We're talking temperatures, here, something that is easily observable from a star's color . They actually look blue. These are high-wattage stars. Examples are Spica, Regulus, and Vega. Examples are Proxima Centauri, Barnard's star, and 61 Cygni.
Blue stars are high-wattage.
Red stars are low-wattage. Thankfully, these oddballs are rare, and stand out spectroscopically. Observe your mystery star, and see what color it is. From the color, get the temperature, and from the temperature, get the wattage. You've got the distance to the star.