Andy: : I'd say in the build it yourself scheme ... avoid 110 or 220 like the : plague - you can get an unpleasant shock! . Use high intensity LEDs if : at all possible. These can be run from batteries. I don't know about : their output vs. drop in voltage but they consume little power and : should provide a fairly steady output. You can get them at Radio Shack. : You can also get a CdS photocell there. agree with Andy 100%, mains powered is unnecessary (so maybe my link was a bad choice!) You could cobble this together cheaply, easily and with greater safety using 1 9V battery . A voltage regulator circuit stabilizes the voltage so the power consumption is fixed and then the light output will remain to all intents and purposes - constant. let's see.. (heads to US radioshack website) whoah! hmm.. Radio shack prices are as ridiculous there as they are in Australia I see, but pushing on.. bits needed: http://www.radioshack.com/product/index.jsp?productId=2062599 1x 7805 voltage regulator IC http://www.radioshack.com/product/index.jsp?productId=3060980 1x 5mm white LED 25mA 3.3V http://www.radioshack.com/product/index.jsp?productId=2062590 1x CDs photoresistor (not used in this part of the circuit) http://www.radioshack.com/product/index.jsp?productId=2062314 1x 68 ohm (dropping) resistor http://www.radioshack.com/product/index.jsp?productId=2102510 1x 100µF 35V Electrolytic Capacitor http://www.radioshack.com/product/index.jsp?productId=2062365 0.1µF Ceramic Disc Capacitor this is your light source circuit, nice and safe and very stable :) switch ___ 68 ohm r \ | | +9VDC-- \-------------| A |------/\/\-- | |___| | | | | | _|_ | | | \ / LED _|_ | _|_ __V__ 100uF --- | --- | | | 0.1uF| | | | | | ___________|_____________|______|______| A= 7805 voltage regulator hope this helps : BTW, the calibrated Stouffer wedge may be expensive. I have not checked : price myself though. you could always ask around any of the local graphic degign places and see if they have one lying about - also remember that densitometers need to be calibrated each time they're used, though you'll find an LED model to be a lot more stable than an incandescent light source model karl
