Study on Circadian Lighting in Hospitals

Study on Circadian Lighting in Hospitals




Guidance Document

This publication is sponsored by the Lighting Energy Alliance and Light and Health Alliance at the Lighting Research Center, at Rensselaer Polytechnic Institute. The Lighting Energy

Alliance is sponsored by Efficiency Vermont, Energize Connecticut, National Grid, National Resources Canada, the Northwest Energy Efficiency Alliance, and ComEd Energy

Efficiency Program. The Light and Health Alliance is sponsored by Armstrong Ceiling and Wall Solutions, Axis Lighting, CREE, GE Current a Daintree Company, Ledvance, OSRAM

and USAI Lighting.

Copyright © 2020 by Rensselaer Polytechnic Institute. All rights reserved. No part of this publication may be reproduced in any form, print, electronic or otherwise, without the

express permission of the Lighting Research Center.

This guide was written by Allison Thayer based on a study by Mariana Figueiro, Jennifer Brons, Charles Jarboe, and Allison Thayer. The author thanks David Pedler for his



There are two goals when specifying lighting for patient health and

energy savings in hospital rooms:

1. Establish a target circadian stimulus (CS) during the daytime to

promote improved sleep quality and psychological well-being in

hospital patients, potentially speeding recovery time.

a. Deliver a daytime CS of 0.3 at the eyes of a patients’ eyes.

b. Provide multilayered circadian-effective light in the morning

and circadian-ineffective light late in the day to maintain circadian

regulation and visual comfort for the patient.

2. While meeting visual and comfort requirements, maximize the

ratio of CS to lighting power density (LPD), measured in W ft-², andthus minimizing energy use.


• Providing high levels of CS can require more energy than is required to maintain recommended [1] ambient/general lighting in patient rooms (horizontal illuminance [EH] of 200 lx), but is roughly equivalent to the energy required to achieve recommended examination light levels (EH of 500 lx).

• The most effective lighting solutions for providing the target CS to a patient sitting upright while minimizing energy use were:

– Adding a supplemental overhead layer of narrowband short-wavelength (blue) light to the spaces’ general ambient lighting.

– Installing an array of at least two high-lumen, low-wattage 2×2 troffers to deliver an EH of 500 lx and a correlated color temperature (CCT) of 3000 K or higher.

• When designing lighting for a patient room, it is important to consider several options:

– Employ overhead luminaires with a vertical illuminance (EV) to EH (EV: EH) ratio of at least 0.75:1.

– Employ overhead luminaires with wide, diffuse distributions and high luminous efficacy.

– Avoid luminaires with printed images (e.g., nature scenes, clouds) on the lens as the primary light source in the patient room, as they have a very high power demand when configured to deliver sufficient light for circadian

stimulation.- If not using supplemental blue light, provide an average EH of 500 lx on the patient bed.

The recommendations in this document are based on the findings of a Lighting Research Center (LRC) study that investigated lighting design techniques for promoting health and well-being while minimizing energy use in hospital patient rooms.

Lighting for Health and Energy Savings in Hospitalized Patient Rooms – Guidance Document

Page 2


Hospitalized patients often experience heightened levels of depression, stress, and anxiety as well as poor sleep quality resulting from their respective health conditions and the nature of the hospital environment [2] [3] [4]

[5]. Electric lighting in hospitals often remains static throughout a typical 24-hour period and, especially in-patient rooms, delivers light levels that are too low for circadian stimulation during the day or too high for avoiding circadian disruption during the evening and night. These lighting conditions can severely disrupt sleep, as was found in a study [6] evaluating sleep quality among intensive care unit patients who showed a reduction of average sleep-time from a minimum normal duration of 8 hours to as little as 6 hours, with only 3 hours of that sleep occurring at night. Given that sleep quality is a key factor in health outcomes and recovery time, it is important for patients to achieve an adequate duration of consolidated sleep with low sleep-onset/offset latencies [7]. Recent research [8] has identified methods for using electric lighting to improve patient recovery by entraining their circadian rhythms to the natural 24-hour light-dark cycle, which can also improve sleep quality and psychological well-being while in the hospital.

A recent study [9] by the LRC at Rensselaer Polytechnic Institute and Mount

Sinai Hospital in New York City investigated circadian-effective light exposure

among hospitalized multiple myeloma (MM) patients. It was demonstrated

that providing a CS of 0.3 for up to 3 hours in the morning improved clinical

depression ratings compared to an experimental control condition providing a

CS of 0.1 during the same time interval. Nocturnal melatonin levels (a marker

of the circadian system) were maintained high in the intervention group while

it was significantly reduced in the control group, suggesting that the latter was

experiencing circadian disruption from staying weeks in the hospital.

The CS metric is derived from circadian light (CLA) which is irradiance at

the cornea weighted to reflect the spectral sensitivity of the human circadian

system. CS is defined as the percent nocturnal melatonin suppression achieved

after a one-hour light exposure from threshold (CS = 0.1) to saturation (CS =

0.7). A CS level of 0.3 or greater for at least two hours a day was also found to

be effective at improving sleep quality and reducing depression in people with

Alzheimer’s disease and related dementia living in long term care facilities. As

such, lighting for circadian entrainment is fast gaining interest among lighting

specifiers and manufacturers.

