The insect considered to be the most bioluminescent is the firefly (Pyrophorus noctilucus) which has been documented as having a surface brightness of 45 millilamberts. The light emitted by fireflies (which are actually beetles, not flies) is unique as almost 100% of the energy is given off as light. In a lightbulb only 10% of the energy is light with the other 90% given off as heat.

A lambert is a unit of luminescence and equals 3,183 candelas/m²
A millilambert equals 3.183 candelas/m²
A candela is the base unit for measuring the intensity of light

They are usually between 10 and 14mm long, weight: 0.3 g, lifespan: 10 days, discovered: 1758.