Energy blade

Energy blades or plasma blades are a category of melee weapons widely utilized by the Covenant. The most common example of such a weapon is the energy sword, a traditional Sangheili sidearm and dueling weapon, but numerous types of plasma-based bladed weapons have been and continue to be used throughout the Holy Ecumene. Energy-based polearms in particular are common in ceremonial uses, and have historically been widely fielded widely in frontline roles. One of the more notably types of energy polearm is the heliolance.

Overview
A type of plasma weapon, energy blades function by trapping high-energy plasma in a shaped magnetic field. Power is supplied by a compact battery cell in the hilt, which is depleted with frequent use.

As with most plasma weapons, the color of a plasma blade is a decent indicator of the plasma's temperature. Blue or white blades burn very hot, while red- or orange-tinted ones are much less intense. This can occur deliberately as a power-saving measure in some models. However, while this is a common rule of thumb, various tricks can be used to alter the plasma's color to some extent. Blue-hot blades are effectively required to do meaningful damage to infantry energy shielding, and so are the standard setting on military-issue swords. Most mass-produced swords are limited to their standard power setting, while many aristocratic custom-forged blades can be adjusted. Second-rate swords are often limited to lower power settings due to the use of inferior power cells, indicated by their reddish coloration. Pirates, criminals and various delinquents are often seen brandishing red blades, contrasted with the aristocratic and military-issue blue- or white-hot models.

Energy swords sporting a red coloration are sometimes called "bloodblades". This is not because of their resemblance to blood; after all, Sangheili blood isn't red. A characteristic of high-intensity plasma is that it tends to more successfully cauterise wounds than their lower-intensity counterparts. Bloodblades have a tendency to leave their victims bleeding out even if the initial strike didn't kill them. On the other hand, a higher-intensity sword is a fairly clean cut and provided one survives the initial strike, one actually has decent chances of surviving. In gladiatorial and duelling contexts, this is useful as it means that an opponent cannot rely on the bleeding out from a sword slash to kill their opponent - it requires more a test of swordsmanship and the ability to get the quick killing strike.

Likewise, the glow of an energy blade is indicative of its power level. A blade built with power economy in mind, or used on a low power setting, will glow only faintly and be noticeably translucent, while high-energy blades glow white-hot and often bleed off excess plasma, sometimes obscuring the normally well-defined contours of the blade.