Although it’s an important question, few clients ever ask how bright their new lighting will be. In the hectic job of revamping a studio, such technicalities are usually left up to whoever’s doing the lighting. But because the answer will impact several systems down the line, choosing the right intensity needs to be based on your studio’s particular needs and not randomly picked. Here’s why.

Lighting will affect everything seen in the studio. This broad-ranging impact is why I suggest going through a process to discover exactly how much light is appropriate for the project. Rather than pulling a number out of a hat, I try to find the “Goldilocks” level that’s “Not too bright. Not too dark. Just right!”

Back in the early 1970s, cameras needed a whopping 300 fc (foot-candles) to produce decent pictures. That was bright enough to make you squint, rather than smile for the camera. Over the years, cameras have improved, and lighting levels have dropped a lot. Today, studio levels are a comfortable 45–65 fc. But there’s more to the task than simply picking a number in that range.

Camera Sensitivity Determines Light Intensity
Getting beautiful images requires more than just a correct exposure. Skilled photographers, cinematographers and videographers use a variety of camera techniques in crafting their images. Unless you happen to be a cinematographer as well as a lighting designer, you might not appreciate how much lighting affects the camera image. One particular camera adjustment that’s directly linked with light levels is the aperture (or iris). As we’ll see, this affects more than just the exposure.

In television, we want the viewer’s attention on the stories and the people telling them. By controlling which part of the shot is in sharp focus we direct the viewer’s eye to what’s important on the screen. By design we can control that sharp focus through manipulation of the “depth of field.”

Our sense of depth is possible because we have two eyes with overlapping fields of view. Cameras lack this type of binocular vision, called stereopsis, because they only “see” through a single lens. In the absence of stereopsis, a camera can still indicate depth by providing other visual cues for dimension. Depth of field is one such cue; by alternating a sharply focused zone against softer focused areas, our brain subconsciously builds a three-dimensional understanding of the pictured space.

So, how do we create this sense of depth by selecting the right light intensity? The lens adjustment that affects depth of field, as well as regulating how much light reaches the camera’s sensor, is the iris.

Bear with me while I cover what may be familiar ground to you. The iris (or aperture) regulates the light in increments called f-stops. The size of this aperture affects the depth of field through its impact on focus. Without delving into how the “circle of confusion” impacts focus, let’s just note that the smaller the iris opening (higher number f-stop), the greater the depth of field. The lower the f-stop number, the shallower the depth of field.

The photographer Ansel Adams famously used f/64 to get everything in sharp focus for his iconic images of the American West. While that infinite depth of field was appropriate for his scenic images, we don’t want that for our studio shows.

In newscasts or interviews, we want the visual emphasis on the talent. Towards that end, we focus attention on them with a bust shot that’s in sharper focus than the background. That selective focus is achieved by choosing an f-stop that simultaneously provides the depth of field we want and the right amount of light for a good exposure. But which f-stop is that?

My personal choice for the “Goldilocks” f-stop sits between f/2.8 and f/4. That aperture provides an adequate depth of field to keep the anchors in focus, and just the right amount of background softening to suggest some separating distance. That “f/2.8–f/4 split” is the sweet spot where I start the process of determining how much light I need to use.

Light To the F-Stop for Desired Depth of Field
To find out how much light you need for your cameras, frame a shot of the chip chart (with teleprompter to account for the light loss from the mirror) from roughly 8 feet away to approximate the “normal” anchor-to-camera distance.

White-balance with the clear camera filter at whatever color temperature lighting you’re using in your studio. Set the iris to the mark between f/2.8 and f/4. Then, adjust the chip-chart light brightness until the chips fall into their proper levels on a waveform monitor.

Once that’s done, take a light meter reading of the chart intensity from in front of the chart (sphere diffuser, pointing back to the camera lens). Whatever intensity reading you get is the value to use for your lighting positions. For most studio cameras today, it will probably be somewhere between 45 fc and 65 fc.

If the number you get is lower than 45 fc, you may need to make a modification to boost that number higher. This is especially true if your set incorporates video displays, which perform poorly at very low brightness levels. The solution is to rerun the process with the cameras set at a –3 db “gain,” which will nudge the required light level higher.

That’s my process for deciding what the “right” light level is. Neither the intensity nor the f-stop should be arbitrary or accidental in crafting an image. That’s why this process is driven by the choice of f-stop, which is, in turn, based on the depth of field we want.

