Lighting: Still Cool as a Direct Response HVAC Strategy

Lighting: Still Cool as a Direct Response HVAC Strategy

This piece was originally published in the March 2018 issue of electroindustry

Scott Ziegenfus, Manager of Government and Industry Relations, Hubbell Lighting

In June 2012, electroindustry magazine published my article on “Integrating Light Control into Your Company’s Demand Response Strategy.” At the time, facility managers frequently disagreed about how lighting could be an equivalent partner to HVAC in load-shedding for demand response (DR) events.

The majority of facility managers considered HVAC the only option for DR because of the natural correlation with climate condition triggers. Lighting, on the other hand, was considered a steady event. Facilities would use the same light energy on a Tuesday in June as a Wednesday in November. Hence, facility managers naturally gravitated toward HVAC for DR.

My point was that lighting in an average commercial building was a larger part of the annual electricity used than HVAC. The 2003 U.S. Energy Information Administration (EIA) Commercial Buildings Energy Consumption Survey demonstrated that lighting accounted for 38 percent of the electricity used in commercial buildings. Ventilation, space heating, and cooling combined was a little more than 30 percent.

The argument was solid. Lighting was the single largest consumer of electricity in an average commercial building. A 2012 EIA survey,[1] however, showed lighting’s share in these same facilities had decreased more than 50 percent, from 38 percent to 17 percent.

In the nine years between studies, the introduction and enforcement of energy codes designed to reduce light power densities with the addition of more control technology significantly decreased lighting’s contribution to a commercial building’s electrical energy consumption. The lighting industry delivered on the promise of electrical energy savings far beyond other end-use contributors.

Now that LEDs have taken hold as the dominant light source with their low energy, long life, and high output capability, the electrical consumption of lighting might be at 15 percent or even lower. If that’s the case, is the contribution of lighting marginalized when it comes to DR? Does lighting even still have a role in DR? And if it does, what is it since it’s certainly not pure volume?

The answer is yes. Lighting may not be the dominant contributor but can be a significant complement by filling in the shortcomings of HVAC with its predictable, linear, responsive, and nonintrusive nature. An analogy is an old stereo amplifier; it had a knob for tuning and another for fine-tuning. The tuning knob would do the basic work of setting the sound. The fine-tuning would tweak for optimal performance. Lighting can be the facility’s fine-tuning DR knob.

Lighting Measures Up

Here’s how lighting is different than HVAC:


Unlike HVAC, lighting is shielded from many environmental influences. Daylight, or the contribution of the sun on room lighting, is the only environmental contribution that affects lighting. Daylight harvesting itself is predictable with the altitude and azimuth of the sun on any given day at any given orientation to a building. When you take into account that daylight harvesting affects only one of the multiple energy-saving strategies used in a building, the effect is minimal, if nonexistent. Predictability facilitates the ability to map how much electricity can be curtailed through lighting at any time during a normal business day.


Lighting is instantaneous to the human eye. The way HVAC deals with the thermal mass of a building is like a freight train. It starts slowly, but as it builds to a steady speed, inertia makes it difficult to stop. The same is true with the thermal mass and inertia in a building’s HVAC controls. It takes time to recover desired temperature after a DR event, and if the recovery is pushed too hard, a spike in energy use can occur. Lighting gives that fast and exact response desired by the facility team to react, tweak, and counter small mistakes or unforeseen changes from a DR event with HVAC.


Lighting is linear—if you add current, you increase light, and if you decrease current, you decrease light, proportionally. Controlling the thermal mass of a building is not a linear function. It takes time to reach a temperature setpoint, and then it fluctuates around it. The linear nature of lighting allows for precise control that equals a set amount of light. This level of precise controllability affords lighting the ability to counter any mistakes in a DR / peak demand minimization program or to make simple and quick tweaks any time of the day.

While predictability, linear operation, and responsiveness permit the facility team to work lighting easily into DR methodology, the nonintrusive nature of its cursory changes does not affect productivity. This comes from the human eye working increasing or decreasing its aperture like a camera. This function is automatic and unperceivable to the user but allows for a 15 percent or more decrease or increase in lighting to be unnoticed.

Studies by the Lighting Research Center at Rensselaer Polytechnic Institute[2] show that 80 percent of subjects accepted as normal up to a 30 or 40 percent reduction of light, and 50 percent could not detect a 15 or 20 percent reduction at all. This demonstrates that a facility can decrease or increase lighting to counter HVAC DR/PDM measures without a negative impact on tenant comfort.

The industry has done a terrific job in decreasing lighting’s energy use compared to HVAC in commercial buildings over the last 15 years. Its prominence in a DR strategy, however, has not diminished if it is used as a counter measure for DR events.



One thought on “Lighting: Still Cool as a Direct Response HVAC Strategy

  1. A well-articulated post with loads of details on lighting. The post deals with a subject that can help people to understand how to change the conventional ways of lighting to reduce energy consumption. Thanks for the post.

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