Ever since the world came to be, light has always remained a very vital part of the universe. Without light, darkness will simply rule the world. The power of light cannot be ignored in any sector of life.   The Sunlight and the moonlight have great impact in our world.   The same scenario holds for electric light.  We can’t do without   incandescent bulbs, fluorescent tubes, LEDs, halogens and other light sources.  In this write-up, the practical aspects of electric lighting systems and sources are discussed.

By way of simple definition, light refers to electromagnetic waves   with wavelength that is in the visible range.  The light referred to here is simply the electronic type found in bulbs, fluorescent tubes and other light sources.  The real energy that is associated with light waves is usually measured in watts.  The actual quantities used to characterize light in the physical realm are known to be radiometric.

Generally, light appears in specific color forms   when looked upon.  In most cases, the way   it appears depends on what the human brain and eyes observe.  It’s has been discovered that the human eye responds to approximately 380 nm to 780 nm wavelengths.  This usually gets more complicated since the eye’s response varies according to the individuals involved.  The relative condition of the observer matters a lot here.  What someone sees may be different from what the other sees because of certain physical and health conditions that may come into play.

Meanwhile,   the actual quantities used to characterize how light is perceived are said to be photometric. This is very vital in the study of   various kinds of light sources and systems.  Most scientists and engineers that have a lot with light mainly focus on the density and color of light systems.  They consider the amount of light emitted and the level of illumination   reflected by the light source involved.

In any case, there’s always the need to discover how the end user perceives the light source he or she is using.  For most architects, only the color temperature and the lumens are more important.   For the Cockpit instrument engineers, only the light intensity matters.  The LCD screen engineers pre-occupy themselves with the brightness of light while many lighting designers    focus more on the irradiance of light.   However, the case is quite different with the local consumer.  For him or her, color rendition is much more important.  From the above, it’s very clear that light means different things to different people in various professions.  Your position or profession determines which aspect of light you find most important.

The Power of Light
Light has tremendous power in our world.  It has the awesome capacity of chasing darkness out of a place.  It also keeps the environment alive and shinning.   The power of light is indeed very limitless. 

In technical terms, the power of light can be viewed from it radiation capability.  As a radiation element, the energy produced by light is usually measured in joules.  The rate of the joules is normally given in watts.  This accounts for the radiometric quantity and the radiated energy per second seen in light.  The energy here is proportional to the frequency of light through the Planck as seen in the popular Einstein equation “E= hf” where   “h” stands for “Planck” and “f” stands for frequency.

Oftentimes, light is also measured by it wavelength   capacity.  For instance, 475 nm refers to blue light while 650 nm refers to red light.  The blue light has the shorter wavelength while the red light has the longer wavelength. 

There’s also the Ultraviolet (UV) light which showcases when the spectrum is further stretched out.  The wavelength   is even shorter than blue light.  The UV also has higher energy than the visible light.   At the other end of the spectrum is the infrared light (IR). It has a longer wavelength than the red light.

Again,   a light with a single frequency is said to be “monochromatic”.  It normally has a single color. However, many light sources   do have mixed colors.  Their radiant power is usually the sum total of their power at each frequency.

Meanwhile, the term “radiant power” is usually replaced by “Radiant flux” when referring to light sources.  The term “Flux” is the total power radiating out in all the directions irrespective of how the area intercepts the light.

Radiometric Vs Photometric
Light sources as said earlier are measured by radiant flux.  If light is considered by the way it’s perceived through the human eye, and then radiant flux as weighted by the spectral response of the eye will be used to derive the luminous flux. This is usually measured in “lumens” (lm).  Generally, all the quantities weighted by the human eye response are said to be photometric.  Hence, for every radiometric measure, there’s an equivalent photometric measure attached to it.  The photometric quantities are normally measured in lumens.   Actually, the word “photometric” refers to the visible range of light which is usually sensitive to the human eye.    In most cases, bright light vision also known as “photopic vision” is used to measure the photometric quantities as opposed to night vision or “scotopic vision”.

The photopic vision usually peaks at 555 nm yellow green.  Actually, the human eye is very sensitive to the green color. This is usually the why a green laser pointer normally looks brighter than red or blue pointers that have the same power.  On the other hand, the “scotopic vision has a similar shape sensitive curve. However, this is shifted to the blue color with shorter wavelength.  It peaks at 510 nm.  The scotopic vision is also known to be more sensitive to light than photopic vision. Meanwhile, there’s a middle portion between photopic and scotopic vision where both meet. That portion is known as “mesoscopic vision’

In all, when it comes to the power of light as it concerns light sources, CFLs and LEDs are said to be twice efficient as incandescent bulbs.  This is because of their unique spectrum and eye response.  CFLs actually have narrow spectrum while LEDs have wider spectrum.