Blade diffusion film, sometimes called blade film, helps distribute light more evenly throughout a lightsaber blade. Blade film is commonly rolled up and installed inside the standard, cylindrical polycarbonate blades.
Without blade diffusion film, most of the light from a saber using an in-hilt LED will escape near the emitter area, creating a noticeable ‘dead zone’ in the upper section of the blade near the tip. Blade diffusion film generally should not be removed from the blade.
Comparing Glued Blade Film vs Loose Blade Film
Some custom saber companies use hot glue to secure blade diffusion film inside the blade and other companies keep the blade diffusion film loose inside the blade.
If the blade diffusion film is loose inside the blade, sometimes the film can slide out of blade when the blade is removed from the hilt. Attaching a dust cap to the end of the blade prevents the blade from sliding out and also helps prevent dust from entering the blade.
A downside of gluing the blade film is the film can wrinkle over time wherever the blade flexes during dueling or spinning and swinging the blade around.