Re: [Phys-l] Hewitt's three answers

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2012, Mar 28, , at 15:59, Bernard Cleyet wrote:

cut

> I'll refer to my optics tome that give numbers to this when I return from Pete's coffee.
>
> bc used the "flicker" of a 7.5 W incandescent to set the speed of his high end turntable before he became very hearing challenged..

Some elision and paraphrasing  (pp. 202 ff.  Levi, Applied Optics)

"When lamps are operated on alternating current, the lamp intensity fluctuates at twice the frequency of the current. [duh]  The thermal inertia .... may reduce the fluctuations considerably. [duh]  
	The total variation in brightness as a fraction of the mean value can be approximated by a function of the filament diameter (W's mass - duh].  It has been given by


		m* = 0.0069 D^-1.06  for a 60-Hz supply,  
			....					25-Hz supply   

for gas filled lamps , and by

		 = 0.0056 D^-1.37   60-Hz supply etc.

for vacuum filled lamps.  [joke] D in mm.  

The modulation is a function of the wavelength --- [duh]   etc.etc.  i.e. much more.

bc  has THE book in his extensive library, and still has some memory.

p.s. for 6-V lamps, the initial brightness over shoots the equilibrium value by as much as 10%.   (The reason is obvious.)