can be used as the detection head in the UV detector and automatic free extinguish system. 

    Typical operating theory of UV light photosensitive diode:
    The UV light photosensitive diode has 2 symmertically designed electrode of a pure metal.when photons of sufficient energy range of 190-260nm stricke the negatively charged electrode(cathode),electrons will be emitted from it.If at that moment sufficiently high voltage is present these free electrodes will be accelerated in the direction of the positive electrode and in their path of travel through the gaseous atmosphere will ionize the gas,thus producing a gas discharge.This event causes the tube to become conductive as long as the voltage during the half period under consideration is above the quenching voltage for the discharge.
   The UV light photosensitive diode will stop firing once the voltage drops belong that level and fire again(if UV photons are still present)or the next half period.  

Type	spectrum  response	peak wavelength	igniting  voltage (Max)	tube voltage potential  drop	operating  voltage	operating current	sensitivity (Min)	background  current(Max)	Diameter	height
GD-18	190-290nm	210nm	260VDC	<210VAC	220±10%DC	2mAr.m.s	20cps	10cpm	29±1mm	29±1mm
GD-19	190-290nm	210nm	550VAC	500VAC	700AC	10mAr.m.s	20cps	0.2cps	28±2mm	28±2mm
GD-34	160-260nm	195±5nm	450VDC	330VDC	525±25V	0.3mAr.m.s	20cps	0.2cps	15mm	34±2mm
GD-35	185-260nm	210±5nm	260VDC	220V	300-350VDC	0.3mAr.m.s	20cps	6cpm	14mm	34±2mm
GD-708	185-280nm	200-210nm	185VAC	200VAC	220±10%VAC				19mm	31±2mm