Science Buddies: "Ask an Expert"

Hi

I'm confused about whether I should interpret 'mcd' as millicandela or meter candle. I'm going to put several 3pi led above 13cm of 13*13*13 box to culture Euglena and the internet says that they need 300 foot candles above 50cm. So I found out 3pi led and it says;

red: 170 mcd
white: 400 mcd
blue: 120 mcd

I don't know whether I should interpret this 'mcd' as millicandela or meter candle. I calculated how much led I need and it was;

1. if mcd=meter-candle

1 foot candle=10.764lux=10.764cd/m^2
300 foot candle=3229.2lux=3229.2mcd(meter-candle)

then I need 4 white led, 27 blue led and 19 red led.

2. if mcd=millicandela

1 foot candle=10.764lux=10.764cd/m^2
300 foot candle=3229.2lux

3229.2cd : 1m^2 = x cd : (0.13)^2m^2

x cd = 54.57348 cd = 54573.48 mcd

then I need 136 white led, 455 blue led, 321 red led.

Is my calculation right? And which one is right?

I would really appreciate if you answer it.

ahhanam - The conventional expression for 'mcd' is milli-candella. If you are thinking of meter-candle, the conversion is --> 1 meter-candle = 1 candela steradian/meter². I think the units here that you describe for the LED output is milli-candela. I don't understand your reference to '3pi LED'. It seems that you are trying to create a specific light spectrum made up of red, white and blue light emitting LED's. Understanding the specification sheets of the specific LED's you intend to use and the units of luminance involved you should be able to complete your experiment. Continue to search web information on luminance units to see how it coincides with the information in your experiment description.

Rick Marz