APPENDIX 



VARIOUS UNITS USED IN THE 

 MEASUREMENT OF PHOTOSYNTHESIS 



Measurement of light energy 



The lux or metre candle is the illumination on a surface 

 normal to the direction of light and i metre away from a 

 point source of i candle-power. 



I foot-candle= 10-764 lux 



Approximately a tungsten lamp gives an intensity of 2 lux 

 per watt at a distance of i metre. 



The total energy flux is measured using a thermopile or 

 bolometer. It may be compared with that emitted by a 

 'black body' the total radiation from which at temperature 

 T° Absolute=5-67 iq-^ T^ ergs/sec./cm.^. 



The following units of energy may be used: — 



I gram calorie/sec.=4- 185 joules/sec. =4- 185 watts 



=4-185 10^ ergs/sec. 



Wavelength of light may be expressed as: — 



I Angstrom (A)=io~im^a=io~^ cm. 



The energy associated with one quantum of radiation is 

 given by 



he 



where h Planck's constant=6-62 lo"^? ergs/sec. 

 c velocity of light=2-99 10^^ cm./sec. 

 A wavelength in cm. 



Approximately a tungsten lamp has total radiation equiva- 

 lent to 60 ergs/cm. Vsec/lux. About 9% of this energy is at 

 wavelengths less than 7,000 A so that the visible radiation is 

 approximately 5 ergs/cm. ysec./lux. 



150 



