What are the advantages and disadvantages of using photometric data files for lighting calculations?

These data can help select fixtures based on beam spread and light level data. They can also help determine if controls may be necessary in all vertical markets. It satisfies questions of the use of dimming, controlled circuit wiring and density of the subject light fixture(s)

An accurate representation of predicted light levels is of the utmost importance. In many cases this is a matter of occupant safety. That being said a calculation is only as good as your data. Reflectance and mechanical interference can turn a great lighting design into a legal liability. Always remember to account for these types of factor as a dark wall or a busy ceiling space where indirect lighting is used can create massive problems. Sometimes these problems can be addressed by selecting the ideal distribution or relocating lights to avoid potential issues.

Photometric data files are based on measurements, more specifically 'a measurement' and provide a snapshot of light output at various angles. But it's not a real snapshot, i.e. measurement of all angles at the exact same moment, it is like a 'panorama photo', a set of measurements collected in one file. Why is this important? This sequential measurement process introduces irregularities. Output (cd) varies over time because of temperature, positional influences, randomness, noise up to a few percent at least. You can observe this because a C-gamma coordinate system used in LDT and some IES files, the coordinate at gamma 0 degrees defines the exact same point in space for every C-plane, yet in many files they have different values.

This couldn't be more useful and important when layered lighting is specified. Static performance relates to tasks, such as in a commercial kitchen where bright lighting with good color rendering is critical. However, the dining areas may include a traditional seating area, a bar/lounge area and perhaps even private dining/events. It's critical not just to follow the theme in terms of aesthetics, but know the application of the space. Know too all of the requirements of the space; a young couple's light levels in private dining may be significantly different than patrons celebrating a 50th Anniversary in that same space.

In the case of accent lighting, correct selection can make the difference between achieving the intended effect and not. In this case, it is important to observe the calculated result and see if the desired light level contrast is achieved to highlight a subject or the correct optical control gives the intended effect. IES has good recommendations on the necessary light level delta to achieve the desired effect.

Very true! Start off at the specification sheet of the luminaire. Look for application data first. Perform a cursory layout just based on the application data. Then, from there, once you have an idea of the general coverage and lumen level of the selections, run those by your client. If they make selections based on your preliminary date, then drill down with the IES files and get the point-by-points done to confirm your initial findings.

This is getting off the intended subject but relevant while specifying - It is always a good idea to be mindful of the availability, it can paint more of a picture than you realize. Unless a light is for a very specific purpose (theatrical comes to mind), IES files should always be easily available for general illumination luminaires. IES files are expensive to generate and a manufacturer who allocates the necessary resources for IES files is more likely to possess the necessary resources to stand behind their product when something goes wrong. If IES files are not readily available or require my contacting the manufacturer for a non-custom product, I am unlikely to trust it.

The accuracy mentioned above, but also the different file formats are not a real problem. EulumdatTools is software I wrote to convert between IES and LDT, but also to verify these file formats using rules. There are many ways in which these file can contain inaccuracies: Specifying a complex symmetry while providing only one C-plane of data (making them rotation symmetric), missing light source data, insufficient number of measurement planes, etc. manufacturers should no just supply data but also ensure the correctness and usability for specifiers.

Also think about the space you are trying to light, the effects you wish to have. Indoor or outdoor, stray light from all sources. Reflective light from set pieces, or unintended surfaces, like wardrobes, or mobile presentation articles. Get as much information on the event as early as possible. Have a plan for adjustments on the fly. Accept that at a specific point in the day, you may have no control over an intrusive aspect that may throw off the look you are going for. If outdoors, test for you lighting as it goes through the day, into night, and how intense you need to keep things or bring the wattage down as the competition for stray light mitigation decreases. Many factors you must think of, and backups plans to make.

This is just wrong: it's not a disadvantage because the data should be best case allowing the designer to select the appropriate maintenance factors etc. If the file does not match the delivered luminaire then it's a Quality/Warranty issue. If you need a different alignment then you adjust your use of the file accordingly.

This is very important not to overlook! Also, be cautious of lighting engineers need to use "close proximities" because their IES files may be limited to specific chromaticity and consequential lumen outputs. It's important to ask of their conclusions are based on the IES data which used 4000K versus the 2700K you wanted to use in your site.

A portion of these assumptions are wrapped up in selecting an appropriate light loss factor. Reputable manufacturers are on approximately equal in manufacturing and should be approximately equal in lumen degredation, be weary of the manufacturer who suggests their LLF should be higher than their competitors. Be even more weary of manufacturers who suggest using an LLF above 1 unless you're in extremely cold conditions. Use the same LLF for all lights (of equal quality) and know that a driver is likely to fail well before lumen maintenance brings the light to end of life.

It is of the utmost importance that lighting designers get a chance to observe spaces they have designed. It's easy to read these lessons but they aren't going to sink in until you see a space that didn't turn out as you thought it would. Make mistakes, learn lessons and do better next time. Failure is always an option, failure is the birthplace of development.

Nothing is substantive in lighting unless it's peer reviewed. Like medical or product research, you need to verify the delivered results much the same as those studies. Also, consider the source!

In order to be able to validate and verify a lighting design the data files used should also be validated and verified. GIGO applies to lighting design as well so photometric data files should indeed be more thoroughly validated. My software EulumdatTools is designed for just that purpose.

Availability and Replacement The data can help with problems in the sourcing of the best replacement for multiple markets. Along with updating, upgrading or augmenting of house and touring plots for a specific reason. Ie arena show to stadium, live show to broadcast or adding more area to a house stage.

Simulating lighting design using software is not 100% science as physics, circumstances and noise will make any calculation result an approximation at best. A realistic looking image is not the same thing as accurate predictions of the actual performance.