Depending on the type and level of play of your specific application, the required light intensity measurement will differ. Illuminance, also known as incident light or brightness, refers to the amount of light that hits a surface. The only way to be sure that proper light levels are available is to measure them. Calculated by the density of lumens per unit area, illuminance is a measure calculated at a surface (like the clay of a tennis court). The standard measures for illuminance are footcandles and lux.
Light should be measured on both the horizontal and vertical planes. The horizontal measurement is known as the horizontal illuminance and is the amount of light that lands on a horizontal surface, such as a tabletop. The vertical measurement is know as the vertical illuminance and is the amount of light that lands on a vertical surface, such as a wall. It is important to consider both vertical and horizontal illuminances in your lighting design.
How Is Illuminance Measured?
In the United States, horizontal and vertical illuminances are measured in footcandles; most other countries measure this luminous emittance in lux. Footcandles and lux are quite similar; one lux equals one lumen per square meter. If you have a lux light intensity measurement, simply divide it by 10.76 to solve for footcandles. Conversely, if you have a footcandle measurement, multiply it by 10.76 to solve for lux.
What Happens When Vertical Illuminance Is Not Factored Into a Design?
Measuring illuminance to achieve satisfactory results ensures minimal shadowing. Illuminance values for applications and lighting solutions typically depend on the complexity of the visual tasks being performed for the lighting setup. For instance, if a tennis court is illuminated from only one side or end of the court, it could very well have sufficient horizontal footcandles but may lack the desired vertical footcandles. Any person, piece of equipment, or even a tennis ball, would create a shadow and would seriously affect one’s ability to play. Measuring both horizontal and vertical illuminances will help even out the light and minimize shadowing.
Does Symmetrical Lighting Guarantee Sufficient Light Levels?
While it is unlikely that anybody would design lighting for a sports court or a facility from only one side, lighting specialists at Access Fixtures frequently get requests for this kind of design. If a sports court, driveway, stadium or other large outdoor area is illuminated with a symmetrical lighting arrangement, many tend to assume the vertical illuminance will be sufficient and balanced. Unfortunately, that is not always correct.
For instance, if a balanced and symmetrical lighting design causes light trespass near the property line, the fixtures causing that light trespass might have to be redirected, shielded, or replaced with lower-wattage units. The fixtures on the other side of the court, however, may be fine as they are. After making these adjustments, the design will no longer be symmetrical and its vertical illuminance will be far less even. There is even the possibility that the resulting vertical illuminance will be insufficient for that specific court or facility. Vertical illuminance must be measured in asymmetrical lighting designs.
Photometric Studies Predict Vertical and Horizontal Illuminance
Photometric studies, also known as photometric analyses, are the easiest way to calculate horizontal and vertical illuminance before a project is built. Photometric studies are computerized simulations of lighting plans. The results of a photometric study will predict the horizontal illuminance and vertical illuminance at multiple points of the area being simulated. To order a photometric analysis, click here.
Speak to an Access Fixtures Lighting Specialist about Vertical and Horizontal Illuminances
Are you in the market for a new fixture? Not sure how many lumens your space needs? Call the lighting specialists at Access Fixtures today! We want to make sure you get the exact fixture for your needs, your budget, and your goals. We are passionate about lighting and love what we do—we’ll get you an answer. Contact us at 800-468-9925.