Basic Sustainable Lighting Concepts: On Daylighting

June 27, 2011 / no comments

Part 2 of an ongoing series outlining design principles for sustainable lighting design: here are a few ideas regarding daylighting, to help navigate the greenwash.

Only a little direct sun, please

Too much direct sunlight increases the indoor temperature, creating higher cooling loads. It also increases the potential for glare. If there’s too much glare, people are likely to pull the shades and leave them that way, which equals no more daylighting! Most interior shades do little to reject the heat load. Consider using exterior overhangs to keep excessive sun outside, and light-shelves to distribute the daylight indoors so it’s more useful.

Don’t add complexity and cost by creating one problem and mitigating it with another technology. The New York Times Building has been criticized for this. Its floor-to-ceiling glass has the potential to let too much light and heat inside, so the ceramic tubes outside the glass were introduced to help block some of it. If you have less glass to begin with, you can use less exterior shading… If you can afford it and don’t care, then have at it, as long as you keep your energy use down. Otherwise, try not to pile on unnecessary complexity chasing an aesthetic.

Installing shades is not daylighting

Simply installing internal glare-control shades or blinds is NOT a form of daylighting. Neither is using a lot of glass just to get more light inside. The façade of a building must engage the sunlight to utilize it in a meaningful way, coaxing the useful light in while controlling excessive light and rejecting heat. This means articulated façades, not flush glass.

If you do use shades, make them automated if you can afford it. Automated shades can adjust for different lighting conditions throughout the day, and they don’t rely on a forgetful occupant to pull them back up. If you can’t afford automated shades, try to design your envelope with external shades or a light-shelf such that you can keep the upper part of the window open all the time and still allow manual shading below it.

Dimming the lights

Daylight switching is no replacement for daylight dimming. Switching has a tendency to irritate occupants, because it flips the lights on and off throughout the day when the ambient light is near the threshold light level. More often than not, if it doesn’t work correctly, it will simply be disabled instead of fixed. You definitely can’t rely on people to make the best choices on an hourly basis either – the lights go on and stay on all day. Flipping a switch is what we’ve been trained to do all our lives.

Rely instead on dimming your perimeter spaces. There are variable levels of savings to be had here, from actual energy savings, to rebates just for putting daylight dimming systems in. Every little bit helps in terms of energy – initial cost is a different matter. There may be legislation or changes to the building codes in the near future that would require you to use daylight dimming anyway.

Digital is in!

All the ballast manufacturers, and a few lighting controls manufacturers, are finally, albeit slowly, switching over from older analog technologies, to digital or hybrid analog/digital systems that operate with greater precision and functionality. If you use one of these emerging technologies, your system is more likely to still be in style in the next decade or so (but don’t jump the gun on a brand-spanking-new product, lest it be discontinued). DALI is one of those technologies; it’s been around for about ten years now, and is slowly catching on in the US.

Don’t go crazy

Just because dimming is warranted in daylit zones and conference rooms, doesn’t mean you should use it everywhere. Some advocates claim additional energy savings by being able to dim the lights everywhere, but that would only be if you’ve over-illuminated your interior spaces to begin with. Design them correctly and you can save a lot of materials and costs. Dimming everything is another example of mitigating a problem that you may have created yourself.

Photo of the Month: October 2009

October 13, 2009 / no comments


It’s All Relative

Brightness, color, and contrast all play a role in any visual composition. This is especially true of lighted nighttime environments; the interplay of these three characteristics determines the quality and character of the lighted environment.

In the foreground of this image, on the right-hand side, is a brightly lighted mock-up of what is soon to be a prominent architectural feature of a new high-rise building under construction in Boston. The color-changing LED fixtures seen at the bottom of the image will highlight this building feature at different intervals, adding a playful element to the Boston skyline at night. The property owners will determine which colors to accent this element with, and therefore can control how subtle or dynamic this feature for different occasions. The use of color helps distinguish this lighted portion of the building from the sea of white light spilling from the windows of surrounding buildings in the skyline.

The overall brightness can be adjusted by dimming the LED fixtures. In the middle of the night, when most are asleep, the brightness can be reduced by dimming, giving a more subtle appearance than what might be desired earlier in the evening during prime viewing hours.

The contrast within a photograph taken shortly after dusk often produces the most striking images of lighted environments. The deep color of the sky enlivens the image, while it is the contrast between the sky glow and the dark silhouettes of buildings that defines the city skyline. A few minutes later in the day, and the sky will be too dark, the contrast is reduced, and the perception of the building forms is lost.

As designers we never want to use color or increase brightness just for the sake of doing so; more is not necessarily better. However, all of the lighted environments that we design must balance these characteristics – brightness, color, and contrast – and use them carefully to hopefully create architectural projects that become stunning images.

Photo Credit: Jamie Perry / Lam Partners Inc