Does removing modeling light = increase from main tube?

After observing reviews where others use model lamps, I questioned whether the model lamps reduce output from the main tube. Not a lot, but a little.

Some light must go straight forward and some to the side. But it seems that the flash tube must omit some light from the edge facing the model light. The model lights look frosted and seem like they could block some of that light from crossing the center toward the other edge of the modifier. Has anyone ever done an exposure test by comparing shots or recording with a light meter to compare output of the strobe with and without modeling bulb?

mdvaden wrote in post #19314602
After observing reviews where others use model lamps, I questioned whether the model lamps reduce output from the main tube. Not a lot, but a little.

Some light must go straight forward and some to the side. But it seems that the flash tube must omit some light from the edge facing the model light. The model lights look frosted and seem like they could block some of that light from crossing the center toward the other edge of the modifier. Has anyone ever done an exposure test by comparing shots or recording with a light meter to compare output of the strobe with and without modeling bulb?

Not tested but seems quite immaterial. The flash tube itself would block the other side using the same theory.

Even if 100% impacted it’s out of frame and you’d likely be using a modifier anyway.

ImageMaker... wrote in post #19314606
Not tested but seems quite immaterial. The flash tube itself would block the other side using the same theory.

Even if 100% impacted it’s out of frame and you’d likely be using a modifier anyway.

Not in the same way, since the model light protrudes much further.

The blue represents the path of light being blocked by the model lamp tube --- at least that's what I question.

Or ... does the surface of the model lamp still reflect the light outward.

mdvaden wrote in post #19315131
Not in the same way, since the model light protrudes much further.

The blue represents the path of light being blocked by the model lamp tube --- at least that's what I question.

Or ... does the surface of the model lamp still reflect the light outward.

Hosted photo: posted by mdvaden in
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forum: Flash and Studio Lighting

Remove the modeling light. Take a picture.
Put back the modeling light. Take the SAME picture.

No difference.

…and it just doesn’t matter anyway.

This is one of those silly theoretical debates that make people who simply use their gear shake their heads. As mentioned above, the test is simple and if there was any (likely infinitesimal) difference it would differ for each model an brand of light. The presence of the modeling light bulb wouldn't reduce the output of the tube, at most it might redirect that power into a slightly different shape (light pattern) that would be mitigated greatly by any modifier or accessory reflector being used. If all that did make a difference it would likely be difficult to actually measure as it's probably less than 1/10 of a stop. This is one of those times when you should stop worrying about it and just use your gear.

The modelling light bulb is mostly transparent (glass) and only a little bit obscuring to light striking the solid portions (filament).
If you held the modelling light bulb in front of a flashlight beam, you likely would not notice much of a change in the intensity of the beam on the wall, as a fraction of the total light projected. That is an example (a very imperfect one, as your fingers would also be in the way as well!) of what you do to the light from a xenon flash tube which is emitted from many different angles compared to the location of the modelling light bulb. Given the very large (relative to the filament) area of the light area of the xenon tube, what is obscured by the filament is such a tiny percentage of the total area of the xenon light projected as to be miniscule effect on exposure at the subject...you probably hurt light output more by having the reflector badly fingerprinted instead of shiny.

Wilt wrote in post #19315299
The modelling light bulb is mostly transparent (glass) and only a little bit obscuring to light striking the solid portions (filament).
If you held the modelling light bulb in front of a flashlight beam, you likely would not notice much of a change in the intensity of the beam on the wall, as a fraction of the total light projected. That is an example (a very imperfect one, as your fingers would also be in the way as well!) of what you do to the light from a xenon flash tube which is emitted from many different angles compared to the location of the modelling light bulb. Given the very large (relative to the filament) area of the light area of the xenon tube, what is obscured by the filament is such a tiny percentage of the total area of the xenon light projected as to be miniscule effect on exposure at the subject...you probably hurt light output more by having the reflector badly fingerprinted instead of shiny.

From what you wrote, then at worst a modeling bulb may act as a mild diffuser with near nil loss of light.

mdvaden wrote in post #19315429
From what you wrote, then at worst a modeling bulb may act as a mild diffuser with near nil loss of light.

• Not a 'diffuser' in the sense of enlarging the apparent size of the light source.
  
• Maybe a 'diffuser' in the sense of making the light be a tiny bit less collimated (e.g. what the front panel of a softbox does), but what little 'diffusion' it does is so little as to have virtually no observable effect on the directionality of the light cast from that source.
  
• And certainly 'Nil loss of light'