I’ve been corresponding with Mike Shulman, Principal Engineer, Lighting at UL in Fremont California. My discussion focussed on a number of topics but let’s look at visibility in smoke.

I asked for Mike’s comment on this statement: A PLM exit sign does not work in smoke conditions and smoke is a foreseeable circumstance.

Mike’s response:

No exit signs work in smoke. Smoke creates two concurrent conditions: first, it scatters all light making any exit sign just a faintly glowing object with no discernible legend or image. Second, it is an extreme irritant to the human eye and makes it virtually impossible to keep your eyes open at all (resulting in no visibility whatsoever). Smoke filled rooms and hallways can generally only be traversed by getting very low to the ground where, for a period of time, the smoke layer may not be complete. Floor proximity luminous path markings are the preferred tool to assist with building evacuation where smoke is likely to occur during the process.

It’s interesting that the Lighting Cartel look to propose more and more luminance to solve a problem that could be solved very easily with a low level photoluminesent sign.