They are unknown for the firefly, so that its luminous efficiency only as a light-source can be determined.
The luminous efficiency of a light-source is distinguished from that of a lamp.
In these figures the luminous efficiency is the shaded area ÷ total area, 0.43 per cent.
This lamp, known as the magnetite-arc, has a luminous efficiency of about 20 lumens per watt with a clear glass globe.
It immediately became possible to operate it at a higher temperature with a resulting increase of luminous efficiency.
These methods produced fragile filaments, but their luminous efficiency was higher than that of previous ones.