clive rayner wrote:

Hi

I am struggling to understand where the figures in the above sample calculation step 1 are derived. I can see that 610/457.2 ^1.641 = 1.60506

but

12,670/8286^1.641= 2.009.

Can anyone help me understand where these figures are derived

thanks

The information shown is for adjusting the incident energy from the normalized working distance of 24 inches (610 mm) to your distance of 18 inches (457) mm.

The adjustment is based on the ratio of the two distances raised to the exponent of 1.641 The theoretical exponent was traditionally “2” but IEEE testing shows that this value varies depending on equipment type. 1.641 is for a panel.

The basic concept is the incident energy decreases exponentially with increasing distance. It also increases exponentially as the distance decreases.

As far as the calculations, here is what I have:

(610/457.2)^1.641 = 1.605

Or as IEEE has it in their equations:

(610^1.641) / ( 457.2^1.641)

37215.7 / 23,186.5 = 1.605

The result of 1.605 means that the incident energy will increase by a factor of 1.605 when a person moves from the normalized distance of 24 inches to a working distance of 18 inches.

Hope this helps.