Switched off lights on sunny days

Optimise use of natural window light to positively affect mood, energy and concentration and save energy used by electric lights

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Overview

Introduction
Natural window light has long been known to positively affect mood, energy and concentration. However, a familiar scene in classrooms and offices is the use of blinds to control glare when it is bright outside. This is particularly common when whiteboards and projectors are being used, as many models are not bright enough to view in strong natural daylight. Often the blinds are left drawn, with lights switched on, even when the whiteboard or projector is switched off. 

Where possible, staff and pupils should be encouraged to use blinds to direct daylight onto the ceiling and walls instead of closing them completely. This should reduce the need for electric lighting in the classroom whilst reducing glare.

Another common problem in schools is windows partially obscured by resources and displays. Keeping windows clear helps to optimise the amount of natural light entering a room. 

The lux is the standard unit for measuring light. It is equal to one lumen per square metre.
The recommended lux levels for schools are:

Corridors: 100 lux
Foyers, entrance halls, canteens: 200 lux
Libraries, sports halls, gyms, classrooms, computer rooms: 300 lux
Laboratories, kitchens: 500 lux
Technical drawing room: 750 lux

Consider purchasing a cheap light sensor (LUX meter) to record light levels across the school, and then take action to maximise natural daylight and minimise energy waste.

Next steps to save energy
  1. Create an action plan to target those areas of the school with higher than average lux and artificial light use. Design some posters to encourage staff and pupils to open the blinds and switch off lights. 
  2. Create a maintenance schedule which includes:
    • Cleaning windows, skylights and fittings
    • Checking and replacing old and dim lamps
    • Ensuring controls are in good order and set properly
    • Cleaning occupancy sensors, if installed. Without regular maintenance, light levels can fall by 30% in two to three years.
  3. When possible, position computers in classrooms so that they are parallel to the window wall. Monitors should face a blank wall and there should be no windows behind the user.
  4. Remove some of the light bulbs from their fittings in over-lit areas of the school.
  5. Choose the most efficient lighting possible. Upgrade existing light bulbs and fluorescent tubes to low energy LED tubes and lights. LED lighting reduces energy use and heat output, eliminates flicker and hum, extends lamp life (by up to 50%) and can allow dimming – all of which can make a classroom more comfortable. Make sure this happens by asking the school management team to include it in the school’s purchasing policy.
  6. Consider occupancy and daylight sensors in problematic areas of the school. By dimming or switching off lighting when there is nobody in a room, occupancy sensors can reduce electricity use by 30%. Using daylight sensors or photocells to adjust the artificial lighting according to the amount of natural light in the room can reduce electricity use by up to 40%.

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