Cornell University Ergonomics Web
Lighting Visbility Calculator
As the workforce ages there is a need for greater light levels on paper
documents in offices, while at the same time for computer screen work there is a
desire for lower light levels.
This XL worksheet provides a calculator that estimates the illuminance
required on a target to achieve the same visibility for people of different
ages. You input the measured light level into the worksheet, and if then
estimates the required light level for equivalent visibility for people of
different ages and tasks requiring different visual demands. The estimated
equivalent light levels are based on data on the increase in the optical density
of structures in the eye as a person ages.
Use the visibility calculator to help you choose the an appropriate light
level (illuminance) for a person and the work they are doing.
Download the Cornell Visibility Calculator
Some Q&A's about the calculator
- Q. What about the illumination plane. In the home few people perform
tasks in the horizontal plane; appliance controls are usually in the
vertical plane as are the recesses of cupboards?
- A. Actually the plane shouldn't matter because the idea is to put an
illuminance meter at the target, whether horizontal or vertical, so
everything indexes to the light meter reading not the light source or
direction.
- Q. What are the implications of the square law?
- A. The calculator assume a normal viewing distance range over which the
inverse square law will have a negligible effect.
- Q. What's the effect of ambient and task lighting?
- A. The type of light source doesn't affect the calculations because
everything indexes to the light level at the target, whether that's achieved
by natural, ambient or task lighting. Of course, the calculator doesn't take
into account possible spectral issues with light sources and targets, but
then neither do our lighting standards!
people have downloaded this evaluation form.