I’m trying to get some working numbers for illumination levels with fluorescents, which I don’t have but may purchase. Perhaps one of you with plenty of experience on set can help.

Let’s start with a 110W (2 55W tubes) unit, such as made by Cool Lights or Lowel. If I place one of these 5-6 feet from a single seated subject, assuming no significant ambient light or fill bounced back from surround surfaces, what kind of incident f/ stop am I likely to have with, say, a decent, mid-range HD camera, ($3-4 grand)?

Yes, I realize that there are a number of variables in there; but as with any luminaire, camera type, etc., there’s a ballpark region with upper and lower general limits, and that’s all I’m looking for at the moment.

Cool Lights, for instance, gives a tungsten:flo efficiency ratio rule-of-thumb of 4:1, i.e., 100 watts of flo approximates 400 of tungsten. Again, I’m aware of the variables, lamp configuration, square law differences with soft lighting, etc. But here’s a typical situation, slightly modified from that with the raw light above. Let’s say I have in my kit a Lowel Omni w/a standard reflector and 500W lamp, a 110W 24” 2-tube flo, and a 200W compact flo. Let’s say I set up the Omni and place it 2’ behind a 4x4 ft. diffusion panel (e.g., ripstop nylon) which is 5 ft from my subject, about 45 degrees. I’m guesstimating now, but let’s say that without any added gain, in an environment such as cited above, I get an aperture of f/4. My next guess, is that doing the same with the tube flo would drop the level down 1 1/2 to 2 stops, and that the compact flo might give me something in between.

I’d appreciate any informed comment from experienced folks.

Philip:

This is an exercise in futility unless you quantify more parameters. What shutter speed, what ISO is the camera rated at, what is the ambient light level in the room?

Fluoros and LEDs to a point have quicker falloff than tungsten lights so I would not key an interview from 6 feet with one, more like 2-3 feet would keep the light nice and soft. A $3-4 grand HD camcorder is very low end, a mid range HD camera is more like $15 to $20k, but that is semantics I guess. The difference being though is that all cheap HD camcorders with the exception of the Sony EX1/EX3 use 1/3" imagers or smaller unless you are counting the Canon 5D MKII. Mid range HD camcorder use 2/3" imagers, which are much more light sensitive than small imagers. See what I mean, you need an ISO rating on the camera for any calculations to be meaningful.

I have to Kino Diva 200 equivalents (dual 55 watt biax with Kino 5500k tubes) and I usually will use the key at two to three feet away from a seated talent, I will use the second light as a fill source, perhaps 3-4 away on the opposite side although I often can unplug one of the tubes so that I am only using a single tube as my fill source. Using the DVX100A, which I rate at ISO 640, at 24p with a 180 degree shutter, I am usually at around a 3.5/2.8 split. But when I use the HVX-200, in the same setup, I am wide open. With the HPX170, which I rate at ISO 500 at 180 degree shutter, I am at a 2.8 usually. It depends on the camera, frame rate, shutter speed, ambient light, etc.

Usually with small cameras, you want the lens close to wide open anyway to give you the shallowest DOF for interviews anyway, unless you are shooting greenscreen or black limbo BG.

Dan

Dan, my thanks. Despite the missing variables, what you provided already gives me starting point.

What I don't know about video camera specs could fill a large book, but I'm aware of the smaller sensors' sensitivity limitations; that's all the group I'm assisting has to work with. I don't know the specs of their camera yet, and am just in the beginning of the process of helping them scope out the best tools for lighting for their purposes (see my recent post on office studio space in the Home Away from Home forum). I am testing the water in this post here, to see if someone who knows better than replied, "Are you out of your mind?! You'd be lucky to get f/1.2 with twice the wattage from the flos," or some other indication that I am way off-base. From what you indicate, I'm in the ballpark I expected to be in, and now need to do some preliminary tests.

Anyone else?

The readings I just took off my CL-255PMD are 2300, 910 and 380 lux at 2, 4 and 6 feet respectively. As Dan said, obviously this type of fixture is most effective in the first 3 feet or so because of the drop off of soft light.