Lumens 1

[MadMango]

From what I can determine, one footcandle is equal to either one lumen per square foot, or one lux per square meter.

I have a specification that requires testing for 54 lm/m[sup]2[/sup] (5 lm/sqft). The referenced 5 lm/sqft doesn't make sense to me.

Could someone please clairify this for me?

Note: I posted this in the Computer Programs forum by mistake. Please ignore that one.

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
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[Maui]

MadMango, the following link may be illuminating.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/areance.html#c1

Maui

 

[MadMango]

From the General Computer Engineering Programs Discussion forum:

Why doesn't it make sense? What's the conversion from ft^2 to m^2

I thought if we were talking metric units it should be displayed as lux/m[sup]2[/sup].

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[MadMango]

not sure excatly what the question is but
54 lm/m2 is approx = to 5 lm/sqft
(1 m2 = 10.76 ft2)

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[DRWeig]

MadMango,

I think that Lumens, Footcandles, and Lux escaped unscathed from the metric versus imperial units war. Lumens has become kinda universal, even in places where area is measured in square meters.

You're on the right path, looking for about 5 footcandles. What's the application, by the way?

Your pal,

Old Dave

 

[MadMango]

Trying to comply with Federal Motor Vehicle Saftey Standards (FMVSS). I have a requirement to illuminate a platform and I am just double checking data from a 3rd party.

The spec reads "... provide at least 54 lm/m[sup]2[/sup] (5 lm/sqft) of luminance on all portions of the surface of the platform..."

My data reads simply "86 lumens @ X, 54 lumens @ Y, and 56 lumens @ Z." The platform is 12.75 sqft, so my thinking was I had to divide the posted lumens by 12.75 to give me how many lm/sqft I had. This is where my confusion is. Maybe I don't have to.

[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[IRstuff]

That's a trickily worded spec.

Does it mean that you must verify that each sqft of the platform receives 5 lm? or is a simple aggregate 12.75 sqft*5 lm/sqft sufficient?

TTFN

 

[IRstuff]

Note the phrase "on all portions of the surface"

This implies that you must be able to measure at least 5 lm/sqft at any point on the platform.

TTFN

 

[MilanK]

My book tells me:
1 lumen = 7.958e-2 spherical candle power
1 lumen/sq.ft = 1 foot-candle
1 lumen/sq.ft = 10.76 lumen/sq.meter
1 lux = 9.29e-2 foot candles.
It almost appears to me that the specifications dictate different illumination levels at different places of the platform. This can have its reasons so I suggest to contact the responsible person with the questions. Usually, the levels of illumination given are ment as minimal. But verification is prudent.

 

[DRWeig]

Geez, MadMango,

Can you infer the light level from the purpose of the platform? 54 lm/sq meter is a little brighter than a mall parking lot at night time.

In any event, your light source will be lossy, so the data you quoted probably is net output in the three planes. And yes, you'll have to divide your total lumen output by the square footage (or square meterage) to arrive at the illumination level. You'll need about 65 lumens spread as evenly as you can across the surface. Since your surface is small, it won't have huge variances. Your light source from which you quote data might do the job, but then again it might not. Hard to tell without seeing the distribution diagram and setup of your platform....

Or, if you can't experiment, ask the luminaire manufacturer to do a point-by-point calculation for you. They do it all the time.

Let us know how it turns out!

Old Dave