Emergency lighting standards are in the spotlight after concerns have been raised about the effectiveness of the present illumination levels. Although a change to the human eye may take a long time to evolve, the way that society norms change occurs without anyone really noticing. And, by the law of unintended consequences, it looks as though we may have gone through just such a shift.
The thing that’s gone unnoticed is a small app in everyone’s smart phone – the flashlight. What hasn’t changed are the design illuminance levels for escape routes, typically 0.5 Lux – 1 Lux, and we may now be experiencing a mis-match between what is, and what isn’t, acceptable.
What the Standards assume is that, should the power fail in a building and we’re invited to make our way outside, then our eyes will adjust to the lower illuminance levels and we will then make our way outside in a calm and ordered fashion. What’s happening physiologically is that the eye is adapting from normal, photopic conditions to that half-light where objects become less clear and colours cannot easily be determined – mesopic vision.
The adaptation time from one to the other can take a few minutes; it may be here that the societal change is having an impact.
What may be happening is, rather than waiting through the adaptation period, there is an altogether different response; people are reaching for their mobile phones and immediately switching to the flashlight function, attempting to hold onto their photopic vision. For a single person in a room, that may be fine, but a crowd of people in the same situation brings visual chaos. The effect of contrast on the eye between a viewing a very bright source – the brilliance of the flashlight – while attempting to adapt to a very low general illuminance can be debilitating.
No one ever expected the general population to go around with torches in their pockets, but now that it appears to be the case, what happens next? Should emergency lighting standards be adjusted to a higher level to cope with this evolution in our social habits?
- A one-day Lux conference on Emergency Lighting takes place on Thursday 25 February at the Cavendish Conference Centre, London. Delegate places are free to facility managers, energy managers, consulting engineers and other independent specifiers. To register for a free place at the conference, click HERE.
Picture: Lux magazine