What is "good light?" The question of
proper light levels has been debated for over a century and continues
to generate heated discussions. The debate often boils down to one
issue: is brighter better? The answer seems to be: it depends.
The first users of electric light were accustomed to oil lamps
and candles. Some urban residents used gas lighting wherein a typical
gas jet produced about 16 candlepower. Thomas Edison deliberately
designed his new incandescent lamps to give 16 candles so as to
directly compete against gas, and this rating became a standard
for many years.
Sixteen candles roughly equates to the output of a modern 25-watt
lamp. Lamp makers throughout much of the twentieth century pushed
consumers to buy higher output lamps, arguing that low levels of
light created eyestrain as users struggled to read or perform other
tasks. Notice the child's drawing in this late 1920s blotter carrying
the caption, "I like lots of light." And indeed, objective
studies indicated that both productivity and safety increased with
higher light levels in the home and workplace.
By the 1970s "blankets of light" were commonly designed
into buildings as discharge lamps with ever higher output became
available; the "brighter is better" mantra reached a peak.
However, soaring energy costs in that decade sparked a reevaluation
of this policy as some engineers, designers and users began asking,
how much light is enough?
Research on this question continues in both corporate and academic
laboratories. Human eyesight changes as we age, and current research
indicates that an "adequate" light level for seniors can
be up to seven times higher than that considered "adequate"
by young people. Cultural factors can also play a role. For example,
one designer with offices in both countries noticed that light levels
in France were generally lower than in the U.S.
One result of the reevaluation is the growing design emphasis on
"task lighting." This refers to a practice of putting
higher levels of light where needed, such as a desktop, and less
light in other areas.
For additional information about light-levels and research on human
perception of light see:
- Illuminating Engineering Society of North America, IESNA
LIGHTING HANDBOOK, Ninth Edition, (New York, NY: IESNA Publications
- Lighting Research Center at the Rensselaer Polytechnic Institute:
- P.A. Aspinall and J. Dewar, "Lighting and perceived guilt" in
Lighting Research and Technology, 1980, V. 12, #3, p.140.
- M. Clay Belcher, "Cultural aspects of illuminance levels" in
Lighting Design and Applications, February 1985, p.49.
- Taylor Moore, "Human Performance in the Spotlight" in EPRI
Journal, September 1993, p.15.