The “f/2.8–f/4 split” is a subjective choice that I think looks best for most news sets. Your criteria may be different, based on how much (or little) depth of field you want. The process will run the same regardless of which f-stop you choose. The point is to choose by design, rather than haphazardly.

In my day (excuse me while I stoke up my pipe), the principle measurement of photometrics was the footcandle. The humble footcandle is the measurement of the light of 1 candle on a 1 foot square area 1 foot away from the flame. Footcandles also had their counterpart, footlamberts, measuring light reflecting off of a subject. Light meters still operate in footcandles as do most photometrics reported by manufacturers to this date. The footcandle is the equivalent to 1 candela over 1 square foot.

SWITCHING TO METRICS
Of course, this is an English system of measurement—one that only a small handful of countries in the world today actually use. Hey kids, remember talking about the metric system in math class and being told that the United States would be switching over to metrics soon? Perhaps soon is really relative to the existence of time as we know it, rather than our individual lifetimes.

In any case, the metric measurement of footcandle is the lux, which is 1 lumen (let’s call the lumen and the candela “kissing cousins,” if you will) over a 1 square meter area. Pretty much exactly the same thing, except that 1 square meter is 10.74 square feet. So 1 lux = 10.74 footcandles. You with me so far?

OK, great. This is the professional way of discussing a luminary’s intensity of light over a given distance. What, however, if we just want to discuss the brightness of a source without regard to distance of light traveled?

Packaging requirements are moving away from wattage to denote lumens.

For more than one hundred years, this was commonly done by discussing the wattage of a given light source. As most incandescent light sources of similar wattage are close to each other in given output, this has become a standard. How bright of a source do you need? 100 watts? 200? 1,000? Professionals and laypersons alike had a frame of reference for these numbers.

My mother understands how bright a 60W bulb will be when she needs to replace a burned-out bulb in her living room. She knows that a 100 watt bulb will be too bright for her and a 40 watt bulb will be too dim.

We’ve utilized this same frame of reference for decades in the motion picture business—since the rise of the tungsten fixture (over carbon arcs). We order lighting based on wattage: six 1,000 watt fixtures, four 2,000 watt fixtures, 10 650 watt fixtures.

Yet wattage has no direct bearing on the brightness of a fixture, especially not in modern-day technology. Wattage only describes the amount of power necessary (the product of amperage and voltage) to power a luminary. As the technology of lighting continues to evolve, new advancements in lighting—HMIs, fluorescent, LED and plasma lighting fixtures—have substantially lower wattage ratings for substantially higher light outputs than the equivalent wattage in tungsten bulbs.

KNOWING THE DIFFERENCE
Generally speaking, lighting professionals simply, intuitively, know the difference. We understand that a 2,000 watt tungsten fixture would be substantially less bright than a 1,200 watt HMI fixture. Beyond newbies coming in on their first week of the job, this is common knowledge. However, how does 100 watts of LED compare to 100 watts of tungsten-halogen compare to 100 watts of HMI compare to 100 watts of fluorescent to 100 watts of plasma? Ask any gaffer, chief lighting technician or lighting designer and you’re likely to get a shrug. Try to ask a consumer what the difference is between a 100 watt CFL, 100 watt tungsten lightbulb and a 100 watt LED and you’re likely to get the deer-in-headlights stare.

As the different luminaries have different electrical requirements and efficiencies, we’re slowly doing away with the old frame of reference. This is starting in the consumer world where packaging requirements are moving away from wattage to denote lumens. How many lumens does a light source emit? In actuality, not just for typical consumers, but for all of us, this is a much more universal and accurate descriptor of a fixture’s brightness value, and where we should also follow with our own manufacturers reporting.

Table 1: Comparison of various lumen outputs and the relative wattage equivalents of consumer incandescent bulbs, CFLs and LEDs

The lumen is a consistent form of intensity measurement, regardless of the source or power consumption, (Table 1).

Obviously, when we can get roughly the same lighting intensity from a 25 watt LED as we can a 150 watt tungsten bulb, the wattage can no longer be considered a universal factor in determining a luminary’s intensity.

I’d like to see a lot more manufacturers of professional lighting equipment start to list the lumen output on their fixtures along with the typical photometric information. Hopefully many will follow suit in the next few years.

Jay Holben is the author of the book “A Shot in the Dark: A Creative DIY Guide to Digital Video Lighting on (Almost) No Budget.”