Commercial Daylighting

Commercial Daylighting

Having studied the engineering of daylighting for four years – it’s applications, model predictions, the techniques used, successful designs and analysis – I consider myself rather well versed in this form of engineering.  In fact, I wrote thousands of lines of codes that calculated the interaction of daylight in room surfaces using form factors and other advanced mathematics at the time.  That is why it pains me to write this article.  With the advancement of PV’s (DC generating solar panels) and wind turbines (i.e. on-site electrical producing devices) and the advent of LED lamps, daylighting concerns may become a thing of the past.  The engineering devices used in daylighting (light shelves, monitors, specially engineered fenestration) are expensive.  And, despite some of the greatest efforts, it is still difficult to get light to the interior of a building without adding heat.  This is a rather ironic result considering that commercial buildings are rarely heated – they are cooled the majority of their existence due to latent and sensible heat loads.  Thus, the dilema.  Spend thousands of dollars on daylighting features such as glazing, light shelves, “skytubes”, etc. (when in the right hands, I might add, enhance the look of a commercial building) or limit gazing (i.e. heat gain) and use those dollars on PV & wind turbines and LED lamps.  Currently, with the incentives from the government and utilities, the winner is hands down the latter.  There are no incentives for daylighting – the technique is too difficult for most to do correctly and it is difficult to quantify the costs vs. the savings.  In conclusion (as my heart bleeds to type this) it is currently far more economical and straightforward to integrate electrical generation elements (wind & solar) and lighting controls into the architecture of a commercial building than daylighting elements.  However, daylightng elements should be used and considered because the impact on the architecture can be stunning when integrated correctly – and allow commercial buildings to turn off the lights.  A proper focus and engineering analysis can produce stunning ecotecture that is both beautiful and sustainable.

4 Responses to “Daylighting – Final Answer”

  1. Grant Grable says:

    Dear Author:

    I pains me to think that you did research and came up with so much misinformation. The fact is, ASHRAE 90.1-2007 as well as the future published ASHRAE 90.1-2010 say quite the opposite of your findings. Daylighting is the most cost effective and efficient solar option available on the market. The key is lighting controls and high visible light transmission with 100% diffusion glazing devices that maximize the amount of hours per day that you can shut off lights. Please don’t believe me, investigate it for yourself. Look up ASHRAE 90.1-2007 addendum D or the 2008 California Title 24 mandate that just made all 8,000 sq.ft. buildings with 15′ or higher ceilings utilize proper daylighting. Even the U.S. Department of Energy published their findings on commercial building Toplighting (daylighting with controls) and found that by using the above mentioned, in all climate zones, their is a huge potential for daylighting that outways even opportunities with solar. Oh, and by the way, EPACT 2005 was amended in January 2008 to include daylighting with controls to be a renewable energy technology and eligible for the same tax incentives and Treasury rebate programs. There are cost effective solutions that are installed around the world with payback opportunities that pay for themselves in less than 3 years in many markets. Products with gimmicks don’t work. Tubular units cost to much and you can put out a fire with a garden hose. Properly designed, If you maximize the aperture of the skylights (not an expensive clear story or light shelf) and use the highest visible light transmission with 100% diffusion to eliminate hot spots or glare and add lighting control, you will not only reduce light energy substantially but it has been proven that you actually can cut your light heat load in half, saving A/C use in the process.

    High performance daylighting IS the most cost effect, renewable energy, solar option for the majority of building owners. Just ask Walmart, they have installed high performance prismatic skylights and lighting controls in over 2,400 properties with 200,000 sq. ft. of space each. Their connected light load is 1.2 watts per square foot. By their own calculations, One 30 square foot skylight shuts off 1.2 kW of light energy for 2,800 hours per year. Based on the NREL data on PV, that is the equivalent energy reduction of the annual output of 2 KW of PV panels (1,440 kWh per year per KW – NREL DATA). 2 KW of panels is approximately 360 square feet. This means that for a fraction of the cost and a fraction of the square footage, high performance daylighting outperforms PV all the time. There is no comparison.

    Again, don’t take my word for it, please check it out. The U.S. DOE Commercial Building Alliance Report on Toplighting for energy efficiency can be downloaded at:

    This report tells a lot in Section 4.6 and Section 5.2. Read for yourself. DAYLIGHTING SAVES AND IS FAR MORE VALUABLE THAN PRESENTED.

