When we think about what to do to improve the energy efficiency of existing buildings, the issue of improving the lighting is usually on the list of items to consider. But the idea that we might improve the daylight significantly is rarely on the list. I think that this is partially because it is a difficult concept to sell. There is no marketing campaign for natural light, there are few products that could be said to benefit from such a campaign if it did exist, apart from glazing manufacturers. How do we measure the impact of daylight versus artificial light in design and use of our homes. What can we do to improve the amount of daylight that we experience, and thereby reduce the amount of artificial light we use. The idea that we can and should improve on the amount of insulation in order to reduce the heat we lose is well understood, and there are many products in this sector, but there are very few to tell us that natural light can also save us money and can bring other benefits in the form of better long term health. The Daylight site has some presentations on the health implications of daylight exposure, which I found very educational. Usually the only time we hear about daylight and health in the same sentence is where some unusual circumstance has reduced a persons exposure to daylight and resulted in serious health problems. Some of these papers indicate that the lack of daylight exposure is having health impacts on children who play too little out of doors and on older people who are simply housebound. Although this is a phenomenon that has been discovered fairly recently, it is likely to have a serious impact on the design standards of some types of accommodation. It may lead us to consider how to allow daylight exposure to occur in more parts of the plans of our buildings than we have considered up to now. This in turn may lead us to reconsider appropriate ceiling heights for many types of building. It may even lead us to rethink the design of window systems to give us more control over the quality of light we allow into our homes. Whatever the outcome, it can only lead to improvements in design thinking and better health and happiness for building occupiers.