Light is best described as a form of energy and is part of a broader range of the electromagnetic spectrum. Electrical, radio waves and microwaves to gamma rays form this electromagnetic spectrum. The visible light spectrum is a relatively small portion of this spectrum, between 380 nm and 760 nm. In general, light is often defined as including the infrared and ultraviolet regions too.
Generally, the total light energy emitted from a source or falling on a surface can be measured. The measure “Lux” for light has an interesting legacy. Lux is the illumination strength of light striking a certain location. The term was born initially to describe the amount of light that will reflect on the earth on a full-moon-clear-sky night. But the quantum of light has undergone change too. A measurement of 1 lux is equal to the illumination of a one metre square surface that is one metre away from a single candle.
1 lux equals 1 Lumen/m2, in other words – light intensity in a specific area. Lux is used to measure the amount of light output in a given area. One lux is equal to one lumen per square meter. It enables us to measure the total “amount” of visible light present and the intensity of the illumination on a surface.
Today there is an instrument called Lux Meter. This lux meter is capable of calculating and displaying the average values of illumination on an LCD screen.
When it comes to emergency lights, an interesting teaser would be, that it existed before mankind. In the night the sun is hidden and the moon illuminated by the reflexion of sun rays. So, in that sense, should not we call the moon an emergency light?