  2. Greg Terch says:

    First of all Grant, I love the passion you possess for daylighting. I welcome these types of debates over renewable energy sources – especially those dealing with lighting. I used to dream of integrating daylighting features into my own architecture when I studied illumination engineering at CU. I believed that daylighting techniques could enhance the exterior architecture and save thousands of watts of electricity. However, at the time, I had no idea what things cost to build and how clients actually used commercial spaces. The installation of 15′ ceilings in commercial buildings is rare and costly – things I learned from being a GC for 12 years. This is my dilemma – is it better to install high ceilings, large curtain walls and skylights in buildings that require a tremendous amount of materials to create proper daylighting or is it better to install standard ceiling heights, limited glazing with high insulation in opaque walls? The money saved by using the latter construction techniques could be put into PV and wind generation systems – this construction method makes more sense to me.

    As you know and referenced in the literature you provided, daylighitng takes high ceilings, certain ceiling to floor relationships and highly reflective surfaces. The other major problem daylighting faces is the need for large, open office environments – no walls or offices. Unfortunately, the majority of office buildings are sectioned into offices. The only daylighting technique for office spaces is then skylights. These are difficult systems to engineer due to the interaction of light with the room surfaces – i.e. the calculation of lumen levels on the work surface and the lumen level of each surface. The designer must understand form factors – the relationship between room surfaces and how they are going to interact with each other upon the introduction of the skylight. It is very difficult to control glare (harsh light from above) and create a comfortable illuminated environment. Other problems that are inherent with skylights – where to place electrical lighting since the center of the room is a skylight, creating a watertight seal between the aperture and the roof, cloudy environments limit the effectiveness, and again heat loss and gain (there inherently has to be increased heat transfer from a skylight with an R-value of 2.0 versus an opaque ceiling with a possible R-value of 50).

    I cannot argue your assertion of Walmart and their installation of skylights. They have the perfect architecture to accommodate skylights – single story structure, high ceilings, open architecture, highly reflective surfaces (white ceiling, white floor) and form factor relationships that create even lighting. But again, my argument is that daylighting does not work for all achitecture. My argument is to assess the design criteria correctly and choose daylighting, electric generation or a combination of both. Furthermore, I think you must take into account the evolution of electric lighting. The LED lamp is an amazing leap forward in artificial illumination – the electricity required to run them is nominal compared to other lamps and they last 60,000 hours. The advacement in artificial lighting is exponential and we should include that into our decision making.

    In conclusion, I don’t disagree with daylighting techniques for appropriate architecture. However, I don’t agree with installing high ceilings throughout a multi-story building and creating special floor to ceiling relationships that increase the effectiveness of daylighting but cost a fortune to construct. The high ceilings require large amounts of low insulating glass, light shelves, etc. to produce the required lumen levels at the areas furthest from the fenestration. Furthermore, skylights are not even part of the equation on a multi-story building – the 30th floor may work great but the other 29 floors are unaffected. However, the other 29 floors lighting energy requirements can be greatly enhanced by LED lamps and PV/wind power generation. So, I will reiterate what I posted – daylighting elements should be considered and implemented when possible. However, architecture should not be altered just for the sake of daylighting – make sure an in-depth analysis is conducted and then install the most cost effective and eco-friendly system for today and the future.

  3. Grant Grable says:


    I agree with your assessment. Cost effective daylighting does not work in multi-story buildings or deep plenum spaces where wells are needed to be created. The cost to construct each foot of depth increases the pay back while the depth itself causes the light levels needed to diminish. However, as the U.S. DOE research proves, even in low rise buildings with open ceiling plans, less than 5% of all the buildings that should be daylit have been and the energy efficiency opportunity in these buildings through daylighting properly is substantial. The issue comes back to design. Multi-story buildings are limited to vertical glazings and their integration with lighting controls is still an opportunity for energy efficiency as we will never get rid of windows (we tried that in the 1970′s and it failed miserably!) in industrial buildings. However, in low rise buildings with open or short plenum space, daylighting opportunities are very cost effective to do right!

    The biggest issue I have is the rush to implement Renewable Energy products into buildings that are energy hogs! If America was just to look at a mandate on lighting to get rid of high bay HID’s alone, especially in conditioned space, the energy savings and carbon impact would be immense. Yet, to this day, we are putting solar panels on roofs with stimulus money to buildings that are highly inefficient in the fist place.

    Daylighting is a passion of mine and my daily work. There is substantial opportunity in daylighting spaces properly with quick ROI opportunities. However, as you did outline, NOT in high rise applications!

  4. Greg Terch says:

    Grant, it has been great discussing the issues at hand with you. I wish you the best of luck in advancing the field of daylighting.

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