Daylighting – Final Answer

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.

Daylighting – Get the Story Straight


Daylighting is the art & science of delivering visible solar light into a dwelling during daylight hours.  This is easy to do if one considers only the natural light gained and, therefore, the lights turned off during the day.  However, daylighting is a very delicate balance between light & heat gain/loss.  In order to gain natural light, we must provide fenestration.  The best windows on the market (without breaking the bank) may provide an R-value of 4.0.  The wall immediately adjancent that window can have an R-value of  40 with nearly normal construction methods.  So, for example, I design a house with large amounts of fenestration, place them without regard, and never turn on a light during the day – wonderful.  You were probably at work all day anyway.  However, the huge amount of glazing caused your A/C to run at full speed during the 100°F ambient temperature of the daytime.  This is not the intent of daylighting!  It is more eco-friendly to use no windows and LED lighting throughout the home than it is to convert the well insulated walls into glazing in the name of daylighting.  These are the types of the issues that frustrate me – people on soapboxes preaching about something they know nothing about.  Residential glazing should be used for two things.  First, provide us glimpes of the outside and bring nature inside.  Second, exchange heat as required – provide UV heat (passive solar heating) in the winter and convection cooling in the summer.  This requires shading of the window during the summer months when the sun is high and full penetration of the UV light in the winter when the sun is low.  However, these issues are aspects of passive solar heating & cooling – not daylighting.  Daylighting is a concept that must be discussed in the realm of commercial dwellings – the lights are on all day.  I will discuss daylighting concepts in my next posting – you need to know the difference between passive lighting & passive heating first.  In conclusion, understand that daylighting should be secondary to passive thermal controls in residential design.  We want to bring in large amounts of natural light but we also want to avoid large, negative effects placed on our HVAC systems.

Red Light, Green Light
May 17th, 2009

Red Light, Green Light

Compact Fluorescent

LED Lamp

With an M.S. in Illumination Engineering, I can’t help but get excited about advancements in lighting.  Since Edison created the first commerically practical lamp in 1879, the world has been illuminated by the incandescent bulb.  Although they are inexpensive and reliable, their time as our major light source is nearing an end.  The light source has two major problems:  it uses a significant amount of electricity and generates a significant amount of heat.  In fact, the light you are seeing is created by heating up a tungsten filament up to 3000°C!  That heat generated must now be offset by your HVAC system.  The new ‘buzz word’ in lighting is the Compact Fluorescent Lamp (CFL).  I will never forget seeing my first Compact Fluourescent (CFL) at a CU-Boulder reatreat in 1993.  It was the prototype of the new Greenfluorescent revolution.  Although the CFL is significantly more energy efficient, has a longer lamp life and a lower operating temperature, it is still fatally flawed.  First, the standard model off the shelf cannot be dimmed.  It requires a more costly, electronic ballast in order to be dimmed.  Second, the CFL is a disposable nightmare due to the Mercury contained inside the bulb.  Well, have no fear, the lighting future is upon us with the introduction of LED lamps for residential and commerical use.  LED‘s, or Light Emitting Diodes, have a bulb life of 60,ooo hours (6 times that of a CFL and 40 times that of incandescent) and use 70% less energy than a CFL (see Light Bulb Comparison Spreadsheet)!  Although these light sources are currently expensive, they can save you up to $674 a year by replacing your incandescent bulbs ($.23/kWh assumed in study).  In fact, when compared side-by-side with CFL’s, they pay for themselves in less than a year.  LED’s are the wave of the future and are truly the Green alternative when it comes to lighting!  Check them out today at EcoLEDs and reduce your carbon footprint.