In defining how bright something is, we have two things to consider. 1. How bright it is at the source- where the light is originating. 2. How much light is falling on an object a particular distance away from the light. Foot Candle: Why Candle Foot? Well since we are in the USA, its more patriotic to use the Candle Foot vs. the Lumen (they are both essentially the same thing). Here is a good example. Get a cake candle. Grab a ruler or tape measure. Stick the candle on one end of the ruler. Light the candle. Turn the lights out (so that the room is dark). One foot-candle of light is the amount of light that candle generates one foot away. That’s a useful unit of measurement. Why? Say you have a light bulb. You are told it produces 200 foot candles of light. That means at one foot from the light bulb, you will receive 200 foot candles of light. But here’s where it gets tricky. The further away you move the light from what you want to illuminate, the less bright the light appears! If you measure it at the light, it’s just as bright. But when you measure at the object you want illuminated, there is less light! LUMENS is a unit of measurement of light. It measures light much the same way. RADIANCE is another way of saying how much light radiating from the light itself. The heat is usually measured. ILLUMINANCE is what results from the source of light. ILLUMINANCE, is when you shine a light in a dark space therefore lighting the space up. ILLUMINANCE is a measurement of the total light being seen in the dark space. LUX, is the metric version of ILLUMINANCE. Candlepower is a rating of light output at a bulb source, converting with English measurements. Foot-candles, is a measurement of light on an illuminated object. Lumens is he metric equivalent of a Candle foot. Divide the number of lumens you have, by 12.57 and you get the candlepower equivalent. LUX is the metric version of ILLUMINANCE.