Re: [Phys-L] Making video content with incandescent light and 100Hz bands problem

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2012, May 13, , at 13:28, Derek Chirnside wrote:

> Any thoughts?  Is there maybe a simple way to phase shift the voltage
> powering one of the bulbs?  Or even do it to two other bulbs??
>
> -Derek


That's a thought, and very easily done.  Well, .. depends on the your domestic supply.   Nearly everywhere in the US 240V is supplied with three wires -- discussed interminably on phys-l.      the "middle" wire is grounded physically and spiritually.  its common as the "return" for the other two which must be Pi phased otherwise one wouldn't obtain 240 V.   So the prob. is connecting one lamp to one leg and tother tother.

I once wired a power fan out so adjacent sockets were alternate legs.  The sockets were spaced, so one could plug a plug in half of adjacent sockets to obtain 240V.  Or may be this was, more likely, a wall socket.



Now the question  dose this result in a constant illumination.  Ideally I think so.   the EMFs are sin(120Hz*2PI*t) and cos ....  the power is ^2  and cos^2 + sin^2 =1  However, the illumination is not proportional to the power, because the resistance is a function of the temperature.  However, I think it'll be a great improvement.  OTOH maybe this variation won't matter -- my brain hurts,  Furthermore, my thought before reading your ingenious soln. was to use a very heavy filament lamp in order to make use of its thermal inertia.  e.g. a 500 watter or cooler a 6V auto head lamp not Si-halide.  Finally, we here in Salinas have LED'd (~ 95%) our house.  I just used the fingers strobe, and found, as I suspected, they are fed w/ pulsating DC.  I also compared 15 W and 300 W incandescents.  Both flicker** w/ the 300 W noticeable less. And the LED, as expected, MUCH worse.   


**Applied Optics, Levi.:    M*  = 0.0069* D^ -1.06  M* is the variation about the mean illumination.  D is the filament diameter in mm.  (gas filled 60 Hz supply)

I've thought of getting a DC setup, but bulbs cost much more.  Like $27
rather than $2.
I've priced an LED option, this also is quite expensive, although there are
other options I suspect.

DC bulbs? What are they?***  How about the auto headlamp and auto batt.?   With a charger on line.  [I though AC because the ten lamps NPS surplussed included step down xformers.]


*** Two 12 V. bulbs supplied w/ my solar set up from Harbor freight -- three ~2X3' panels converter (12=> 120) / charger for the not supplied batt. and the two lamps.


Since LEDs are too expensive I wont suggest adding a filter to a coupala.    The 18 W   885 lumens I have appear demountable, but no, because would void the warrantee (v.~ $40)



bc too often a bit dim.