foot-candle:

It is the Unit of Illuminance or Light Intensity, Equivalent to the Illumination produced by a source of one candle at a distance of one foot and equal to one lumen incident per square foot.

In simple, take one candle and one ruler. stick the candle at one end of the ruler. Light the candle and turn off the lights. so, the one-foot candle of light is the amount of light that candle generates one foot away. Take another example, we have a Lamp, and we say that our lamp can produce 100-foot candles of light. that means at one foot from the lamp, we will receive 100-foot candles of light.

Lux:

A Lux is the abbreviation for Lumens Per Square Meter and it is standardised unit of measurement of light level intensity, which is commonly referred to as Illuminance or Illuminationone Lux is equal to one Lumen per square Meter surface that is one meter away from a single candle.

Example of the wide ranging lux of a Natural ambient light conditions are given in the table below.

Sunlight Provides many thousands of lux to only a few hundred depending on the weather conditions time of day. the Lux of artificial indoor lighting is typically 500 lux or below.

We need Minimum 50 foot-candles Light to make the visual inspection, remember? so what does it mean? It's mean that The Light Produced by a source of 50 candles at the distance of one foot. and it will be equal to 50 Lumen incident per square foot.

What is Candela?

Now a day, we use the term Candela instead of Candlepower. The candela of Candlepower is a Measure of how much light the bulb produces. Candela measured at the bulb, rather than how much falls upon the thing we want to light up. Candela is not the same as a foot-candle. A Candela is a measurement of the light at the source, not the object we light up.

Converting foot-candle to Lumens:

One foot-candle is equal to 10.76 lumens. so, in order to convert foot-candles to lumens, we need to take the amount of foot-candles that we measured using light meter. suppose, we measured 50 foot-candles light, and we multiple by 10.76 to get the number of lumens.

50 x 10.76 = 538 lumens

Converting Lumens to watts:

Watts measure the amount of energy required to light products. while lumens measure the amount of light produced. One lumen is equal to 0.001496 watts. so, in order to convert lumens, we need to multiply the total number of lumens by 0.001496.

For example - Above, we convert 50 foot-candles to Lumens and the result was 538 lumens. Now let's convert this lumens into watts.

538 x 0.001496 = 0.805 watts/square meter

• Summary:
  

  » Candlepower: It is the Measurement of light produced by the source.
  » foot-candle: It is the Measurement of light at an illuminated object.
  » Lumens: It is the metric equivalent to foot-candles in that they are measured at an object we want to illuminate.