Measure LUMENS in a room

[bobobano]

Greetings,

For my degree project I'm controlling the light in a room as the outdoor light increases and decreases, I'm having an issue calculating the amount of lumens I'm actually measuring and I'm hoping someone hear can help clear it up.

Using the formula from the datasheet of the LDR Ladyada provided:
http://pdf1.alldatasheet.com/datasheet- ... P8001.html

Log(R100)-log(R10) / log(L100) - log(L10) = 0.6

And this is the first issue I have, shouldn't that be an inverse relationship? (ie -0.6)

I know that lumens can be found by lux*Sa, and for these LDRs I calculated it to be L = lux*2.188x10^-6

So i rearranged the equation to be

Log(R@100/R@10) = log(L@100/L@10)^0.6
R@100 = R@10*(L@100/L@10)^0.6

Pluging in the given R@10 and L@10 (and calculated L@100)

I get R = lumen^0.6 * 6.37x10^-3 * (3K to 11K)

A linear relationship. And thus, the cause of my problems, a linear relationship which I don't believe I should be getting. Help me Obi-Wan Kenobi, you're my only hope.

[zener]

I think Luxeon has some decent app notes on this subject. If you are measuring light falling on a surface that is lux. Light out of an emitter is lumens. Are you trying to figure the lumens you will need to achieve a certain lux? That is not so important for control, you just need to know "higher or lower".