How to Gel Your FJ400 Strobe for Color Accuracy

By Westcott | Published: 2026-10-18

Category: How-to Guides

Learn how to attach and position color correction gels on your FJ400 strobe for accurate white balance and creative color control using FlexiGels.

Quick answer

Slide a FlexiGel over the front of your FJ400 strobe (or over a modifier like a Rapid Box) to instantly shift color temperature or add creative tint without tape or adapters.

Why gel placement matters for color accuracy

Gelling a strobe isn't just about adding color — it's about matching your light source to your scene's white balance. If you place the gel too far from the flash tube, you risk uneven color across the frame. The FJ400's flash tube sits close to the face of the strobe, so a gel that wraps directly around the tube or sits flush against the modifier opening gives the most consistent color.

The FlexiGels Classic Pack is designed to slide securely over the FJ800, FJ400 II, FJ400, and FJ250 strobes, making placement simple and repeatable. Because the gel sits close to the light source, you get even saturation without hot spots or color fringing.

When to use a gel vs. a gel on a modifier

If you're using a bare FJ400 strobe, slide the FlexiGel directly over the flash tube. This works best for direct flash or when you want full color saturation. If you're using a softbox or umbrella, place the FlexiGel over the front of the modifier instead. The patented design holds the gel flat against the fabric, so you still get even color but with softer falloff.

The trade-off: gelling the modifier gives softer color but may reduce output slightly more than gelling the tube directly. For critical color correction work (matching ambient tungsten or fluorescent), gelling the tube is more precise.

How to attach a FlexiGel to your FJ400 strobe

Choose the right gel for your goal: For color correction (matching white balance), use a CTO (orange) gel to warm flash to tungsten or a CTB (blue) gel to cool flash to daylight. For creative color, pick any FlexiGel from the pack. A common mistake is using a creative gel when you need a correction gel — check the gel's label before attaching.
Slide the gel over the flash tube (bare strobe): With the strobe off and cool, hold the FlexiGel by its edges and slide the open end over the FJ400's flash tube until the gel sits flush against the strobe face. The patented design holds it securely without clips or tape. If the gel feels loose, it may be on backward — flip it so the open end faces the strobe body.
Or attach the gel to a modifier: If using a Rapid Box Switch or umbrella, stretch the FlexiGel over the front fabric opening. Center the gel so it covers the entire modifier surface evenly. Gapping between the gel and modifier fabric causes uneven color — smooth the gel flat with your hands after attaching.
Set your white balance: After gelling, take a test shot with a gray card or white reference. Adjust your camera's white balance to match the gel's color temperature (e.g., tungsten for CTO, daylight for CTB). For creative colors, set white balance to flash and adjust in post. Relying on auto white balance after gelling often gives inconsistent results — always use a custom or preset white balance.
Test for even coverage: Fire the strobe at a white wall or seamless paper. Look for hot spots (brighter areas) or color shifts at the edges. If you see uneven coverage, reposition the gel or check that it's fully seated. A hot spot near the center usually means the gel is too close to the tube — pull it forward slightly to diffuse the light.

Products mentioned

FlexiGels Classic Pack (FJ800, FJ400 II, FJ400, FJ250): 8-pack of reusable, flexible color gels for the FJ800, FJ400 II, FJ400, and FJ250 strobes. Includes Vivid Red, Orange, Yellow, Green, Teal, Blue, Purple, and Pink. You get a full palette of creative colors plus the ability to layer gels for custom tints, all without needing adhesive or clamps.
FlexiGels Classic Pack (FJ800, FJ400 II, FJ400, FJ250)
Original FJ400 Flash Tube: User-replaceable flash tube for the Original FJ400 Strobe that attaches quickly to the face of the strobe. If your tube wears out from frequent gelling or handling, you can swap it yourself instead of replacing the entire strobe.
Original FJ400 Flash Tube