The Spark Lens was Krishna Sadhana's transformation item, he used the item to transform into Ultraman Tiga. Later in 'Ultraman Tiga: The Final Odyssey' there was a Dark Spark Lens that enables Krishna to transform into Tiga Dark.
Krishna gained the Spark Lens immediately after merging with the Tiga statue, which appeared in his person after he transformed back. It is apparently his by default as the reincarnation of Tiga he was destined to receive it. The Spark Lens was activated by pressure on the grip. At times, Krishna has transformed without it as he was under emotional stress or during a great fall, such as when he first transformed into living light and merged with the Tiga Statue or when he saves Dinosauroid Eve from plummeting to her death in episode 23. During those times Krishna transforms using sheer willpower.
Dark Spark LensEdit
The Dark Spark Lens is Krishna Sadhana's second transformation item. Dark Spark Lens is a dark version of Spark Lens, hence its name, which allow Krishna to transform into Tiga Dark. As Tiga Dark is implied to be the original form of Tiga, the Dark Spark Lens is implied to be a copy of the Spark Lens' original form.