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What is a Photometric Analysis?
And why do I need it?
Photometric analysis is the study of how light emanates from electrical lighting fixtures known as luminaires into the space being lit. At its core, the study provides a multidimensional simulation of a proposed lighting design, allowing clients and users to see the impact of the new plan. Ironically, the greater flexibility provided by LED lighting, which is on target to eliminate virtually all other forms of outdoor and indoor lighting by the middle of the next decade, is making it more important to perform photometric analysis before committing to new o replacement lighting plans. The differences in LED light direction, intensity and color make light for light replacement schemes more difficult than many realize. This note is designed to make electrical contractors and architects aware of the value of a professional photometric analysis and to highlight some of the pitfalls that can be very expensive when the analysis task is not done.
Although it’s not required for users to understand how the photometric diagram in Figure 1 is used, it is useful to know the basic physical properties of light it conveys to the designer.
Lumens (lm) is the total amount of light produced by a source regardless of direction.
Luminous Intensity, measured in Candela (cd), is the amount of light perceived or produced in a specific direction and is often referred to as the property of brightness.
Illuminance, measured in footcandles (fc), is often mistaken for brightness. It is the amount of light falling on a surface. It is affected by the luminous intensity of the source, the distance from the source to the surface, and the angle at which the light strikes the surface.
Figure 2 shows the simulated result of illumination with several of this type of downward driving luminaires in a sports center parking lot. Note how easy it is to see bright and dark areas and to get a comprehensive grasp for the overall effectiveness of the lighting design before a single luminaire has been purchased or an electrician has scaled a pole
Where is an Analysis Useful?
Photometric Analysis is especially useful in larger lighting projects because it allows all of the project stakeholders such as clients, city authorities and user groups to ask questions and come to agreement before work starts. Common projects where photometric analysis i usually done include:
When is an Analysis Important?
Some of the most important considerations for commissioning an analysis are financial and aesthetic needs such as:
Under What Circumstances is it Especially Important?
One of the most common outdoor lighting jobs performed today is the wholesale replacement of sodium and halogen lights with LED lighting in large area parking lots. The driving force behind this type of contract is lower owner running costs due to a combination of dramatically reduced power consumption, and reduced maintenance from longer bulb life. However, a parking lot LED lighting upgrade is a great example that showcases why it’s wise to perform photometric analysis at the quotation phase before replacing a single bulb.
Let’s say the parking lot’s 250W HPS lights are to be replaced with LEDs. At first glance it seems simple enough to replace the sodium lights with their watt to lumen equivalents. Armed with the efficacy specifications for each bulb type, it’s possible to figure out an equivalent LED light output and proceed with a lamp for lamp replacement.
However, the quality of the end result may not meet client expectations and the first time they’ll know is when they switch the lights on.
The reason for failure seems obvious but is all too common. It’s fair to assume the existing lighting space was designed with the characteristics of the HPS luminaires in mind, not the LED, meaning the only LED equivalent that’s obvious is likely going to be the light output just calculated. The designer needs to consider beam angle and beam spread; the angle the light emanates from the new bulb and the distance to the 50% intensity point of the illumination respectively.
These numbers help to calculate the number of bulbs needed to cover a given area which is likely not going to be the same number as the original HPS light plan. A photometric analysis allows ‘what if’ questions to be asked and answered by changing luminaires and lighting heights and locations in the simulation. Clients are able to work with contractors at the simulation phase making is much more likely all parties will agree on the implemented result.
What Information do I Need to Provide?
A photometric analysis is a computer simulation, so very often the only thing you need to provide to get one done is a city map or an architect’s drawing showing details of the space to be lit. Once the dimensions of the outside space are captured, key physical characteristics like walls, landscaping, stairs and pedestrian path routes can be added. It’s then a matter of adding locations and heights of light poles, wall packs and other luminaires.
Very often lighting clients know the type of luminaire they want to use. Our lighting experts can take photometric diagrams of those lamps and run the analysis to see if all of the aims of the lighting plan are being achieved. The best lamp for the job may not be the original choice, making the photometric analysis an important sales tool in addition to its technical value.
What you Get With a Hyperikon Photometric Lighting Study?
- Rendering and photometric analysis focused on uniformity and efficiency.
- Complete estimate - along with all the specs and extras you need to purchase.
- Installation maps and layouts - clearly showcasing locations, beam angles and foot-candles.
- Review of your current lighting layout.
- IES and photometrics - complete with charts and graphs to easily use for lighting from any manufacturer.