In summary, although actigraphy is not as accurate as PSG for determining some sleep measurements, studies are in general agreement that actigraphy, with its ability to record continuously for long time periods, is more reliable than sleep logs which rely on the patients' recall of how many times they woke up or how long they slept during the night and is more reliable than observations which only capture short time periods. Actigraphy can provide information obtainable in no other practical way. It can also have a role in the medical care of patients with sleep disorders. However, it should not be held to the same expectations as polysomnography. Actigraphy is one-dimensional, whereas polysomnography comprises at least 3 distinct types of data (EEG, EOG, EMG), which jointly determine whether a person is asleep or awake. It is therefore doubtful whether actigraphic data will ever be informationally equivalent to the PSG, although progress on hardware and data processing software is continuously being made. Although the 1995 practice parameters paper determined that actigraphy was not appropriate for the diagnosis of sleep disorders, more recent studies suggest that for some disorders, actigraphy may be more practical than PSG. While actigraphy is still not appropriate for the diagnosis of sleep disordered breathing or of periodic limb movements in sleep, it is highly appropriate for examining the sleep variability (i.e., night-to-night variability) in patients with insomnia. Actigraphy is also appropriate for the assessment of and stability of treatment effects of anything from hypnotic drugs to light treatment to CPAP, particularly if assessments are done before and after the start of treatment. A recent independent review of the actigraphy literature by Sadeh and Acebo reached many of these same conclusions. Some of the research studies failed to find relationships between sleep measures and health-related symptoms. The interpretation of these data is also not clear-cut. Is it that the actigraph is not reliable enough to the access the relationship between sleep changes and quality of life measures, or, is it that, in fact, there is no relationship between sleep in that population and quality of life measures? Other studies of sleep disordered breathing, where actigraphy was not used and was not an outcome measure also failed to find any relationship with quality of life. Is it then the actigraph that is not reliable or that the associations just do not exist? The one area where actigraphy can be used for clinical diagnosis is in the evaluation of circadian rhythm disorders. Actigraphy has been shown to be very good for identifying rhythms. Results of actigraphic recordings correlate well with measurements of melatonin and of core body temperature rhythms. Activity records also show sleep disturbance when sleep is attempted at an unfavorable phase of the circadian cycle. Actigraphy therefore would be particularly good for aiding in the diagnosis of delayed or advanced sleep phase syndrome, non-24-hour-sleep syn...

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The authors measured ambient illumination exposure in healthy volunteers in San Diego, California (latitude 32 degrees 43' N, n = 30), and Rochester, Minnesota (latitude 44 degrees 1' N, n = 24), during each of the four quarters of the year, which were centered on the solstices and equinoxes. Subjects wore photosensors on their wrists and lapels (or foreheads while in bed) 24 h per day for an average of 5-6 days per quarter. The maximum of the two illumination readings was stored each minute. Annual average time spent per day in outdoor illumination (> or = 1000 lux) was significantly higher in San Diego than it was in Rochester (p < .04). Daily durations of illumination at or exceeding thresholds of 1, 10, 100, 1000, and 10,000 lux were highly seasonal in the sample as a whole (p < .01 at 1 lux, p < .0001 at other thresholds). Seasonal variation in outdoor illumination was far more pronounced in Rochester than it was in San Diego (interaction p < .001) but remained significant in San Diego (p < or = .03). Seasonal variation in indoor illumination was generally similar in the two cities. The median Rochester subject experienced illumination > or = 1000 lux for 2 h 23 min per day during summer and 23 min per day during winter. The corresponding times in San Diego were 2 h 10 min and 1 h 20 min. Neither age nor gender predicted illumination duration at any level. Both season and geographic location strongly influenced human illumination exposure, and behavior (choice of indoor vs. outdoor environment) was the most important mediating factor.