Roullette
Well-Known Member
this explains how lumens are measured
Lumens, Footcandles, Candlepower, Measuring Light Output
but this is basically how it is measure this is a paste from that site.
[FONT=Arial, Helvetica, sans-serif]A LUMEN is a unit of measurement of light. It measures light much the same way. Remember, 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.[/FONT]
[FONT=Arial, Helvetica, sans-serif]So, if we take your candle and ruler, lets place a book at the opposite end from the candle. We'd have a bit of a light up if we put the book right next to the candle, you know. If that book happens to be one foot by one foot, it's one square foot. Ok, got the math done there. Now, all the light falling on that book, one foot away from your candle equals both…….1 foot candle AND one LUMEN![/FONT]
[FONT=Arial, Helvetica, sans-serif]and i found this on another sight.
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This is a real easy way to find the number of Lumens Per Square Foot (Foot-Candles) you are getting from your bulb at any distance. It’s the same value you’d get using the more complicated formulas below, but is real quick and simple.
- Multiply the lumen output of the bulb by 45.84.
- Divide by the number of inches from the bulb squared.
This would be based on the use of a typical 120° reflector. If the reflector cast a different angle, then we would need to manipulate the formula a bit as is shown below. It’s all based on spherical geometry.
This is the longer detailed formulas for calculating the number of Foot-Candles (Lumens/ft.²) coming from a bulb:
The divisor must be equal to the actual area that is being illuminated by the bulb, which is not based on your floor plans. The divisor in Formula A is calculating a spherical propagation of light, which is what the light is really illuminating.
Formula A:
Foot-Candles = Lumens ÷ (4 × Pi × d²)
Where:
d = The distance from the bulb in feet.
Pi = 3.14159
If you wanted to know how many Foot-Candles of light are striking your plant 10" away from a 400 watt HPS that puts out 50,000 lumens you would do this:
Foot-Candles = 50000 ÷ (4 × Pi × (10/12)²)
Foot-Candles = 50000 ÷ (12.57 × 0.6944)
Foot-Candles = 50000 ÷ ( 8.729)
Foot-Candles = 5,728
So, there are 5,728 Foot-Candles of light hitting your plant 10" from a 400 watt HPS with no reflector.
Now, because we are using reflectors it will actually be more. Let's calculate how many Foot-Candles hit your plant 10" away with a typical 120° reflector.
Formula B:
Foot-Candles = Lumens ÷ (2 × Pi × d² × (1 - cos(A/2)))
Where:
A = The degree of the reflector. (Most of us have 120° reflectors)
d = The distance from the bulb in feet.
Pi = 3.14159
To make this easier we already know the value of d² when the distance is 10" from the bulb. That value as calculated above is 0.6944.
Foot-Candles = 50000 ÷ ( 2 Pi × d² (1 - cos(120/2)))
Foot-Candles = 50000 ÷ ( 2 Pi × d² (1 - cos(60)))
Foot-Candles = 50000 ÷ ( 2 Pi × d² (1 - 0.5))
Foot-Candles = 50000 ÷ ( 6.283 × 0.6944 × 0.5)
Foot-Candles = 50000 ÷ (2.181)
Foot-Candles = 22,918
so there for the only difference i can see HPS being better is spectrum and possibly the reflector but mylar works like a champ for me so i guess im getting the most out of my lumens.. but i cant find anything on how spectrum effects the plant.. Is a 2100K vs 2700K spectrum bulb the the difference in yield? i cant see how the color of light would reflect on how big your yield is.
like mattso101 said do what works for you.
but imma go with a low heat transfer lighting.. fly overs is what gets your busted. even if you have your room cooled just that sodium tube glowing is like a million degrees.and if your a retard and make the oinks come to your door or have a sick ass grow op making your electric meter spinning like a roulette wheel those are a few other ways to get bopped. but low heat Xfer for me.
as of lumens from a HO Fluors you can get lower branches better due to the low PAR rating of HO lights just sacrificing spectrum and using 123 more watts for your 50,000 lumens.
