Flash output question

[Jody_S]

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.

I'm researching this because I recently obtained a lot of infrared film. Turns out there's a huge variation between flash manufacturers in the amount of infrared they put out. For portable flashes, it seems Metz (45CT and 60CT series) is the best for infrared, or the most wasteful if you're shooting something else. I have both, if I put an infrared filter over the flash instead of the lens, I should be able to photograph at night completely incognito. Of course, calculating exposure is problematic....

[Sevo]

I'm researching this because I recently obtained a lot of infrared film. Turns out there's a huge variation between flash manufacturers in the amount of infrared they put out. For portable flashes, it seems Metz (45CT and 60CT series) is the best for infrared, or the most wasteful if you're shooting something else.

That is a matter of filtering rather than the discharge output - some flashes have UV/IR blocking filters, others block only UV (and some technical use tubes block nothing at all).

[Emmanuel BIGLER]

Hello all !

In those days where everybody has to save energy, good citizens concerned by the health of Our Planet should actually care for the efficiency of their flash units !

Norm Buchanan has mentioned capacitors used to store the energy in all electronic flash units.
To the best of my knowledge, the rating in terms of joules (= watts . seconds) refers to the actual electrostatic energy stored inside the capacitor, according to the good old formula found in physics textbooks
E =(1/2) C V^2

Hence, this energy in joules which is exceedingly easy to compute given the capacitance C and the maximum static charging voltage V, is eventually transformed through a certain efficiency / conversion factor into a large spectrum of visible and invisible photons. It is extremely difficult to properly set a clear and easy conversion factor between those electrostatic joules in input into either visible photometric units or energetic photometric units in output.

There is a similar situation in the rating of Hi-Fi loudspeakers. At least this was the situation in the last century when Hi-Fi systems were an object of fascination and social distinction
The rating was (and probably still is) in watts, but those watts refer to the maximum electrical energy absorbed by the loudspeaker at full power. The conversion factor into real acoustic power is so low that no vendor of HiFi loudspeakers could dare to tell the truth, i.e. that a 100W-rated loudspeaker delivers only a few "real acoustic" watts in air ...

The fact that flash rating is in joules and HiFi loudspeakers rating in watts is simply due to the fact that flash units operate in a single-stroke mode (or multiple, stroboscopic mode) whereas most of the times, loudspeakers operate in a steady-state of acoustic emission. But the problem of converting electrical energy into photometric energy or acoustic energy is similar, the efficiency in both cases is very low.

going off-topic : another field were fancy wattage was the standard, at least in France, was electrical tools (drills, saw, routers, ) for amateur use; the rating was based on absorbed electrical wattage and not at all on true mechanical power delivered on output. Only professional machine-tools have their electrical motor rated in terms of actual mechanical power, often in the past rated in horse power (CV in France) and now in real "mechanical kilowatts". It happens that the efficiency of a modern electrical motor is quite hight, say, 80% or even higher, so it does not really hurt to tell the truth in terms of mechanical output watts, unlike flash units or HiFi loudspeakers ...

Electronic flash units designed for amateur use are rated according to a guide number, in Europe we use a metric guide number, I assume that this definition of the guide number may vary in some other parts of the (e.g.: non-metric) world
However for professional studio use, the guide number is more or less irrelevant since nobody can use the guide number when you carefully build a nice flash lighting with many separated studio flash units with all kinds of diffusers: the guide number is useful only for a small portable flash unit located at the same place as the camera itself, may be the worst-case of all kinds of flash lighting ...

[Bob Salomon]

"some technical use tubes block nothing at all"

Including many low cost amateur and professional flash units including monolights and power pack units. It is one area that they can reduce cost in at the cost of the results.

[Sevo]

"some technical use tubes block nothing at all"

Including many low cost amateur and professional flash units including monolights and power pack units. It is one area that they can reduce cost in at the cost of the results.

That must be a fairly new development, and I'm surprised any vendor can get away with it - even with digital more UV blind than film you'd still have issues with fluorescent colours in the subject creating partial, uncorrectable colour shifts. When I last was shopping for flashes (some seven or eight years ago) even the most pedestrian studio flashes still came with a (UV blocking) "gold" coated tube by default. Some makers (and even more third party replacement tube vendors, whose offers extend to non-photographic applications) offer a choice of clear or "gold" tubes as a replacement, and I've once seen a lazy/stupid technician from a rental place with a extensive stage and club section put a clear tube in a studio flash, but so far I've never seen them in a new-in-box flash...

IR is a different matter - blocking IR is achieved with a extra cover glass which has to be protected from thermal strain, additionally complicating the construction of the head, so IR filtering is a characteristic of the more expensive, up-market devices.

[Leigh]

... you'd realize that non-visible light could matter. It is waste because it consumes power, and it isn't useful to photographers.

That's correct. In fact, it's exactly what I said:
"...I thought it was obvious that my comments related to VISIBLE light output."

There are numerous sources of loss/waste in a studio strobe system.
All of it subtracts from the theoretical power available at the head, which produces visible light (or IR if you wish).

- Leigh

[Bob Salomon]

That must be a fairly new development, and I'm surprised any vendor can get away with it - even with digital more UV blind than film you'd still have issues with fluorescent colours in the subject creating partial, uncorrectable colour shifts. When I last was shopping for flashes (some seven or eight years ago) even the most pedestrian studio flashes still came with a (UV blocking) "gold" coated tube by default. Some makers (and even more third party replacement tube vendors, whose offers extend to non-photographic applications) offer a choice of clear or "gold" tubes as a replacement, and I've once seen a lazy/stupid technician from a rental place with a extensive stage and club section put a clear tube in a studio flash, but so far I've never seen them in a new-in-box flash...

IR is a different matter - blocking IR is achieved with a extra cover glass which has to be protected from thermal strain, additionally complicating the construction of the head, so IR filtering is a characteristic of the more expensive, up-market devices.

No, this is old news. When Rollei Studion Flash came on the market in the early to mid 70's they were the first studio flash manufacturer to use UV coated tubes and Titanium dioxide painted reflectors.
Up till then there were many photographers who had problems with things changing color when photographed, especially a lot of fabrics and especially those with brighteners. The Rollei studio flash systems eliminated most of these problems and we even sold them in 1974 to the Kodak Research Studios. They used them to prove to photographers that the change of color with materials that they sent to Kodak for testing was not a result of the film but a problem with the flash.

Yes there were certain colors that the color film could not reproduce correctly and no flash or hot light could correctly reproduce. And we did learn after spending an entire day at the Jello factory that purple grape jello would not reproduce correctly (Jello shot an image of each batch as part of their QC procedure, we could only make this flavor photograph black).

But anyone who has shot a guy in a tux that comes out the wrong color or a brides shoes that were dyed or a mother-in-laws dress that comes out wrong or a group of bride's maids who have off color shoes or dresses has experienced non-UV corrected flash. It has been going on for a very long time.

[Sevo]

No, this is old news. When Rollei Studion Flash came on the market in the early to mid 70's they were the first studio flash manufacturer to use UV coated tubes and Titanium dioxide painted reflectors.

Ah, ok, that is somewhat further back in time than I was talking about - by the eighties, coating already was standard.