Why a field study and an office simulation can disagree
The core difference is where the light and the sleep are measured. In a field study, participants go about their normal lives and wear an actigraph — a wrist device that records movement to estimate sleep and activity — for several consecutive days, so the light exposure recorded is whatever they actually encountered [4]. In a controlled office simulation, the lighting itself is manipulated: one study modified the natural light spectrum in an experimental office using foil that filtered the light, then measured sleep by wrist actigraphy [2], and another compared two lighting conditions in a simulated office while measuring sleep duration with wrist-worn actigraphs [3].
That design difference changes what a sleep gain means. A field study can show that people who happen to get more daylight also tend to sleep longer, but it cannot easily separate daylight from everything else that differs between people and days. A simulation can hold the setting constant and change only the light, which makes the comparison cleaner — but the sleep it records is still measured by actigraphy in participants living their normal lives outside the office [3].
What the field evidence actually shows
The field evidence points in a consistent direction: more natural light exposure is associated with longer sleep. In a field study of healthy older adults who wore an actigraph for five consecutive days, participants were significantly longer exposed to daylight, and the results confirmed this pattern [4]. An office-worker study combining actigraphy, surveys, and computer simulation of annual daylight levels in each participant's office reported that working in daylit office spaces appeared to lead to higher sleep [1].
The scope matters here. The older-adult study measured five days of real-life exposure and sleep [4], and the office-worker study used simulation only to estimate the annual daylight levels in each person's office rather than to control the lighting itself [1]. So these findings describe associations between naturally occurring daylight and sleep in ordinary settings, not the effect of installing a specific optimized lighting system.
What controlled office simulations add
Simulations contribute the piece field studies lack: a deliberate change in lighting. One study compared two lighting conditions in a controlled office simulation and measured sleep duration with wrist-worn actigraphs alongside cognitive performance, linking optimized daylight and views to sleep outcomes [3]. Another modified the natural light spectrum in an experimental office by filtering it with foil and tracked sleep by wrist actigraphy together with melatonin, cortisol, and other markers [2].
These designs can attribute a sleep difference to the lighting manipulation more confidently than a field study can. But the estimates are tied to the specific conditions tested — a particular spectrum modification [2] or a particular pair of lighting conditions in a simulated office [3] — so the size of the gain depends on what was changed and for how long, and the actigraphy still records sleep in participants' everyday environments rather than under laboratory control.
How to read the gap between the two estimates
Put together, the two approaches are complementary rather than competing. Field actigraphy captures the daylight people actually receive across their real days and shows that more exposure tracks with longer sleep [1][4]. Controlled simulations show that when lighting is deliberately optimized, actigraph-measured sleep can improve [2][3]. A reasonable reading is that field studies estimate the gain available from real-world daylight as it naturally varies, while simulations estimate the gain from a specified lighting change — and the two numbers should not be treated as the same quantity.
What remains genuinely open is how large an optimized-lighting gain would be if it were installed and measured in the field over a full year, since the simulation evidence comes from specific experimental setups [2][3] and the field evidence comes from observational exposure patterns [1][4]. The direction of the effect is consistent across both designs; the magnitude is where the designs diverge.
Sources used in this answer
Impact of daylight exposure on health, well-being and sleep of office workers based on actigraphy, surveys, and computer simulation
An office-worker study combining actigraphy, surveys, and computer simulation of annual office daylight levels reported that working in daylit office spaces appeared to lead to higher sleep.
Daylight spectrum and intensity reduction and its impact on melatonin, cortisol, alpha-amylase, sleep parameters and sleepiness in humans
In an experimental office where the natural light spectrum was modified by foil filtering, sleep measured by wrist actigraphy and hormonal markers were affected by the altered daylight.
The impact of optimized daylight and views on the sleep duration and cognitive performance of office workers
In a controlled office simulation comparing two lighting conditions, optimized daylight and views were linked to sleep duration measured by wrist-worn actigraphy, alongside cognitive performance.
Exploring the impact of natural light exposure on sleep of healthy older adults: A field study
In a five-day field study of healthy older adults wearing actigraphs, participants were significantly longer exposed to daylight, and results confirmed an association with sleep.