The current system for lights where the user can change the radius, intensity, and falloff independently is quite unrealistic, never mind the formula used for falloff is nothing at all like real life. Furthermore the fact that the power consumption of a light is not affected by its brightness is a glaring gameplay flaw. I propose a more realistic system that should look good, while also taking into consideration performance constraints.
To begin with, the sliders for radius intensity and falloff are all removed and replaced with a single slider for brightness (rated in lumens). The power consumption of the light should be directly proportional to this slider.
The real formula for falloff is brightness / distance^2, however this results in a light level that is never 0 giving lights infinite range which is terrible for performance.However, having an arbitrary cutoff would cause an unsightly line where the light suddenly stops. Instead I propose first calculating the range of the light as sqrt(lighting_quality / brightness). Then have the formula for falloff be brightness * (range - distance) / (range * distance^2). This results in an almost identical curve, only it linearly tapers off so the light smoothly fades away at the cutoff.
The lighting quality is a graphics option that players can set in their clients which effectively determines the maximum range of lights. This gives players control over the trade off between performance and aesthetics. This setting should be controlled by a slider between a small positive value (for maximum performance) and a very large positive value (for maximum light quality).
This all should apply to spotlights as well, but due to spotlights focusing all their light into a narrow field of view, they should be able to get several times more effective brightness for a given power consumption. Also, do the same for the engineer's personal spacesuit spotlights as well as the spectator spotlight.