It sounds strange to use a flash on a sunny day, but it is one of the most useful flash techniques. The sun creates dark shadows under eyes and noses, and backlit faces often fall into shadow. A small amount of flash, called fill flash, lightens those shadows while the sun still does most of the work. The result looks natural, not like flash. This lesson explains how much flash to use and how to deal with the challenges of bright light.
What is fill flash?
Fill flash is a low-power flash added to a scene that is already lit by another main light, usually the sun. The sun stays the main light, called the key light; the flash only lightens the shadows. This is the same job a reflector does, which you learned in reflectors and diffusers, but a flash works at any angle and distance and does not need someone to hold it.
| Fill flash | Key (main) flash | |
|---|---|---|
| Main light | The sun or existing light | The flash |
| Flash strength | Weaker than the ambient light | Stronger than the ambient light |
| Look | Natural; shadows just lighter | Flash-lit look; often darker background |
When fill flash helps
- Harsh midday sun: lightens dark shadows under eyes, nose and hat brims.
- Backlit subjects: lights the face while the sun creates a rim from behind, as in backlighting and rim light.
- Bright backgrounds: lets you keep a bright sky or beach in the photo while the subject is still well lit.
- Catchlights: adds small sparkles to the eyes.
How much flash?
For natural-looking fill, the flash should be weaker than the daylight. A common starting point among photographers is about 1 to 2 stops below the ambient exposure.
- Set the exposure for the scene as if there were no flash, often exposing for the background or sky.
- Turn on the flash in TTL and set flash exposure compensation to about −1 to −2, as explained in TTL and manual flash.
- Take a test shot and check the shadows on the face.
- Adjust: more fill if shadows are still too dark, less if the face looks flashed.
Tip:If people can clearly tell flash was used, it is usually too strong for fill. Good fill flash is noticed only by its absence.
The sync speed problem in bright sun
Bright sun often needs a fast shutter speed, especially with wide apertures for background blur. But normal flash is limited to the sync speed, often around 1/200 to 1/250, as you learned in understanding flash.
| Option | How it helps | Trade-off |
|---|---|---|
| Smaller aperture | Lets you stay at sync speed | More depth of field, less background blur |
| Lowest ISO | Reduces brightness | Limited range |
| High-Speed Sync (HSS) | Allows faster shutter speeds with flash | Flash power drops a lot; works best close to the subject |
| ND filter | Darkens everything so sync speed works at a wide aperture | Also reduces the flash, so more flash power is needed |
Remember:Because fill flash needs only a little power, High-Speed Sync usually works well for it, especially at close range. Using flash to overpower the sun completely needs much more power, often from larger studio-type flashes.
Fill flash and color
Flash is close to daylight in color, so it usually blends well with sun. At golden hour, though, the sun is warm while flash is neutral, so the face can look cooler than the background. Some photographers put a thin orange gel (a colored filter) over the flash to warm it. Gels are covered in creative lighting techniques and color matching in mixed lighting.
Common mistakes
- Fill flash too strong: the subject looks flashed and the background too dark.
- Forgetting sync speed: dark bands or overexposed backgrounds; use a smaller aperture, HSS or ND.
- Standing too far away: small flashes, especially in HSS, lose power quickly with distance.
- Using fill flash for distant groups: it may not reach; move closer or use a reflector.
How professionals use fill flash
Outdoor wedding, portrait and event photographers use fill flash constantly: backlit couples at sunset, guests in harsh sun, children under trees. Most use TTL with negative flash compensation for speed, and HSS when they want wide apertures. Some prefer a reflector for its softer, more natural look, and switch to flash when distances or angles make a reflector impractical.
Practical examples
A family at noon
- Situation
- Strong sun gives the family dark shadows under their eyes and hats.
- What to do
- You add on-camera flash in TTL with −1.3 flash exposure compensation.
- Why it works
- A gentle burst lightens the shadows while the sun remains the main light.
- Result
- Natural-looking faces with clear eyes and no harsh shadows.
A backlit bride at sunset
- Situation
- You want the sunset glow behind her, but her face is in shadow.
- What to do
- You expose for the sky, then add flash at −1 compensation using HSS at f/2.8.
- Why it works
- The flash lights her face; HSS allows the fast shutter needed for a wide aperture in bright light.
- Result
- A glowing rim, a colorful sky and a softly lit face.
Key points
- Fill flash lightens shadows while the sun remains the main light.
- Start with about 1 to 2 stops less flash than ambient (FEC −1 to −2).
- It helps with harsh sun, backlit subjects and bright backgrounds.
- Handle sync speed with a smaller aperture, low ISO, HSS or an ND filter.
- Good fill flash looks natural; if it is obvious, reduce it.
Frequently asked questions
What is fill flash?
How much fill flash should I use?
Why use flash on a sunny day?
What if my shutter speed is above sync speed?
Conclusion
Fill flash is a gentle helper: the sun stays the main light, and a little flash lightens shadows and lights backlit faces. Start about 1 to 2 stops below ambient, manage sync speed in bright light, and keep it subtle. Next, you will take the flash off the camera to control its direction completely.
Finished reading? Track your progress through Flash and studio lighting.