The following table shows lighting ratio
calculations for a hypothetical lighting example where the fill
light is set to a fixed strength (f4 as measured by the flash meter)
and the main light's strength is adjusted incrementally (f4,
f5.6, f8,f11 and f16). Keep in mind that each f-stop increase
in the light meter reading is equivalent to a doubling of the
||Fill Light Units
||Main Light Units
OTHER SOURCES OF SHADOW ILLUMINATION
When selecting your fill-light strength, you
may have to keep in mind several common factors that affect the
final density of your shadow areas. Some of these factors are:
- Stray Light - Small studios with
light-colored walls can reflect about a significant amount of
light and may require a reduction in fill-source strength.
Large dark spaces may require more fill.
- Clothing Choices - Light-toned
clothing can reflect a lot of light, reducing the amount of fill
- Lighting Modifiers - Large soft sources
create gradual shadow transitions and, depending on placement,
often wrap a sizeable portion of light into the shadow areas.
You may want to use less fill lighting with these sources.
Smaller, harder sources produce distinct shadow edges and wrap
little light into the shadow areas, often necessitating an
increase in fill lighting. Additionally, because of their
broad coverage, large sources often contribute more to stray
light than most smaller sources.
- Diffusion - All diffusion filters reduce
overall image contrast and bend some light from the highlights
into the shadows. Black-dot and black-netting diffusers,
which rely primarily on diffraction for diffusion, appear to
cause the least amount of shadow lightening. Other filter
types can have a significant affect on shadow density.
Main eight times strength of fill (9:1)
Main & fill equal strength (2:1)
Main twice strength of fill (3:1)
Main four times strength of fill(5:1)
The following images show the same scene shot
at various lighting ratios. All were created with an
on-axis fill light and a main light fitted with a 16" parabolic
reflector with barn doors. This particular main-light source
produces a fairly distinct shadow edge. If you use a larger
lighting modifier, such as an umbrella or softbox, expect your
shadow transitions to be more gradual for similar ratios.
These images were produced at approximately the same contrast/gamma;
your images shot at the same ratios may exhibit more or less
Ratio = Fill + Main
: Fill only
Diagram f.1 shows one of the most common
implementations. A large, soft source is placed behind the
camera on the camera-to-subject axis. This approach creates a
flat fill that illuminates most all of what is visible to the
camera. Diagram f.2 depicts another frequently used approach,
with the fill and main lights on opposite sides of the camera.
In this implementation, the fill light is often placed closer to the
camera-to-subject axis than the main source. Form fill, shown
in diagram f.3, is a bit more complicated to use. The
form fill generally faces squarely into the subjects face and lights
the front ( mask ) of the face. As the face moves, the form
fill follows it. Another way of looking at it is that the
subject's nose always points at the form fill. The form
fill is often used in conjunction with a main/accent light that
rakes light obliquely across the face. When used in the
short-lighting configuration, as shown here, an additional reflector
or weak fill source may be used to lighten the shadows on the camera
side of the head.
Strobe fill has several advantages:
- Unlike reflectors that must be opposite a
source of light, strobes can be positioned almost anywhere.
- Some strobe monolights/heads provide
infinitely adjustable output over a range of several f-stops,
allowing for very precise control of the fill.
- Strobes can be fitted to a large number
of light modifiers, providing light with different character.
- Strobes, when paired with appropriate
modifiers, can provide a source of even fill for a very large
- Strobe fill, especially on-axis fill,
generally does not require repositioning when changing the main
Strobe fill has some disadvantages:
- Strobe fill requires an additional
lighting unit, making it a more expensive solution than
- Strobe fill often requires more working
area, especially when using the on-axis approach.
- Strobe fill may not be as portable a
- Strobe fill is best when broad-area
lighting is needed and less effective when select pockets of
shadow must be filled.
Providing the optimum amount of fill lighting
for your image is probably the most difficult and important lighting
task you'll have. The mood and feel of your image can change
dramatically with only a small change in the strength of the fill
source. And, it's not only your artistic expression that will
suffer with incorrect fill. If you are outputting your image
to photographic paper or a printing press, you'll want to keep the
brightness range (darkest detailed shadow to lightest textured
white) of the image to about 1:40 or ~5 f-stops. You'll need
the correct amount of fill to accomplish that.
MEASURING LIGHT STRENGTH
The best way to accurately measure the
strength of your strobe lighting is to use an incident flash
meter. If you do not have a flash meter, but have a digital
camera which displays a histogram, there is another way to establish
correct exposure which will be demonstrated in another section of
this site. The light-meter readings quoted in the examples on
this site are based on readings taken with the meter placed as close
to the subject as possible with the meter's hemispheric dome pointed
directly at the light source.
