Recently the office building owner retro-fitted all floors with energy efficient globes and sensor switches. The morning after they had done my floor I walked in and wondered if I had somehow lost my sight on the elevator ride up.
After determining that my eyes were fine but the globes were not, I asked our Safety Manager if there was a minimum standard of lighting under OSHA (Occupational Safety & Health Administration). This is America so of course there is! There is a table for various areas under OSHA 1926.56 MINIMUM ILLUMINATION INTENSITIES IN FOOT-CANDLES
The minimum illumination for offices is 30 foot-candles. The safety guy brought his snazzy little reader out and laid it on my desk. It showed the dim number of 14 foot-candles – in the poor lighting it was actually difficult to read that number on his gauge!
In case you are now wondering what a foot-candle is …… well, one foot-candle is the illuminance at a point on a surface which is one foot from, and perpendicular to, a uniform point source of one candela. (For those in metric one lux is the illuminance at the same point at a distance of 1 meter from the source). One lumen uniformly distributed over one square foot of surface provides an illumination of 1 foot-candle.
1 foot-candle = 1 lumen/square ft. I lux = 1 lumen/square metre.
So……… foot-candle is a measurement of light at an illuminated object and Lumens are a metric equivalent to foot-candles. It is difficult to measure room illumination more accurately than ±10% so usually one foot-candle is considered to be about 10 lux.
Once it was determined without a doubt that I was getting fewer foot-candles than acceptable I sent an email to our building manager drawing attention to the OSHA standards. Within 20 minutes the building engineer was putting my old globes back. I now have 38 foot-candles – whilst I am happy to help save the planet I'm not prepared to do it at the expense of my sight!
This is my desk - no flash on the camera.