Angle of view of Fire Escape Signs

[CWEENG]

Afternoon Gents,,,

Asked the question recently by a client over a cup of coffee,,,

External illuminated sign viewing distance being 100 x its height of the legend,,,, ? Fine no problems with that?

Obviously looking strait at the sign it will give the best view, but in such building as large floor space factories you are never going to achieve a strait on angle to the sign from all locations (increasing the angle is going to decrease your view of the sign until it is non effective)

At what angle from strait on at the sign would the sign be non effective,
Is it on  sliding scale eg.. at 10 degrees decrees the distance by 10% etc? or other formula

[Owain]

It'll be cosign trigonometry. The actual formula escapes me.

[DavyFire]

Hi,
   BS5266-1:2011 states

Where the angle of viewing of the safety sign is not predominantly normal to the sign, the effect of angle of viewing should be taken into account, using the guidance in BS ISO 3864-1, and the factor of viewing distance reduced by a multiplying factor of cosine of the angle of viewing to the normal to the sign.

Sounds very complicated to us that left school a long time ago. Easier to fit a few more signs.  DF