vray light meter

[val2]

Do the vray light meter numbers represent candelas? if not what do they represent?

I have a report saying it needs to have a room with no less than 25 foot-candles on a clear sunny day. my understanding of a foot-candle is the illumination from a candela source a foot away.

the room I have made has a series of windows and a sky light and the numbers from the vray light meter are from 4000 to 10,000 so I was wondering what the 4000 to 10,000 meant.

Just seems like a crazy low number, 25 foot-candles, if we are talking about the sun bouncing around in a room, but I'm probably missing something.



thanks

Val

[val2]

so, after doing a little more searching in the forum it seems that the measurement is in LUX (correct?) and after looking on line one footcandle is 10.764lx The formulas on line are well above my pay grade but they do have calculators. I was wondering how one might decide the measuring distance from a skylight well. from the window opening or the opening of the well? (they ask for the measuring distance to to calculate Candelas)

[val2]

I thought I would back up a little. I set up a scene in meters (I normally use feet) I created a vray light plane 1 meter square and placed it i meter above the vraylightmeter (1 meter square). I put it in a shelled box to be safe. I gave it a default value of 1 so a luminous value of 1499.701lm (477.465lm/m?) (the vray light meter gives a hotspot value (the highest number) of 489.4.
what I don't understand is the relationship between the two numbers. If 489.4 illuminance is LUX (yes?) then how does it relate to the number 1499.701? what is the calculation?

I went to a site for calculations and lumen/square meter (lm/m^2) and lux is the same number out that I put in. so what is the difference of 11.935?

[vlado]

so, after doing a little more searching in the forum it seems that the measurement is in LUX (correct?)

This is correct, yes.

I thought I would back up a little. I set up a scene in meters (I normally use feet)

Are both the system units and the display units meters?

I created a vray light plane 1 meter square and placed it i meter above the vraylightmeter (1 meter square). I put it in a shelled box to be safe. I gave it a default value of 1 so a luminous value of 1499.701lm (477.465lm/m?) (the vray light meter gives a hotspot value (the highest number) of 489.4. Qhat I don't understand is the relationship between the two numbers. If 489.4 illuminance is LUX (yes?) then how does it relate to the number 1499.701? what is the calculation?

The light power is the total amount of light emitted by the light source (in this case, 1499.701 lm). This light is distributed throughout the entire scene; some of it will reach the light meter, and some of the light will not. The light meter measures the amount of light reaching the grid points on its surface in lx (lm/m^2). This amount depends on the shape of the light source and its distance from the measured point. The relationship is complex and involves integrating the rendering equation at the particular grid point.

Best regards,
Vlado

[val2]

Yes both the system and the display are meters.

I think I may have it now. what was throwing me was the large numbers before. I was reading the paper that said a minimum of 25 footcandles were need in the room and I was trying to figure out what the numbers represented. I found a site that does a conversion from lux to footcandles http://www.unitconversion.org/unit_c...umination.html It says that 25foot candles work out to 269 lm/m^2 (does this sound right?) so as long as the conversion is right I can fiddle with the skylights to get an appropriate size

yes I imagine the calculations are complex and way over my head.

thanks

Val