Photogenic Professional Lighting PLR1000DR User Manual download pdf (Page 11)

power point is commonly used in engineering and serves the purpose of

reporting the bandwidth of the flash duration, but the graph below clearly shows

that a power point measurement does not truly report the total flash duration.

The clock doesn’t start running until the flash discharge reaches 50% of its peak,

and stops when it falls below 50%. Since the color temperature of the flash

varies over time (more blue in the beginning and more red towards the tail [pgs

48-60]), it is important that flash duration be reported at the 1/10 power levels to

express the total flash duration and not cut off any of the available flash power.

Flash Duration

0.5

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Time

Intensity

t=1/2 Power Duration

Total Flash Duration (t=1/10)

You can see that there is quite a bit of light which would be wasted, if we set our

shutter speed to the duration using the t = 1/2 technique. In effect, the flash

duration is longer than you think it is — up to three times longer. So t= 1/2 or t

= 1/3 are not really useful measurements, since we’re used to thinking in terms

of shutter speeds. We at Photogenic want you to get consistent and constant

color temperature and all the flash power you paid for. That’s why we report all

Solair flash durations using the t=1/10 technique. As you can see, setting your

shutter speed to the t=0.1 flash duration or greater will result in your camera

capturing virtually all of the light available.

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Photogenic Professional Lighting PLR1000DR User Manual Page 11