Light
What is a 'foot-candle'? - this is a light unit which can be measured with a light meter. However, if you do not have a light meter to hand, there are methods of roughly estimating how much light your plants are receiving.
If you use the shadow cast by your hand 30 cms above a leaf:
Sharply defined edges to the shadow would indicate a light intensity of over 5,000 foot-candles.
If the shape of the hand can be defined but the edges of the shadow are blurred, then that might indicate a light intensity of over 2,000 foot-candles.
If the shadow can be detected, but there is no outline to suggest what is causing the shadow, then the light is likely to be under 1,000 foot-candles.