Lighting is an important aspect of our daily lives. It helps us navigate, see clearly, and adds aesthetic value to our surroundings. In this article, we’ll explore some of the most commonly used terms in lighting, including footcandles, lumens, candela, luminous efficacy, luminance, and illuminance.

Footcandles, written as “fc” or “ft-c”, is a standard unit used to measure light. It is the amount of light that falls on a 12 x 12-inch square, twelve inches away from a standard ¾-inch candle. One does not need to light up an area to the extreme brightness to navigate safely at night if 1/10th fc is enough. For instance, on a full moon night, the light is sufficient to navigate outdoors and is a good point of reference when designing or installing a lighting system.


Lumens and LED lighting
With the advent of LED lighting, new terms have been introduced, including lumen or lm. A lumen measures the total amount of visible light from a lamp or light source. The higher the lumen rating, the “brighter” the lamp will appear. In the past, people used to buy conventional bulbs based on their power consumption, thinking it equates to brightness. However, this is not the case with LED lamps. For example, a 6.5W LED lamp will give a similar light output as a 50W halogen bulb, while consuming 87% less energy and producing more light. LED technology is advancing, and more lumens are produced using fewer watts, resulting in more lumens per watt.


The term “candela” is used to measure the intensity of light emitted from a light source in a given direction. It is different from a lumen, which measures total light output. One candela is equivalent to the light output of one candle. One footcandle is the measurement of one candela illuminating 1ft². One candlepower is approximately 0.98 candela.


Luminous efficacy
Luminous efficacy is how we measure the efficiency of a light source in producing visible light. It is measured in lumens per watt (lm/w) in the International System of Units (SI). For example, a 200lm LED lamp rated at 2w would have a luminous efficacy of about 100 (200/2=100).


Luminance and Illuminance
Luminance measures the light that is reflected off a surface, whereas illuminance refers to the quantity of light falling on, or illuminating, a surface. Luminance is measured in candela per square meter (cd/m2), while illuminance is measured in footcandles or “lux”. One footcandle equals approximately 10.8 lux. To put it simply, if you measure the light shining onto a wall, you’re measuring illuminance, while if you measure the brightness of the wall, you’re measuring luminance. Typically, we see luminance as we see the objects being illuminated, while we can’t see illuminance as light traveling through empty space is invisible.


In conclusion, lighting is a complex subject with a lot of terminology. Understanding the concepts of footcandles, lumens, candela, luminous efficacy, luminance, and illuminance can help you make informed decisions about lighting your space effectively and efficiently.

(Pics sourced from internet)

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