Light wave sickness

Light wave sickness was a sickness fatal to the Daleks but not fatal to Spiridons. The Daleks conquered Spiridon, hoping to discover the secret of the Spiridons' invisibility and reproduce it for their own use on an army kept in suspended animation. Only one Dalek used it, but it died from light wave sickness. The invisible Dalek was discovered by the Third Doctor and a group of Thals. (TV: Planet of the Daleks)

After being the Daleks' prisoner for many years, the Seventh Doctor released a contagion that gave the Daleks the light wave sickness. (AUDIO: Return of the Daleks)