LEDs are everywhere today. But what does L. E. D. stand for anyway?

Luminous Efficiency Device? Less Electricity Demanded?

Not quite – though both correctly describe Light Emitting Diodes. They make more light, from less electricity, than any other technology.

Incandescent bulbs of the 20th century heat a metal filament until it glows white hot. They produce light, but much more electricity is converted into, and wasted as, heat.

Fluorescent tubes pass energy through a gas that glows. They consume less electricity, but their light is not so attractive, they must be disposed of properly, and the bulbs can be fragile.

So scientists kept pushing for something better, and invented LEDs in the 1960s. The initial technology was basic and expensive, but worked the same way it does today:

Electricity flows through a two-layered semiconductor. One layer has an excess of negatively charged electrons.

The electricity forces electrons to jump to the other positively charged layer to equalize. As they do, they release a small amount of energy as light.

Multiply that over millions of electrons and these diodes can emit a great deal of light, with very little energy wasted as heat.

They’re such a step up over old bulbs, that LEDs now make up half of global lighting, and growing.

Have you ever wondered how squirrels find the nuts they hid months before?

A typical squirrel can store 3,000 of them in a fall season, in dozens of locations. It seems almost impossible that they could remember them. But they do.

There are 200 species of ground squirrel, tree squirrel and flying squirrel that rely on stored seeds and nuts.

To do that, they need to return to them even after leaves fall and snow covers the ground. How do they do it?

Smell plays a role. But sight and memory are more important.

Squirrels build a mental map of their surroundings: a tree trunk, a large rock, a fallen log, a fence post.

Then they remember the changing spatial relationships between those landmarks when viewed from their different food hiding places.

Some scientists have wondered if a squirrel’s brain grows to meet the season’s mental demands.

Because there are other rodents -- shrews, European moles and weasels – whose brains contract 10% in winter when food is scarce, then expand again in spring, with no impact on function.

But most research suggests a squirrel’s heightened spatial memory is linked to its larger than normal hippocampus, a part of the brain involved in learning and navigation.

They’ve also shown more neuron growth, and less age-related mental decline.

To fuel this acuity, squirrels require a lot of calories – which ironically means they must hide more nuts to help them find the others!

In 1985, a passenger jet landing at DFW airport was forced to the ground by an unusual downward blast of wind called a downburst. The plane struck cars on the highway and a water tank, then crashed on the airfield, killing more than 100 people.

It was the third such fatal crash in a decade. So, the FAA set out to invent a new warning system for these dangerous wind events. A downburst is a sinking column of air within a thunder cloud that accelerates toward Earth, reaching speeds over 100 miles an hour.

When it strikes the ground, it blasts out in all directions, like a mammoth version of water splashing in a sink. These winds are strongest just 10 to 30 feet from the ground and travel horizontally outward in all directions. They can fell trees like a tornado’s whirling winds, but they all fall in the same direction, like dominoes.

For aviation, the first step was training pilots to look for visual signs – expanding rings of dust on the ground below, or sharply defined shafts of intense rain.

Technologically things were more complex. Vulnerable airports installed a network of wind sensors, as well as advanced Doppler radar that could track wind speeds. All fed into an early alert system.

By 1994, 46 high traffic airports had installed these systems. They haven’t had a single downburst accident since -- and technology continues to improve. A triumph of aviation safety.