Classroom Lighting is often too bright
Lighting in classrooms and offices is often very bright. This is partly because the room lights are left on unnecessarily, and partly because window blinds are often not used. In a recent survey more than 35% of classrooms had lighting levels that exceeded the level at which reading starts to become uncomfortable (1000Lux). It is good practice to ensure that ceiling lights are turned off when not needed and to use the window blinds to prevent direct sunlight entering the classroom.
How you can check using a camera
To determine whether the lighting levels are appropriate, you can take a single lens reflex camera and direct it at a page of text on the desk. The lighting is at recommended levels when the exposure is appropriate for a film speed of 100 ASA, an aperture of 5.6 and a shutter speed of 1/25th. More than this and the lighting levels are unnecessarily bright.
More than 80% of classrooms still have the old fashioned form of fluorescent lighting, in which the lamps flicker 100 times per second. This lighting is unhealthy: it can cause headaches and eyestrain and the flicker interferes with visual tasks.
Eliminate the Flicker
Next time the lighting in your school or office is changed make sure that the new form of high frequency electronic circuitry is used to control the lamps. This eliminates the 100 per second flicker and although the installation costs are higher, the lower running costs offset the additional installation costs in about two years. High frequency electronic circuitry can readily be obtained from conventional suppliers. Some circuitry has the additional advantage that it can enable the lighting to be dimmed.
These notes are taken from the page on lighting in Crossbow Education’s Visual Stress Assessment Pack, which contains lots of background information as well as how to conduct a test for choosing the correct coloured overlay.
I remember an afternoon when I was still teaching: it was a difficult, noisy class of 13-14 year olds. Someone asked if I could switch off the lights and pull down the blinds. I resisted, because I was suspicious of the motives of the person who made the request. However I acquiesced eventually. The tension leaving the room was like air escaping from a balloon. A lot of children in that class had difficulties with reading and writing, and they were the ones, usually, who were the source of the disruptive behaviour that often occurred. If I had known then what I know now I would have switched those lights of a lot earlier, and a lot more often!