Question about lumens and lamps.

[HomerSimpson]

So I'm just wondering how lumen ratings work with regard to bulbs.

For example, using the surface area of a sphere, measures using the radius: 40,000 lumens becomes 3200 lumens at 1 ft. 2 ft is 800 lumens. 18,000 lm is 5 inches away. Correct?

Where as a 1600 lumen CFL emits 130 lm at one foot. 2 inches is 4600 lm. Once inch is 18,000 lm. Correct?

Thanks.

 

[asdalton]

No, lumens is a measurement of total light output, which is independent of distance. A lamp has a certain lumen output, period.

 

[HomerSimpson]

Ok, so then at 1 foot the lamp would have that lumen rating per sq ft?

What about getting closer to the lamp than one foot?

Since I = P / A or i = p / r ^ 2.

Would, say, a 10,000 lumen lamp, @ 6" be 40,000 lumens?

 

[StarHalo]

lumens is a measurement of total light output, which is independent of distance.

A 10,000 lumen lamp viewed at a distance of one mile is...10,000 lumens.

The lumens-per-meter measurement you're looking for is Lux: http://en.wikipedia.org/wiki/Lux

 

[HomerSimpson]

Ok. So say I have two flashlights.

And I point their beams at a single point one foot away from each of them. This would double the lux, correct?

 

[StarHalo]

If both lights have the same lux score individually, then yes.

 

[ponygt65]

ALso research "Foot Candles".

That may give you more understanding.

 

[Ken_McE]

"Lumens" is a measure of the total amount of light emitted by an object. you can change how much of that light falls on you, but you are not changing how much light it emits.

What does change is the amount of light that falls on a given surface, and this does of course shrink as you get further way. We use different units to measure how much light is recieved by a surface such as lux and foot candles.

You may be interested in: http://en.wikipedia.org/wiki/Lux

 

[HomerSimpson]

So, If I have, say four 25 watt bulbs, and compare it to a 100 watt bulb, and for the sake of this, they produce the same lumen/watt output.

If I take those 4 bulbs, and put them in a tight grid(like a square), I'd have very nearly the same lux, using those four 25W bulbs compared to one 100W, when measuring lux at identical distances between the two setups, correct?

 

[StarHalo]

So, If I have, say four 25 watt bulbs, and compare it to a 100 watt bulb, and for the sake of this, they produce the same lumen/watt output.

If I take those 4 bulbs, and put them in a tight grid(like a square), I'd have very nearly the same lux, using those four 25W bulbs compared to one 100W, when measuring lux at identical distances between the two setups, correct?

Yes.

The two setups would also have the same lumen output.

And how you direct the light can then alter those numbers; if we put a mirrored bowl over the 4x25w setup, directing the light in one general direction, that setup would then have a much higher lux rating than the 1x100w. Still the same lumen output, but differing lux throw - This is a very important concept when dealing with flashlights.

 

[ponygt65]

Yes.

The two setups would also have the same lumen output.

And how you direct the light can then alter those numbers; if we put a mirrored bowl over the 4x25w setup, directing the light in one general direction, that setup would then have a much higher lux rating than the 1x100w. Still the same lumen output, but differing lux throw - This is a very important concept when dealing with flashlights.

+1.

It's VERY important when dealing with any type of lighting. Optics/reflectance is key in some lighting setups.

Edit: Just for reference, 10lux = 1fc.

 

[HomerSimpson]

Ok, so back to one of my previous questions.

Would moving closer than 1' would increase the lux, like 6" would be 4*lumens in lm/ft^2. 3" would be 16*lumens in lm/ft^2, etc. Correct?

Thanks for the replies!

 

[asdalton]

Only if the light source is very small.

The inverse square law can be extrapolated only when the distance from the light source remains very large compared to the size of the light source. When the two sizes are comparable (for example, 1 foot away from a standard household light bulb), then you will not get such a strong increase in lux by shortening the distance.

If you think about it more, it has to be this way, or else the lux would become infinite at the surface of the light source.

 

[HomerSimpson]

Well, I was thinking along the lines of... like a candle, if you touch it you get burned... it'd seem to take a lot of lux to actually burn.

 

[StarHalo]

Lux is just a unit/expression of how much light is being emitted, not heat. A very efficient light source will emit more of the energy going into it as light and not heat.

A candle flame is not very efficient, it expels almost all its energy (~50-100 watts) as heat. The hottest point in a candle flame (the blue part) is over 1000 degrees Fahrenheit.

The image in my sigline is of a High Intensity Discharge bulb cooling down; the orange part (the arc tube, where the light is created) sees temperatures over 2000 degrees Fahrenheit; if you were to put an aluminum-bodied flashlight in that reaction, it would melt like ice cream.

 

[HomerSimpson]

What about IR 'light'?

 

[Morelite]

What about IR 'light'?

IR is measured in watts by using a infrared detector and converting the received radiation into an electrical signal. The detector can be a thermocouple, or any number of solid state devices.

 

[HomerSimpson]

I'm mainly wondering like how much the intensity can increase, I suppose.

Like I found this chart I guess it could be called a lm/sq ft(non SI lux) chart:

Is it more or less accurate? It seems to obey I = P/r^2.

 

[StarHalo]

The chart doesn't make any sense to me; For one, there's no correlation between watts and lumens. And the numbers as they're displayed there seem to imply that a 300 lumen light source would be completely invisible at a distance of just over six inches..

What "intensity" is it you're wanting to increase, lumens/output, lux/throw, or.. ?

 

[HomerSimpson]

The chart seems to have minimums of 1000 lm and 1.2". Yea... 900 lm @ 1' doesn't even make the chart... :laughing:. As far as I know the watts/lumens relate to typical CFL bulbs.

Lux/throw, I think.

I heard those Aero Garden have small CFLs in them. I was thinking of using ?? CFLs for a small indoor herb garden of basil, cilantro, thyme, maybe some others. My question is sort of how much light do I need(and how close). They don't seem to publish any PAR(µmol/area/time) ratings on these type of bulbs.

I'd like to do better than pure trial and error.

I've just heard you need them really close, like within a couple inches. Most bulbs seem to be over 40,000 lm/sq ft within 2 inches.

I'm just wondering, if it doesn't increase between 1' and 1".... then would 1 foot be the same as 1", in lm/sq ft(or lux)? Is this what you're telling me?

I like your signature picture. It's pretty.