for overly anal photographers to obsess over. If you're interested in lighting something or somebody and not interested in every little intricacy of the equipment, watt-seconds is enough to get you there quickly and simply.

That's correct. You can't.
If you know the other characteristics of the bulb you can estimate fairly accurately.

Flash systems are more complex.

- Leigh

They are more complex but all that simply doesn't matter. Knowing the watt-second rating, I can light 90% of the way without ever turning the power on or getting a meter out. I'm not bragging, any photographer should be able to do it if he's paying attention. That last 10% is fine tuning with a meter anyway so you still don't need to know any of the photometrics.


It's really a question of whether one actually wants to use lighting equipment or obsess over it.

[Leigh]

Anybody can do 90% of a job.

- Leigh

[Jody_S]

Quote Originally Posted by Christopher D. Keth View Post
That's like saying that you just can't tell how much light a 100W lightbulb will produce.


That's correct. You can't.
If you know the other characteristics of the bulb you can estimate fairly accurately.

Flash systems are more complex.

- Leigh



- Leigh

Yes, you can, to a far greater degree of accuracy than anything photography-related ever requires, simply by measuring the power consumption of the bulb when lit. What you might not be able to do, with a simple calculation, is to say how much of that output falls within visible range. The main difficulty will be determining where the electrical infrastructure stops and where the 'light bulb' begins, and of course procuring a power meter of sufficient accuracy (Fluke's published specs are/were* +/- 10%).

For visible light, or 'useful' light, you will need the published age/output tables from the main manufacturers, of which I have some volumes dating to the 50s. Photography flash systems don't normally come with that sort of data, certainly not to the degree that electrical engineers have documented the life span of commercial lighting systems. I guess they all assume that anyone doing critical work will simply buy new flash systems whenever they feel their photos are 'off'.


*Last time I purchased a defective meter and attempted to return it, confirmed when I looked it up for a physics class lab.

[Leigh]

What you might not be able to do, with a simple calculation, is to say how much of that output falls within visible range.

Well, Jody,

Since we are all photographers, I thought it was obvious that my comments related to VISIBLE light output.

The post to which I responded said how much LIGHT the bulb would produce.

Perhaps I over-estimated the intelligence of the audience.

- Leigh

[Jody_S]

Well, Jody,

Since we are all photographers, I thought it was obvious that my comments related to VISIBLE light output.

The post to which I responded said how much LIGHT the bulb would produce.

Perhaps I over-estimated the intelligence of the audience.

- Leigh

The remainder of my comment addressed the difficulties faced by photographers. Simply put: flash manufacturers do not publish the necessary data, not that it's all that difficult to measure and graph, should you so choose (and have on hand enough examples of a given flash to reach statistical relevance). But you need to know such things as how much dust is present in a given environment, and your result will be a series of graphs that you will have to match against graphs of film spectrum sensitivity. A simple engineering calculator will then pop out all the figures you need, for statistical probabilities. You still have the risk of using a particular flash that falls outside your calculated probability range. This might not be a trivial exercise if you want to consistently produce photos with, say, faithful rendering of skin tones.

[Frank Petronio]

In practical terms, you set up the two competing flash units in a likely scenario, perhaps a portrait or still-life set up and use them. They can vary 2-3 stops depending on the types of light modifiers, design, and environment. Or you may decide you prefer one for cost or usability factors.

Using continuous light for still-life or architecture simply requires longer exposures ~ often lower power units are more practical and less expensive.

Using continuous light for portraits and action is kind of foolish, I do it often but they're usually unusual circumstances and wide-open ~ I wouldn't advise it for normal, traditional large-format images.

[Sevo]

That's correct. You can't.
If you know the other characteristics of the bulb you can estimate fairly accurately.

Flash systems are more complex.

As a matter of fact, they are more simple, if any - the number of actual tube component manufacturers is tiny, and there haven't been any fundamentally different tubes being made throughout the past sixty years or so. By comparison, there have been hundreds of lamp systems with different efficiency and spectral characteristics for continuous light lamps, and dozens of them are currently marketed on a broad scale. Any average house will contain more lamps with mutually incompatible filtering/white balance requirements and wattage efficiency than you could have bought across the entire history of photographic flash systems...

In my experience, Ws ratings for both flash heads and generators are close enough that there are only very minor issues mixing and matching across manufacturers (which can generally be dealt with by applying some maker-specific constant within one stop above or below average). Even halogen came in two (3200 and 3400K with more than a stop brightness difference) photographic variations, plus even more for household use.

[Robert Budding]

Well, Jody,

Since we are all photographers, I thought it was obvious that my comments related to VISIBLE light output.

The post to which I responded said how much LIGHT the bulb would produce.

Perhaps I over-estimated the intelligence of the audience.

- Leigh

If you stopped to think about Jody's comment, instead of trumpeting your vastly superior intellect, then you'd realize that non-visible light could matter. It is waste because it consumes power, and it isn't useful to photographers. Of course you could still compare power for various lights if they had similar efficiency in generating usable light. But that wouldn't work well if, for example, one manufacturer's light put out a great deal of UV light.