RELATIVE VS. ACTUAL STRENGTH
It is extremely useful to think in terms of
the relative strength when setting the output of your various lights
and, in particular, the relative strength of the main and fill
lights. Now, don't get me wrong, the actual strength of your
lighting is important. It will determine what lens aperture
you will use and this has a very important impact on the look of
your images, as it affects the depth of acceptable focus. But,
it is the relative strength of the lights that ultimately affects
the look of the lighting. Increase the strength of all lights
by a factor of 4 and the lighting will look the same, just
brighter. Decrease all lights by one f-stop and the
lighting will look the same, just darker. A shorthand for
expressing the relative strength of illumination is commonly used in
photography and is known as a lighting ratio.
Lighting ratios are used to express either the
relative intensity of the illumination in two areas of an image or
the relative intensity of two sources of light. In
cinematography, it is the latter ratio that is most often used, but
in still photography, it is usually the former. In still
portraiture, the lighting ratio is usually used to represent the
relative strength of the light that falls in the fully lighted area
(main light + fill light) to that in the shadows (fill light only).
Though one might be able to establish a lighting ratio for a main
light and its associated reflector fill, ratios are usually
used only when a separate main and fill light are employed.
On this site, lighting ratios are used to
express the ratio of the intensity of the illumination that falls in
the areas lighted by both the main and fill lights, to the intensity
of the areas illuminated solely by the fill light. This is
shown graphically below.
f.1 (on-axis fill)
Diagram f.2 (opposite-side fill)
Diagram f.3 (form fill)
Main Light Only
Fill Light Only
Combined Main and Fill Lights
SELECTING A FILL SOURCE
How you provide fill will depend on many
factors and your personal preferences. Here is my take on the
REFLECTORS AS A FILL SOURCE
Quality portraits, from headshots to
full-body shots, can be created using fill from only a
reflector. Many well-known photographers prefer this method.
Reflector fill has several advantages:
- Using the modeling light of a
strobe, the reflector can be adjusted by eye until the
desired fill is achieved.
- Reflectors are less expensive than
an additional lighting unit.
- Many reflectors fold down and can
also be used for outdoor portraiture
- Reflectors come in a variety of sizes
and surfaces, allowing you to vary the amount and
specularity of the fill.
- Reflectors can be used close to the
subject and require less studio depth than many solutions
using an additional strobe.
- When used close to the subject,
reflectors can provide very localized lightening and will
not significantly affect other areas of the scene. This
provides an advantage over more general fill lighting when
working in rooms with strongly-colored walls.
Reflector fill has several disadvantages:
- Reflectors generally require
broad-coverage light sources. Lights that have narrow
angles of coverage (narrow-beam parabolics, grid heads,
etc.) focus most of the light on the subject and provide
little that spills over to the reflector.
- Fill reflectors are normally used
close to the subject, resulting in a rapid fall-off in
fill-light intensity. This makes reflectors a questionable
choice when attempting to provide even fill for a large
area, as would be needed for group portraiture.
- Adjustments to the main light often
require readjustment of the reflector
- It can be very difficult or
impossible to assess reflector fill accurately when working
in well lighted spaces. Most photographers who work with
reflector fill do so in studios with subdued lighting.
STROBES AS A FILL
The use of a separate strobe as a fill
source is very common. Many high-volume studios use an
additional strobe as a source of fill.
Before covering the general strengths and
weaknesses of strobe fill, let's take a look at a few top-view
diagrams that depict some common implementations of strobe
The fill lighting used in the above example
was supplied by bouncing light off of a white wall behind the
camera. You don't have use a separate light to provide fill
light. Many photographers prefer to use a reflective panel on
the side opposite the main light to fill in shadows. Lighting
diagrams for two popular fill-lighting methods are shown below.
a reflector as a
a second light as a
Fill light is any source of illumination that
lightens (fills in) areas of shadow created by other lights.
Most often, fill light is used to lighten the shadows created
by the main (key) light. The fill source is generally
indistinct and lightens while not imparting character or noticeable
shadows of its own. Some images, especially those requiring a
dramatic mood, are best with little or no fill lighting.
However, most images will require some form of fill lighting to keep
the image shadows and highlights within the dynamic range of the
In the three images shown below, we
have an example of how a main and fill light are combined to produce
a finished image. The leftmost image shows a mannequin
illuminated solely by a rather hard-edged main light. The main light
provides a strong sense of relief, but the shadows are inky black
and the overall lighting harsh. The center image shows the
same mannequin illuminated solely by a fill light. The
fill light provides flat overall illumination that, by itself,
is lackluster and imparts little sense of depth. The rightmost
image shows the combination of the main and fill light.
Here the best qualities of both lights are combined to produce an
image with open shadows and an increased sense of relief`. The output of the main light in these images
is set to be approximately twice that of the fill light, providing a
fairly low ratio (3-to-1) lighting.