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
In many schools, classrooms can have excessive lighting installed, particularly in corridors. This is often arranged so that individual rows or areas of light fittings can be switched on and off separately. This monitoring exercise will help you to identify those lights which do not need to be switched on under normal daylight, and to implement a programme to ensure they remain switched off.
Aim of the investigation
To find out light levels in classrooms and corridors, and identify whether energy use on lighting could be reduced.
A cheap light sensor (LUX meter) to record light levels.
A spreadsheet or results table to record your results.
- Choose a day with average levels of daylight (i.e. overcast day/not too sunny).
- Design a spreadsheet or results table to record your results. You will need to record the classroom or area of the school, whether the lights are on in the classroom, whether the blinds are down, and at least 3 different light level readings in different areas of the classroom or corridor.
- Record the light levels using the LUX meter in each room or area of the school when you first enter it. In classrooms record the light levels at desk height in at least 3 different areas of the room including the area furthest from the windows.
- If blinds are closed or windows obscured by resources, record this in your spreadsheet or results table.
- If the lights are on, record this in your spreadsheet or results table.
- Switch off any lights and open the blinds. Record the light levels again. Do they meet the recommended lux levels for schools.
- If not, start furthest from the window, and switch each row of lights back on one at a time if possible. Each time measure whether there is an adequate amount of light to work effectively at desk level in all areas of the room.
- When you record an acceptable amount of light in the room, stop switching.
- In consultation with the class teachers in these rooms, discuss your findings and get their agreement as to which rows of lights could normally be left switched off.
- Once identified, mark up the respective switches with red stickers in order to indicate to the staff and pupils that these marked switches are not to be used unless necessary (i.e. at night, on a very overcast day, or if a pupil needs more lights on).
- You could also use green stickers for lights/switches that should be used as needed. Red Dots – Do not touch and do not use (override this as necessary at teachers’ discretion) Green Dots – Switch and use lights as required
- The actual light levels from natural daylight can vary greatly due to the cloud cover and position of the sun. Consider repeating this monitoring exercise at different times of day, and under different weather conditions. Record the outdoor light levels before you start each episode of indoor monitoring.
Data Analysis and Presentation
- Calculate mean lux levels across your school before your lighting adjustments.
- Plot a chart showing the mean lux level in each classroom or area that you monitored before and after your lighting adjustments.
- Rank each classroom or area of your school by its mean lux level before your lighting adjustments. If you repeat the monitoring exercise at different times of day, does your ranking list change significantly as the sun moves around the buildings?
- Create a way to highlight the classrooms or areas of the school where artificial light is used unnecessarily.
What do your results tell you about pupil and staff behaviour with regard to switching on lights unnecessarily? Give your evidence for your conclusion. How can you use the information you have learnt to save energy?
Next Steps to save energy
- 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.
- Consider asking your school management team to remove some of the light bulbs from their fittings in over lit areas of the school.
- Ask your school management team to 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.
- Ask your school management team to 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%. Adjusting the artificial lighting according to the amount of natural light in a room using daylight sensors or photocells can reduce electricity use by up to 40%.
- Discuss with your school management team 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 2–3 years.
- When possible, position computers in classrooms so that they are parallel to the window wall, their monitors face a blank wall, and there are no windows behind the user. This means natural light can be used more often without glare problems.
Evaluate how you carried out the investigation and what could be improved.
- Introduce a regular monitoring activity to ensure your school makes the best use of natural light, and avoids switching on artificial light unnecessarily.