dedolight PB70: breaking the square law

The dedolight PB70 is unique - not just in physical appearance, not just in terms of high output and low energy consumption: the PB70 enables the cinematographer to achieve a natural, organic quality of light while at the same time defeating what is called The Inverse Square Law.

In simple terms the inverse square law means “as distance increases from the lighting source intensity decreases.” When we double that distance from the light source the result is a quarter of the original light; however, when working with the PB70 this is not true.

The measurements below show photometrics from tests performed using the PB70 and the results achieved:

According to the Square Law double the distance = 1/4 of the light. The results above show at 5m the light intensity of the PB70 is 112,000 lux. Therefore at 10m (double the distance) the expected result would be 27,000 lux (a 1/4 of the light.) Yet the result is 68,000 lux.

The reason for the unexpected result, which goes completely against the Square Law, is that the dedolight PB70 is special. Due to the parabolic construction which results in an intense parallel beam, the light itself does not come from the light head, rather it comes from behind the light from what we call a virtual light source.

This concept is difficult to explain and understand: essentially, the virtual light source is 20m behind the light fixture which means the distance from light to subject, particularly when reflected, is dramatically increased.

The result is when the subject moves towards the light or away from the light, exposure changes are minimal. Anyone who has worked on a film set knows the square law jumps in at the worst moments, bringing limitations and exposure issues to the filming process. The dedolight PB70 by design and capability overcomes these issues.

Furthermore, the lighting quality is different, again the result of the light originating from way behind the lighthead. The dedolight PB70 is one of the few lights that can effectively simulate daylight and sunlight. This is due to the parallel beam which this light creates which is then reflected, further extending the path of the light. dedolight calls this Infinity Lighting: the illusion of natural light from a far distance. 

Watch the movie below demonstrating the concept of Infinity Lighting while showing many examples filmed using the dedolight PB70 and the dedolight Lightstream system:

dedolight products are available
in the UK through Cirrolite