regularguy

Jose

The calculations are a bit hard to figure out but i will demonstrate how you cant get a higher footcandle reading from the meter than what the lumen rating of the bulb is. This is theoretical because reflectors wont bounce all the the lumens into the area you want to cover perfectly.

Here is the equation for illumanince. I=L/A
I=illuminance
L=lumen output of bulb
A=4pid^2=surface area of sphere you are lighting


I=8900/4pi=708 ft candles

Now if you go farther away footcandles get smaller.
I=8900/4pi*4=177 foot candles at 2 feet

And closer
I=8900/4pi*.25=2832 foot candles

And even closer at 1 inch
I=8900/4pi*(.0833^2)=101986 footcandles

And if you built a perfect reflector you would be able to get half of the sphere projected where the other one is in effect doubling the usable footcandles. but that wont happen and you might be able to get 80% in real life. So no the lumens dont double with a reflector but the footcandles would. And so would the usable photon energy. That is a good thing.

And of course, this is the reason plants start to look like **** when grown on flouros. They dont have enough light to penatrate the whole plant and the bottom leaves die. Hence the need for sea of green and whatnot.