Intensity
To be effective, a visual signal (or its reflection from adjacent walls and ceiling) must be of an intensity that will raise the overall light level sharply, but not be so intense as to be unsafe for direct viewing when installed at a specified mounting height. Lamp intensity is given in effective candela (cd), measured in use at the source. In research testing, 90% of subjects were alerted by a 75 cd signal mounted 50 feet away on the wall directly behind them.
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