A Focus on Good Optics

Stockholm Lighting Interviews Dave Grassi

Lumenpulse stands out as a luminaire manufacturer with a dedicated optical team and many of their products use optics developed in house. We interviewed David Grassi, who leads this team in Montreal, to understand why.

Stockholm Lighting:  Would you mind introducing yourself and your team?

Dave Grassi: My name is David Grassi, I'm the Optical Engineering Manager at Lumenpulse, I have been at Lumenpulse for over 10 years and have been designing optical systems for LED applications for the past 14 years. 

At Lumenpulse, we have a team of 3 Optical designers, each dedicated and experienced in their segment (Lumenpulse Outdoor, Site and Area, and Point source). Their names are Isabelle Rivard, Caroline Donkin, and Gabrielle Grondin, each of them has also been working at Lumenpulse for over 10 years.

SL:  How common is it that lighting manufacturers have a dedicated team for this? Why does Lumenpulse find it valuable?

DG: Many lighting manufacturers will have at least one employee that is specialized in evaluating optical options found "off-the-shelf" and performing photometric testing, but having a dedicated team for optical design is indeed rare. By having this capability in house, we are able to design optical solutions and deliver truly best in class optical performances, ones that can't be easily matched simply by combining off-the-shelf solutions. Central to our company's DNA is customization of our product; we design all of our standard products with the intent that they can be customized further than any product on the market in terms of possible optical distributions and spectral power distributions.

Can you describe the process you use to evaluate and select optics for your products? How often are these re-evaluated?

For any new products, we first evaluate the market need and review what's currently considered "best in class"; we evaluate pretty much every option, the CCT offerings, the CRI, the outputs, the beam angles, and the intensity. 

For the beam distributions themselves, there is a lot more that goes into this than just hitting a certain beam angle number. The delivered intensity is calculated and optimized to ensure that we are efficiently directing all of the light within the desired distribution, this mitigates glare and stray light and ensures that you will get the highest light levels for your selected configuration. 

The shape of the distribution is critical as well, for narrow beams, we want to get every last photon within the beam angle to maximize the possible throw. For grazing distributions, we want to ensure that we are doing everything we can to mitigate shadows between fixtures, to allow for the widest possible spacing between fixtures to reduce project costs. For floodlighting and general illumination, we want to ensure efficient delivered output within the distribution but want to ensure that this doesn't lead to scalloping in the application. For site and area lighting, we want to ensure the furthest possible spacing between luminaires while maximizing the average illuminance on the roadway and minimizing backlight. We are constantly re-evaluating the performance of all of our products to see where we can continue to improve and innovate.

SL:  Now that LEDs are so efficient, raw output no longer seems to the main priority. What are priorities you have when designing optics for Lumenpulse fittings?

DG: LED products have been bright enough to be used in almost every application for years now, the efficiency of LEDs continues to improve every year, but this mostly translates into more and more output which is directly contributing to the continually increasing light pollution of our planet. Our priorities have been to focus more on delivering the right amount of light directly to where it's needed. 

We design our optics to ensure a very wide range of distributions to cover all applications and we specifically design these distributions to make sure that we don't have any gaps in the offering. If you take our Lumenbeam family for example, when you start with our narrowest beam angle and then go to the next wider option, the intensity will drop in half, this will continue across the entire range. The same goes for output as well, the Lumenbeam and Lumenquad family is the largest family of projects on the market today, going from as low as 15W up to 200W. 

This ensures that you should be able to find the right distribution for your application, one that delivers the appropriate amount of light in the best distribution possible to help designers realize their vision. 

DG: Just as critical as the performance metrics is the quality of light within each distribution in every product. When we talk about quality of light, this is also something that can be quantified. When we talk about quality of light and color consistency, this is often described in terms of steps. We see this a lot in our industry, that a fixture may be binned to 2 steps or even 1x2 steps, but this refers to the overall average color point of a luminaire being within a certain number of steps relative to the luminaire next to it. However, when we talk about a typical bare LED, there may be as many as 30 steps of color difference between the narrow angle light and the high angle light emitted from the LED. This is a function of modern LED manufacturing. 

When we add optics into the system, we are essentially imaging the LED, which would project this color difference into the beam itself, so it's our job as optical designers to correct for poor color over angle. We want to ensure that when we say our luminaires are binned to within 2 steps, we don't just mean that the average color point of Fixture A is within 2 steps of Fixture B, but that within a single fixture, there is no visible color difference in the beam nor field. We do a lot of work in the design and validation process to ensure that the end distribution is not just best in class performance in terms of output and delivered intensity, but that the quality of light meets the expectations of the market as well.

SL: Any tips for us folks out in the field? What should we consider when evaluating a luminaire?

DG: Don't just consider the spec sheets. Lumenpulse has nearly every single photometric file available on our website, including with accessories, which is a huge differentiator for us. Many projects will use accessories like snoots, visors, honeycomb louvers, and frosted lenses to reduce glare and skyglow, our database of photometric performance allows designers and specifiers to accurately model them in the space, because you can't just apply a LLF (light loss factor) to accurately represent how performance changes when adding these accessories. All of our performances are validated by 3rd party testing, which is our commitment to integrity. Having this information is a requirement for a lot of high profile projects, and we want to make sure that our partners can feel confident that what we say and what we show is backed up by hard data.

SL:  Any exciting news you want to share?

DG: Keep an eye on our website, we launched the brand new Lumenfacade Max this past fall, which showcases our in-house optical design expertise. We have a LOT of new products launching this year, with brand new and never before seen optical designs. We are really pushing the boundaries of performance across all of our products! 

Dave Grassi
Optical Engineering Manager, Lumenpulse 


To see the original article: stockholmlighting.com/news

Editor's Notes: 

About Lumenpulse 

Founded in 2006, Lumenpulse designs, develops, manufactures, and sells a wide range of high performance and sustainable specification-grade LED lighting solutions for commercial, institutional and urban environments. Lumenpulse is a leading pure-play, specification-grade LED lighting solutions provider and has earned many awards, including several Product Innovation Awards (PIA), Next Generation Luminaires Design Awards, Red Dot Product Design Awards and LIGHTFAIR Innovation Award. Follow Lumenpulse onTwitter,Instagram, andLinkedIn. 

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