# Reading Irradiance from a light meter

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Thread starter 1 year ago
#1
Hi, I'm studying physics and was wondering about the light meter I used. It was set to 2000 so I could get readings, instead of 2 because the readings wouldn't show. Does this mean my values I get from the light meter is in mLux (milli) or just Lux?

Many Thanks
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1 year ago
#2
Should still be Lux, if I'm hearing you right it would only have reduced the precision of the measurement but would still display the same magnitude
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Thread starter 1 year ago
#3
(Original post by Sataris)
Should still be Lux, if I'm hearing you right it would only have reduced the precision of the measurement but would still display the same magnitude
Thank you, would the scale reading uncertainty therefore be ±1 lux?
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1 year ago
#4
(Original post by ottersandseals1)
Thank you, would the scale reading uncertainty therefore be ±1 lux?
If the best it could do was like "9274" at that setting, yeah
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Thread starter 1 year ago
#5
(Original post by Sataris)
If the best it could do was like "9274" at that setting, yeah
I got readings like 783, would this be acceptable for ±1 lux?
Last edited by ottersandseals1; 1 year ago
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1 year ago
#6
(Original post by ottersandseals1)
I got readings like 783, would this be acceptable for ±1 lux?
Yes that's the right error
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Thread starter 1 year ago
#7
(Original post by Sataris)
Yes that's the right error
Thank you so much. If I calculate the gradient of irradiance (lux) and square of the distance (m^-2) to find the constant. What would the unit of the irradiance calculated using a distance be?

It may sound like a stupid question, but I just wanted to make sure.
Last edited by ottersandseals1; 1 year ago
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1 year ago
#8
(Original post by ottersandseals1)
Thank you so much. If I calculate the gradient of irradiance (lux) and square of the distance (m^-2) to find the constant. What would the unit of the irradiance calculated using a distance be?
The gradient is rise over run, so assuming you plot lux against m^2, its units are lx/m^2 or lx m^-2
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Thread starter 1 year ago
#9
(Original post by Sataris)
The gradient is rise over run, so assuming you plot lux against m^2, its units are lx/m^2 or lx m^-2
For the distance on the x-axis, did you mean the unit to be m^-2. As in 1/d^2
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1 year ago
#10
(Original post by ottersandseals1)
For the distance on the x-axis, did you mean the unit to be m^-2. As in 1/d^2
Are you plotting distance squared or 1 over distance squared?
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Thread starter 1 year ago
#11
(Original post by Sataris)
Are you plotting distance squared or 1 over distance squared?
1 over distance squared. Trying to get a straight line through the origin
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1 year ago
#12
(Original post by ottersandseals1)
1 over distance squared. Trying to get a straight line through the origin
In that case the gradient would be lx m^2
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Thread starter 1 year ago
#13
(Original post by Sataris)
In that case the gradient would be lx m^2
Is it good practice to include this unit in my constant (gradient) or does it not matter?
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1 year ago
#14
(Original post by ottersandseals1)
Is it good practice to include this unit in my constant (gradient) or does it not matter?
You need to include it because the gradient does have dimension. Without the units it's a bit meaningless, as if you said a piece of string was "5 long"
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Thread starter 1 year ago
#15
(Original post by Sataris)
You need to include it because the gradient does have dimension. Without the units it's a bit meaningless, as if you said a piece of string was "5 long"
I aiming to investigate the inverse square law of a laser. What would be a suitable conclusion assuming the line of the graph of irradiance against distance squared is passing through the origin?
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1 year ago
#16
(Original post by ottersandseals1)
I aiming to investigate the inverse square law of a laser. What would be a suitable conclusion assuming the line of the graph of irradiance against distance squared is passing through the origin?
At the origin, 1/d^2 is zero. What does that tell you about the value of d at the origin?
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Thread starter 1 year ago
#17
(Original post by Sataris)
At the origin, 1/d^2 is zero. What does that tell you about the value of d at the origin?
It is zero. So they are inversely proportional?
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1 year ago
#18
(Original post by ottersandseals1)
It is zero. So they are inversely proportional?
d must be infinite for the illuminance to equal zero (at the origin). But yes, the straight line shows illuminance is inversely proportional to the square of distance
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Thread starter 1 year ago
#19
(Original post by Sataris)
d must be infinite for the illuminance to equal zero (at the origin). But yes, the straight line shows illuminance is inversely proportional to the square of distance
And that is a sufficient conclusion to my aim?
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1 year ago
#20
(Original post by ottersandseals1)
And that is a sufficient conclusion to my aim?
Yes, it sounds like you have verified the inverse square law
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