Atmospheric
Optics
Fireflies
~ Astronomy writer Bob King captured this magical scene of fireflies darting and signalling in the evening gloaming. Jupiter blazes at upper left.
Images ©Bob King, shown with permission
Firefly
luciferin
Light production is by chemical reactions. It is highly efficient (+50%), more efficient than our LED lighting (5-15%) and especially filament lamps (2%).
A molecule, called generically a luciferin, is acted on by an enzyme ( generically a luciferase). Oxygen, magnesium ions and life’s ubiquitous energy transfer molecule ATP (adenosine triphosphate) are necessary too. The reactions take place at a specific site on the surface of the large enzyme molecule that act as a catalyst. Luciferin reacts with ATP. Then the product reacts with oxygen to form a compound (dioxetanone) with a peroxide ring. The unstable peroxide splits off carbon dioxide leaving an electronically excited oxyluciferin. That in turn emits the photon we see.
We copy its lantern. Light produced inside the firefly's abdomen has to get out. There is always a light loss when going from a highly refractive medium into air. The firefly smartly minimises this with a sharply stepped 'factory roof' transparent 'lantern'. Recently, researchers have mimicked the design to increase the overall efficiency of a test LED by 55%.
Firefly flashes and trails enchant the evening air.
They are winged beetles and emit their light continuously and in measured flashes from specialised cells in their abdomen. The light is to signal and in particular to attract and accept a mate. Sometimes thousands synchronise their flashes.
Fireflies are fond of pond and stream margins, marshy land or damp forest floors. They are not travellers, they are born and live their lives in one spot.
Human activities are reducing their numbers. Loss of habitat and increasing light pollution are thought to be factors.
Perhaps we can have our poorly shielded bright security lights or we can have fireflies and the stars.
