Radiant Helms are the creation of the drow, and incorporate the underdark ore whose radiations are the source of so much of the power of the dark elves. A Radiant Helm looks like a crown constructed from the legs of a large, poisonous spider, and is paired with an ornate stone throne, with a similar design motif. The helmsman using a Radiant Helm must sit on the throne while wearing the crown on his/her head. When in use, a Radiant Helm radiates a strange aura which can only be seen with infravision. The Helm will only function for a drow priest or mage, or another spellcasting creature who also has innate spell-like abilities.
A Radiant Helm operates exactly as a Major Helm in most respects, including determining the SR of the craft powered, however it has certain differences. First, a Radiant Helm will only function on a vessel with a hull which has been specially designed to capture and augment the magical emanations of the activated underdark ore within the Helm. This ship hull must be crafted from a secret combination of metal alloys, artificial ceramics, and quantities of underdark ores. To date, the only vessels with the appropriate hulls are Jade Spiders and Jade Spider Commandships. When used on a ship with such a hull, the Radiant Helm can provide motive force for up to 100 tons, and can also allow its ship to carry as much as 50 tons worth of other vessels with similar hulls. The ships carried must be in physical contact with the vessel powered by the Radiant Helm, and cannot be simply towed. A strange quirk of the Helm means that, despite the fact that under the right circumstances it can move 150 tons worth of ships, it cannot power a single vessel which is larger than 100 tons. It should also be noted that, if the ship powered by the Radiant Helm is smaller than 100 tons, it is able to tow a ship with a more normal hull, as long as the towed ship would not bring the tonnage above 100. For example, if equipped with a Radiant Helm, a Jade Spider Commandship (100 tons) could carry 5 Jade Spiders (10 tons each) on its hull, but cannot tow any ships. A Jade Spider, however, could tow as much as 90 tons worth of normal ships, in addition to as many as 5 Jade Spiders carried on its hull (although it would be extremely difficult to physically arrange this).
Perhaps more important to the drow, a Radiant Helm paired with an appropriate hull allows their magical armour and weapons to retain their power away from the underdark. A ship with such a hull emmanates magical radiation which mimics that found naturally in certain areas of the underdark, maintaining the drow equipment. These hulls, however, will only provide this radiation for a period of one week without being recharged. The Radiant Helm is the method by which the drow recharge their hulls. As long as a drow hull is powered by a Radiant Helm for at least 1 day every week (not necessarily 1 continuous day), the hull will continue to provide the radiations needed. This functions even if the ship hull is carried by a ship with an operating Radiant Helm, with the result that Jade Spider vessels need not have a Radiant Helm as long as they operate closely with a Jade Spider Commandship with a Radiant Helm, which will carry them.