One drawback to this approach is that delivering high levels of circadian-effective

daytime light often requires more energy than is needed for general ambient

illumination or typical visual performance tasks (though it is equivalent to the

energy needed for patient examination). Delivering high levels of circadianeffective morning light may also overlap with the timing of peak energy demand

in the hospital . Therefore, the LRC recommends providing patients a minimum

of 2 hours of high CS exposure in the morning while minimizing energy

consumption by following the steps described in this document.

Circadian disruption is a common problem for hospital patients and can result in reduced sleep duration, which can delay recovery time.

Providing the recommended CS during the daytime can improve patients’ sleep quality and mood. The daytime light levels required for circadian entrainment (similar to those required for patient examination) are often higher than those recommended for general ambient lighting, and therefore have the potential to increase lighting power demand.

Lighting for Health and Energy Savings in Hospitalized Patient Rooms – Guidance Document Page 3


To facilitate circadian entrainment and patient recovery, the LRC recommends

providing CS ≥ 0.3 for at least 2 hours in the morning, CS ≤ 0.2 in the afternoon,

and CS ≤ 0.1 in the evening and nighttime.

The adjustable positions of patient beds (from fully reclined to sitting upright)

and patients’ gaze directions must be taken into account for considerations of

CS and discomfort glare. Since bed positions are variable, the LRC recommends

targeting a CS of 0.3 for the lowest amount of light from headwall or overhead

luminaires received at the eyes of patients in a fully upright position .

To ensure CS is being delivered while minimizing energy use, the LRC

recommends maximizing to the greatest extent possible the ratio of CS

to lighting power density (CS:LPD), measured in W ft-2. Though numerous

lighting products and configurations can be used to meet these performance

specifications, the Design Process section below points specifiers to products

and strategies that are most likely to maximize the CS:LPD ratio.

Further detailed specifications and methodologies for designing circadianeffective lighting for day-active people can be found in the recently published

UL Design Guideline 24480.

The chart below shows the CS:LPD performance of lighting configurations

using seven commercially-available overhead, footwall, and headwall luminaires

with two EH targets: (a) “general” (200 lux) and (b) “examination” (500 lx

on the patient bed). These lighting conditions were analyzed at six* CCTs

(2700, 3000, 3500, 4000, 5000, and 6500 K) with the bed in a 45° reclined

position and two patient gaze directions (45° above horizontal and directly

forward, parallel to the floor.) Also included are four combination designs using

a multifunction luminaire at 200 lx and 3500 K supplemented by a layer of blue

light from overhead recessed linear luminaires or footwall wallwashers.

Time of Day CS

Morning ≥ 0.3

Afternoon 0.2

Evening/Night ≤ 0.1

Design to reach CS targets for the patient in an upright position with gaze directly forward . Also consider the patient gazing upward at 45° above horizontal (when reclined) especially when evaluating the possibility of discomfort glare from overhead luminaires. Provide a CS ≥ 0.3 to the patient for at least 2 hours in the morning to promote circadian entrainment, and reduce CS for the remainder of the day to allow for recovery, rest, and sleep.

*An artificial “Skylight” luminaire was available with a combined CCT of 7000 K, whose SPD was only

included for this luminaire type in the analysis. The median LPD was derived from the entire set of LPD

values for each lighting condition evaluated for the study.

Designs should strive to be at least within the light gray zone in the chart to the right, which is ideal for reaching the daytime target CS of at least 0.3 while staying below ASHRAE guidelines for a

maximum LPD of 0.68 W ft-2.

Lighting for Health and Energy Savings in Hospitalized Patient Rooms – Guidance Document Page 4

Step 1 Model your space

The circadian-effectiveness of the overhead lighting is far less critical if supplemental blue light can

be used to provide high CS to patients. Some manufacturers may offer photometric simulation services, or provide assistance with the process upon request. Decide early in the design process if you can use an

additional layer of blue light to supplement the typical overhead lighting. Provide separate control for this layer in case of emergency and/or for better color discrimination during exams.

Design Process

Step 2A Decide if a Supplemental Layer of Blue Light Can be Used

Build a 3D computer model of the patient room in a photometric simulation program and arrange

vertical and horizontal illuminance calculation points

Use a photometric simulation model of the patient room to calculate EH on the

patient bed as well as EV at the eye. Arrange horizontal calculation points in a

6” × 6” grid on the bed, as well as vertical points along a line 4’-0” above finished

floor (AFF) pointed in the direction of the eye of a patient gazing upward at

45° above horizontal (reclined) and looking directly forward (upright). Using

the resulting vertical illuminance, together with the source’s spectral power

distribution (SPD), calculate CS using the web CS calculator developed by the

LRC: Take into account the height

of the bed, which may vary between manufacturers, when determining EH and EV

calculation point heights above the floor.

