Understanding Light Intensity
Light is a fascinating thing. From the dual nature of light as a particle and wave, to the combination of colored light to make new colors, it is an illuminating element that we often take for granted in day-to-day life. When it comes to the clinical setting, different aspects of illumination become very important considerations. In this article, we’ll take a deep dive into one specific element of illumination: Light Intensity.
The first thing to know about light intensity is the language that surrounds the topic. Many have probably heard the term lumens (and some may have heard foot-candle), but in the modern world of surgical lighting “lux” is king. Lux is the International System of Units (SI) measure of illuminance and refers to the number of lumens per square meter. The area part of the equation is crucial in defining intensity. If you produce the same number of lumens (think amount of light) over a larger area, it will appear dimmer and less intense.
Intensity and area of illumination lead to one of the most crucial factors in rating a surgical light source: working distance. To start this discussion, we will use the analogy of a car headlight.
A car’s headlight emits the same amount of light all the time, but the farther away from the source you go, the more area the light inhabits, and the lower the intensity. Think about the driver of a car: the road directly in front of the car is very well illuminated, but farther down the road everything is still dark.
When it comes to surgical lighting, the same is true. An LED Headlight will appear much more intense at a close working distance than at a far one. If you were to put on a Surgical LED Headlight and shine it at a white wall your eyes would not feel very good two inches from the wall; It would get easier on the eyes as you moved away.
To exemplify this fact, we looked at Enova’s brightest LED Surgical Headlight: the Quantum Cool. The Quantum Cool has a maximum lux of 500,000 at a working distance of 10″ (25.4cm). Fourteen inches is an average working distance for typical surgeons.
To show how intensity decreases over distance from the source, we used a lux-meter to measure output at distances other than 14”. Below you will find the data showing the same effect as the car’s headlights. LED headlights appear much brighter the closer you are to the source.
What does this mean for surgeons and other headlight users? It means the intensity of light that you experience is directly related to the distance at which you work, not just the output of the headlight you use.
Enova Pro Tip
When trialing or purchasing new headlights, it is important to know what working distance(s) headlight manufacturers use to measure lux. Also, make sure to consider the working distance that is most comfortable for you. Your personal working distance can be easily measured by measuring the distance from the front of the headlight to your hands with elbows positioned at a 90° or your typical hand placement when working with patients.
We consider 10 – 14″ (25 – 36 cm) to be a standard working distance for measurement, but the industry has no defined standard, and some headlights are reported at 12″ or less. An LED headlight may say claim to have a lux of 125,000 at 14”, but if you work at 12” it will appear much brighter than that.