"It got very sophisticated because obviously the battery doesn't last long and then we had to look at circuits and interrupters, so we have been working on it around two months with a crack team," swimmer Andrea Fuentes said.
"It looks a bit like Christmas lights," added the Spaniard, one half of the team that won silver at the last world championships and are favourites for a medal in Beijing.
Swimming's world governing body, which sets swimsuit rules for a sport where sequins are almost obligatory, said the lights were an accessory but Fuentes still hoped they might back down.
Flawless Russia complete clean sweep
"This is a very conservative sport ... their excuse that is you cannot have accessories on your swimsuit, but they are sewn in. If you use those standards, sequins are a type of accessory."
Russia defend synchro gold
Russian champions lead