Spare Bulb

Spare Bulb is a Blackout Trinket: it increases your Blackout light radius by 25%, and it also enlarges the light of any Toon that produces light. The Light-Producing Toons are Astro, Brightney, Connie, Eclipse, Rudie, Soulvester and Vee, so the bulb gives them a wider circle to guide teammates in the dark. The wiki also notes that it can be stacked with other sources of light radius.

The question is how often a Blackout happens. Floor Events begin with a 5% chance from floor 3, rise by 2% per completed floor and cap at 30% at floor 16, and Blackout is only one of the possible events (cards such as Electrician and Sparkplug reduce it further). So the bulb is dead weight on most floors and valuable on a few. The wiki's advice is to use it only if you struggle against Blackouts, or if you want to guide starters with a Light-Producing Toon. It can also help against Twisteds with long detection, like Pebble's 125 direct vision, or ranged attacks, though Brightney or Vee give more information with less risk.

Research is on Twisted Brightney, an Uncommon, and the Brightney Toon needs 1250 Ichor and experiencing 5 Blackouts. The Trinket has no Ichor price and is available now.