Flash on Clash is a visual effect where the lightsaber blade color briefly changes to a different color upon impact. For example, if you hit the blade against another lightsaber blade, against your hand, against the table or some other object, then the blade color will briefly change to a secondary color before reverting to the original color.
Watch What is Flash on Clash (FOC)? (Lightsaber Terminology) on YouTube
Although there are many Flash on Clash color options available, white is the most common and popular Flash on Clash option since white sharply contrasts most other lightsaber blade colors (except white, of course!).
Flash on Clash reliability varies vastly from company to company. Some custom sabers are better at detecting the impact to trigger the Flash on Clash effect than others. Some custom sabers also allow the user to adjust the Flash on Clash sensitivity of the lightsaber hilt, making it either easier or harder to trigger Flash on Clash.
Some lightsaber companies include Flash on Clash as a standard feature. Other lightsaber companies, like Ultrasabers, consider Flash on Clash to be an upgrade. Ultrasabers’ brighter TRI CREE LEDs are NOT compatible with Flash on Clash.
Unfortunately, the officially licensed Star Wars: The Black Series Force FX lightsabers by Hasbro DO NOT include the popular Flash on Clash feature.
Flash on Clash is technically a trademarked term that’s registered by Ultrasabers, but many companies use the term freely so Ultrasabers does not seem to be defending the trademark.
Flash on Clash trademark registry:
Ultrasabers Flash on Clash (FOC) color chart:
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How important to you is the Flash on Clash visual effect? Is it a ‘must have’ lightsaber feature or an effect you could do without?