Measuring the hormone levels of students at a university in Sweden, researchers found that the students’ level of cortisol, the hormone that keeps us awake, increased in LED-lit environments with luminance levels of 100cd/m2. The work was based on a previous study from 2009, conducted with fluorescent T5 luminaires, which showed that the cortisol in students’ blood level increased when they were exposed to boosts of a high luminance in the morning and early afternoon.
Henrik Clausen, director of the Fagerhult Lighting Academy, said: ‘People started asking whether LED would have the same effect as T5, so we had to repeat our research. We did that at a school in Sweden where we found the same hormone release results.’ Clausen added, ‘Actually the pupils’ cortisol levels raised a little bit faster with LEDs than they did with fluorescent. It’s probably because there is an inherent peak of blue light in LEDs, but we don’t know that for sure.’
The research facility is now looking at students’ grades to see if the improved hormone levels result in better academic performance, but has not yet proven a correlation in the LED-lit classrooms. The 2009 study on increased fluorescent light levels showed an increase in performance by one grade on average in the dark part of the year, Clausen claimed.
Another study from 2007, also comparing differently lit classrooms, showed that colour temperature did not make a difference to the students’ hormone levels, whereas light intensity did.
Speaking at the International Lighting Fixture Design conference in London last week, Clausen cautioned not to apply the research results too widely: ‘If you want to do research you have to choose a path and we chose to focus on classroom lighting, so we don’t claim that this approach works for everything.’