amount of light vs power input

it has occured to me that there must be a limit to witch adding extra lights or increasing the wattage of bulbs will be of no or very little extra help
much like decibels ; somthing can only make so much noise before the extra is power input is relatively useless,
as a double in sound pressure level is only measured as a 6dB increase no matter how loud or quiet it is. as shown on a graph ( SPL vs dB ) as a log curve

light must have a similar principle
i have looked into it and all i can find is light intensity vs distance witch is irrelavent to this
has anyone any ideas or an answer??

Yeah, sort of! The math involved with accoustics is rather different from that of grow lights. With accoustics the "exact size" of a room doesn't matter too much. With grow lights, the size of the grow area is "critical" in order to match "output power" and "square feet". As I recall it takes about 10 times the amount of "amplifier power" to just double the sound pressure level, whereas, that same ten-fold increase in "Light Wattage" (lets say from a 100 watt HPS, to a 1,000 watt HPS), would increase the potential grow area by several orders of magnitude - instead of just one!

I'm not really sure what you're asking here; but certainly, at some point, there is a "Point of Diminishing Returns". When it comes to HID lights (Metal Halide and High Pressure Sodium), 50 watts/sq. ft. is concidered "normal" (75 watts/sq. ft. may produce better results, but you'd better know what you're doing!). Much less than that and you risk being "under powered" - much more than that and you start to enter the realm of "Diminishing Returns".

Maybe 140 is the "Magic Number"! As I recall, SPL's up around 140 db can generate physical pain - 140 watts/sq. ft. of HID lighting come, pretty near, doing the same thing to plants! Except that "The Inverse Square Law (of the propogation of light)" allows for a relatively small distance of seperation to acheive a great reduction in radiated light power (twice the distance from light to plant = 1/4 the light energy received). So, just pulling the light back a foot, or so, could negate any negotive (or possitive) effects to be had from the lights!

nah, i dont think 140 watts a square foot would do any harm. many people have 600 watt lights in like 2x2 tents and such. and some with 1000w lights in there.

i get what T.H.Cammo means but the basic question was that is there a point when adding more lights dosen't make it much brighter ?
i know that 2X distance = 1/4 light
but does 2X wattage = 2X lumens

jesus christ. lowest amount of light for flowering - 3,000 lumens per square foot of growing area. take your total lumens from all lights and divide by the square footage of your growing area. recommended light for flowering 7,000 to 10,000 lumens per square foot. much above 10,000 can start to hurt your plants.

cfl 13 actual watts/60 equivalent: 850 lumens
cfl 26 actual watts/100 equivalent: 1,750 lumens
cfl 42 actual watts/150 equivalent: 2,750 lumens
cfl 68 actual watts/250 equivalent: 4,200 lumens
hps 150 watts: 16,000 lumens
hps 250 watts: 28,000 lumens
hps 400 watts: 55,000 lumens
hps 600 watts: 95,000 lumens
hps 1000 watts: 145,000 lumens

nope. lets say you have a 6x6 room and have 2 1000 watters. the emit 150,000 lumens. that does not mean you have a total of 300,000 lumens. you have 150,00 lumens that cover a greater area.

no, that is another one of those myths. the light is additive. people who say not just do not understand physics. go outside tonight with two flashlights and shine them separately on the ground. then point them at the same spot - want to bet whether it's brighter or not? what is in practice not additive is lumens per square foot, or foot-candles, to use the precise term. since the intensity of light decreases by the inverse square of distance you just can't get two bulbs physically close enough in a real world grow situation to double their foot-candles. if you put two small cfl's together with one an inch away from the bud then the other is going to be 2 inches away and only a quarter the intensity of the first, so you'd increase lumens per square foot by 25%. if you put two 1000 watt bulbs right next to each other you would come close to doubling lumens per square foot but no sane grower would do that as you'd have to keep the plants several feet from the light to avoid bleaching.

1 way 2 settle this
have 3 lights of equal type ( as close as possible ) and a light meter of some sort with LDRs and stuff
tun them on 1 at a time
plot the reading on a graph
a linear graph = additave
a curve = logarithmic

do it with more lights and it would e more accurate

i have a nist certified 0 to 30,000 foot-candle light meter and know how to use it. read earlier post.

one light over the meter:

meter reading:

two lights over the meter:

meter reading

questions?


edit - first reading is probably low because the light wasn't directly above the meter. an inch makes a big difference with cfl's

oh this is great! that clears it all up! thanks for that rep+