It is interesting to consider how we truly define and measure the efficiency of artificial lighting as we continually strive to lower energy consumption. 

Here are some spectrometer readings: 

Evening Sunlight – The light that Homo sapiens have experienced before sleep for hundreds of thousand of years.

Firelight – The first ‘artificial’ light source that we ever used, followed by oil lamps, candles and other open-flame light sources. 

Incandescent light – The first widely used electric light source, creating a radical improvement in light quality across industrialised parts of the world for over 100 years.

It’s striking how similar incandescent light is to fire and to a light source that is so important for our well-being: sunlight. Incandescent light has a similarly ‘natural’ spectral distribution. 
 
Compare this to an example of a typical LED 4000K below—light we have been experiencing in interior and exterior spaces where we spend much of our time over the last decade or more.  

The LED source has a completely different distribution of light from the others. Significant parts of the red portion are missing to save energy and wasted heat, and there are noticeable spikes in the blue portion. The detrimental impacts of this at night, particularly the blue spike, on humans and our surrounding natural world are very well known. The negative impacts on humans during the day in offices, public spaces, and even healing spaces such as hospitals are varied and complex and are the subject of much ongoing research.  

Fluorescent lighting bridged the gap between incandescent and LED, but it also had its own deficiencies within the spectral distribution and associated health issues. 

We know that the biggest cost in most businesses is the workforce, according to the World Green Building Council (2014). The health and well-being of employees is key to a profitable company; sickness, absenteeism and mental well-being have a significant impact. The same could be said for a town, city, country, or planet if we save costs by generating as many lumens per watt as possible. Still, we end up with a quality of light that accelerates climate change ecologically and impairs human health globally, so is it really more efficient? 

It’s good to see more emerging light source technologies, such as Thrive from Bridgelux, that aspire to address this issue. Light sources like these strive to deliver a spectral distribution of light closer to daylight, along with a high CRI, while still achieving an efficacy well above 100lm/w.

The naturalness of these light sources can now be quantified using the Average Spectral Difference unit of measurement. This objectively measures how closely a light source matches natural light across the visible spectrum, averaging the differences of the spectral peaks and valleys between a light source and a standardised natural light source of the same CCT.  

Promising developments in light source technology.