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09-05-2009, 06:03 PM #25Senior Member
Wilting at Week 6 of flowering
Originally Posted by 420NLGuy
we must all be morons and you are a freaking genius!
"a foot-candle is how bright the light is one foot away from the source. A lumen is a way of measuring how much light gets to what you want to light! A LUMEN is equal to one foot-candle falling on one square foot of area.
"RADIANCE is another way of saying how much energy is released from that light source. Again, you measure it at the source."
"Illuminance is the intensity or degree to which something is illuminated and is therefore not the amount of light produced by the light source. This is measured in foot-candles again! And when people talk about LUX, it's illuminance measured in metric units rather than English units of measure. To reinforce that, LUX is the measurement of actual light available at a given distance. A lux equals one lumen incident per square meter of illuminated surface area. They're measuring the same thing, just using different measurement units.
"Nowadays we use the term CANDELA instead of candlepower. Candlepower, or CANDELA is a measure of how much light the bulb produces, measured at the bulb, rather than how much falls upon the thing you want to light up."
"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 seems! 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! A Physics teacher is going to tell you that light measured on an object is INVERSELY PROPORTIONAL to the distance the object is from the light source. That's a very scientific and math rich way of saying, the closer you are to the light bulb, the brighter that bulb is. Or, think of it this way. You can't change how much light comes out of your light bulb. So, to make more light on an object, you have to either move the light closer, or add more lights"
you can find out more here.
"Wattage is a measure of electricity consumption, that's all. Technically wattage has nothing to do with light (how much light does a 1000 watt hair dryer give off?), however if you are talking about wattage of bulbs, and the ratio of the amount of light given off by a certain type of bulb to the wattage it consumes is somewhat predictable, then sometimes we talk about wattage as if we were talking about light intensity.
Lumens is a measure of light intensity at a fixed distance of one foot on a fixed area of one square foot. Furthermore, lumens measures only certain (visible to humans) frequencies of light. But again, the relationship is somewhat linear so we often use the term lumens when talking about light intenstity. Lumens is getting closer to the concept, but in reality lumens is a standardized measure for comparing bulbs one to the other, not for measuring how much light is being given off.
For example, take a bulb rated at 10,000 lumens and move it half the distance closer to the plant, and what happens to the lumens? Nothing -- it's still a bulb rated at 10,000 lumens. But as we know that light intensity is inversely related to the square of the distance, moving the light to half the distance increases the light intensity four-fold."
-shake
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