Light is an electromagnetic radiation, visible to the human eye only within the wavelength of 400-700 nm.
This electromagnetic radiation is measured according to the following three dimensions:
- Light luminance intensity (perceived by the human eye as the light intensity), it is measured in cd (Candela – Latin for candle). Here are several examples:
Ordinary candle = 1 cd
Ordinary 100W lamp = 100 cd
Energy savingCFL bulbs of 20W = 100 cd
Enery saving LED lamps of 5W = 30 cd
- Wavelength (perceived by the human eye as the color of the light), in accordance with its wavelength, the human eye perceived the light in different colors.
Here are the different colors depending on the light’s wavelength:
red ~ 700–630 nm
orange ~ 630–590 nm
Yellow ~ 590–560 nm
green ~ 560–490 nm
blue ~ 490–450 nm
violet ~ 450–400 nm
-Light polarization – the polarization of the light is not visible to the human eye, but can be viewed through various types of filters.
There are several more measurement units used for the measurement of the various aspects of light, and everything associated with lighting and illumination:
- The intensity of the light flow (how much light is contained in one area) is measured in Lumens (lm). Here are several examples:
Ordinary candle = 11 lm
Ordinary 100W lamp = 1100 lm
Energy saving 20 W CFL bulbs = 1100 lm
- the color temperature is measured in K (Kelvin) degrees – these degrees show the temperature which is needed to heat an absolute black body (this is a theoretical object, which doesn’t exist in the natural world) in order for it to emit light in the same color. Here are several examples:
Ordinary candle: 1900 K
Ordinary lamp: 2700K
Energy saving CFL bulbs: from 2700 to 6500 K
Midday light: 6500K
- Illuminance is measured in Luxes (lx). When we spread 1 ml of light on an area of 1 sq.m., from a distance of 1m, then its illuminance is 1 lx.
The high quality lamps and lighting products are always marked with the amount of Lumens of their light flow, as well as the light color.