Consider a layer of narrowband, short-wavelength “blue” light to supplement

the typical overhead lighting. To achieve a CS of 0.3, 8 lx of blue light at the eye

(in addition to the multifunction troffer delivering an EH of 200 lx horizontal

at 3500 K) was needed for the patient in the upright position. By far, the

most effective means of delivering the supplemental blue light was from the

overhead recessed linear luminaires. The linear wallwashers on the footwall

were able to provide the additional blue light needed to reach a CS of 0.3 for

the patient in the reclined position, which was the only position in which the

footwall luminaires could reach the target CS of 0.3. However, the footwall

location required 10 times the energy compared to blue light provided by an

overhead source. Thus, while adding a supplemental layer of blue light can be

very effective, the location of the luminaires can significantly affect energy use

and efficiency. Reflecting blue light off the footwall required as much as 10 times more energy to

achieve the same amount of blue light to the eye of the patient compared to the

overhead luminaires.

Lighting for Health and Energy Savings in Hospitalized Patient Rooms – Guidance Document Page 5

Step 2B Design Overhead Lighting to Provide Adequate CS and Maximize CS:LPD

If additional layers of saturated blue light cannot be used, specify overhead luminaires with an

intensity distribution and CCT that will be most likely to provide a high CS for limited energy use

Look for overhead luminaires with an EV :EH ratio of at least0.75:1. Average EV :EH ratio of overhead luminaires for a patient with their gaze upward at 45° above horizontal, and looking forward.

Intensity Distribution

Design for the worst-case scenario in terms of patient position, but keep in mind the potential for discomfort glare from overhead luminaires when the patient is gazing upward.

Given the variability of the vertical angle of occupant gaze in this application,

the location of the luminaire plays an important role when designing to achieve

CS targets in an energy-efficient manner. The bar chart below shows the

percentage of lighting conditions (illuminance levels and CCTs) that reached a

CS of at least 0.3 from different luminaire locations, and for the patient looking

upward at 45° above horizontal, and looking forward.

In rare instance when the patient is lying flat and gazing at the ceiling, a

headwall luminaire with a direct lighting component will likely be the most

efficient means of delivering high CS with minimal energy use . In a more

realistic scenario with much less risk of discomfort glare, the patient will be

reclined at 45° with their gaze either angled upward at about the same angle

or directly forward. In this scenario, our analysis found that the direct/indirect

headwall luminaire achieved a CS of 0.3, but the CS:LPD ratio was the fourth

lowest of the conditions that achieved a CS ≥ 0.3 for this patient orientation.

With the patient upright, the number of headwall luminaire conditions

(distributions and CCTs) that provided a CS ≥ 0.3 was reduced to zero.

The circadian effectiveness of a light source is specified in terms of EV, or light

incident on an observer’s retinae, but current lighting standards are based on

EH, or light incident on the work plane. Luminaires with intensity distributions

that deliver higher EV:EH ratios also generally increase CS:LPD ratios and, thus,

improve energy efficiency.

To ensure higher CS:LPD ratios, it is necessary to evaluate the intensity

distributions and location of luminaires in the patient room using photometric

simulation software, favoring overhead luminaires that deliver a high EV:EH ratio

(i.e., at least 0.75:1) when the patient is looking forward. When the patient is

looking upward, the EV:EH ratio should be even higher. Conditions with CS ≥ 0.3

While providing high light levels for circadian entrainment is critical in hospital

patient rooms, it is also very important to avoid discomfort glare and provide

a comfortable and relaxing environment for the patient. Overhead luminaires

were the most effective at delivering high CS, but also have the highest

likelihood of being perceived as glaring, especially when the patient is in the

reclined position looking upward. This can be compensated for by keeping

light levels lower (EH of 200 lx) and using a high CCT (6500 K) or using

supplemental blue light from overhead. But, when light levels must be higher

(EH of 500 lx) either for CS or patient examination, also providing higher

levels (EH of 200 lx) of ambient illumination from additional luminaires in the

room (either on the footwall, or overhead throughout the rest of the space)

can keep discomfort glare to a more manageable level. Specifiers or designers

concerned about glare should use well-shielded luminaires or luminaires with

large-aperture, low-luminance lenses/diffusers, and reduce contrast between

the overhead lighting and the surroundings.

Design solutions that can achieve the target CS > 0.3 at varying bed positions and

patient gaze direction: (a) For a patient fully reclined, direct/indirect illumination from

a headwall luminaire; (b) For a patient fully reclined, overhead white light reaching

an EH of 200 lx; (c) For a patient reclined 45º with an upward gaze, overhead white

light reaching 500 lx horizontal (d) For a patient reclined at 45º with a forward gaze,

overhead white light reaching 500 lx horizontal. e) For a patient reclined 45º with a

forward gaze, combination of overhead ambient illumination (200 lx horizontal) with

saturated blue linear luminaires.

Web-based Calculator Link:

Light and Health Video Series

Sponsored by the Light and Health Alliance and the National Institute for

Occupational Safety and Health (NIOSH), the LRC has released a series of

short videos, with a total run time of just over 30 minutes.

YouTube Link:

Lighting for Health and Energy Savings in Hospitalized Patient Rooms – Guidance Document Page 10


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