while embodiments of this invention can take many different forms , specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention , as well as the best mode of practicing same , and is not intended to limit the invention to the specific embodiment illustrated . in an embodiment of the invention , monitoring of output of a source light emitting diode ( led ) can be implemented by measuring reflected or scattered light from a lens that is used to focus the led light into a smoke chamber . the reflected light can be used to both control the optical intensity of the led and to provide feedback as to the led &# 39 ; s optical output intensity . in one aspect , the drive circuit for the led employs a photo diode to provide feedback . some of the light from the led is reflected off the lens . an optical sensor , such as a photo diode detects the reflected light . the current produced by the photo diode can be used to provide feedback to a driver amplifier for the led to maintain the optical output power at a predetermined level . in another aspect of the invention , the feedback circuit that is connected to the photo diode can also include a detection circuit . when feedback signal establishes that the led amplifier is in its linear region of operation , the detection circuit provides an output indicative of the led operating properly . when the feedback is no longer enough to maintain the led amplifier within its linear region , the detection circuit provides an output indicative of the led not working correctly ( for example , burned out , degraded excessively ). in response thereto , a maintenance or trouble signal can be generated . in another aspect of the invention , an aspiration unit , a fan or blower for example , can be coupled to the detector &# 39 ; s smoke chamber to inject fluid into or draw fluid from that chamber . that aspiration unit can be local to or remote the detector . control circuits can be coupled to the amplifier for the optical source , a sensor of reflected radiant energy therefrom and a smoke sensor associated with a sensing chamber of the respective detector . such circuits could be implemented with one or more programmable processors and associated control software pre - stored on a computer storage medium . fig1 illustrates an embodiment 10 of the present invention . detector 10 includes a housing 12 which carries a smoke chamber 14 . control circuits , generally indicated at 16 can also be carried by housing 12 . it will be understood that the circuitry configuration of fig1 is exemplary only . other circuit configurations come within the spirit and scope of the invention . circuitry 16 includes an optical amplifier 16 a which is coupled to a source light emitting diode 16 b . radiant energy 16 c emitted by led 16 b is directed toward a lens 18 . a focused portion 18 a is directed into the smoke chamber 14 and used to detect a smoke concentration therein . various configurations of smoke chambers are known to those of skill in the art and do not represent a limitation of the present invention . an optical smoke sensor 14 a , for example , a photo sensor , is coupled to chamber 14 and produces an electrical signal , on line 14 b indicative of smoke concentration in chamber 14 . radiant energy 18 b reflected off of lens 18 is indicative of radiant energy output from led 16 b and is received by photo sensor 16 d . sensor 16 d is coupled in parallel to a resistor 16 e . a voltage generated across the sensor / resistor combination 16 d , e can be fed back to amplifier 16 a so as to adjust an electrical input parameter of source led 16 b and to maintain the source 16 b operating in its linear range , assuming normal operation . that same voltage can be evaluated in a threshold establishing amplifier 16 f to generate a binary output status signal . a buffer amplifier 16 g can be used to intermittently activate source 16 b and sensor 16 d . it will also be understood that at least some of the above noted circuit elements could be incorporated into additional control circuitry 16 - 1 . control circuitry 16 - 1 could be implemented , at least in part , with one or more programmed processors 16 - 2 which execute control programs 16 - 3 pre - stored on a computer readable storage medium , for example eeprom . control circuitry 16 - 1 can also include a wired or wireless interface to communicate with a displaced monitoring system m via a medium 22 . smoke indicating signals , on the line 14 b can also be coupled to control circuits 16 - 1 for evaluation and transmission of indicia thereof to the monitoring system m . an aspirator 24 can be coupled to the smoke chamber 14 , to inject ambient air into the chamber or to draw it from the chamber , all without limitation . the aspirator 24 can operate under the control of circuits 16 - 1 . it will be understood that aspirator 24 can be carried by housing 12 , or , displaced from housing 12 all without limitation . neither the exact characteristics of the aspirator 24 nor its location are limitations of the invention . from the foregoing , it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention . it is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred . it is , of course , intended to cover by the appended claims all such modifications as fall within the scope of the claims .