The aim of this randomized controlled trial was to examine the effect of an improved environment on sleep, anxiety, and depression in patients undergoing open heart surgery. This study aims to answer the following main questions:

• According to Watson's Human Care Theory, what is the effect of the improved environment on patients' sleep level and sleep quality?
• According to Watson's Human Care Theory, what is the effect of the improved environment on patients' anxiety and depression levels?

In order to observe the effect of the improved environment on sleep, anxiety, and depression, the researchers ensured that the room temperature, humidity, and lumen range of the light were at the appropriate level in the first 3 days after the surgery of the patients in the experimental group and gradually decreased them gradually.

The aim of this randomized controlled trial was to examine the effect of an improved environment on sleep, anxiety, and depression in patients undergoing open heart surgery. This study aims to answer the following main questions:

• According to Watson's Human Care Theory, what is the effect of the improved environment on patients' sleep level and sleep quality?
• According to Watson's Human Care Theory, what is the effect of the improved environment on patients' anxiety and depression levels? Before collecting data for this study, the "G. Power-3.1.9.2" program calculated the sample size at an 80% confidence level. The "Sample Calculation Formula with Known Universe (Population Volume)" (n = Nz2pq / d2(N-1) + z2pq) determined the sample. The literature review determined the "effect size" value to be 0.096. Taking the primary type error of 5% (Z = 1,96), the test power of 80%, and the effect size value of 0,096 units, we calculated the minimum sample size as n = 60. Therefore, the study included 60 volunteer patients, with 30 placed in the experimental group and 30 in the control group.

Data were collected using the Personal Information Form, the Richard-Campbell Sleep Questionnaire (RCSQ), and the Hospital Anxiety and Depression (HAD) Scale.

The patients who underwent open heart surgery and who were in the experimental group were admitted to the ward from the postoperative intensive care unit and the environment was improved for three days based on the improved environment of Watson's HCT, and on the morning of the fourth day in the clinic, the patients were interviewed face to face and the Personal Information Form, RSCQ and HAD Scale were completed. The following improvements were implemented within the scope of environmental improvement:

• Considering the seasonal conditions, the patient room was ensured to have appropriate temperature (18-26 °C) and humidity values (30-60%), and the temperature and humidity were gradually reduced and maintained in the appropriate range by monitoring at 21:00, 22:00, and 23:00 (Days 1, 2, and 3).
• In line with the environmental arrangements, the brightness of the light in the patient room was gradually reduced at 21:00, 22:00, and 23:00 using the Light Meter LM-3000 (Days 1, 2, and 3).

Characteristics of the measuring instrument and application

• The humidity and temperature of the patient room were measured with a Digital-Clock Humidity Meter and Thermometer Device. The Digital-Clock Humidity Meter and Thermometer is a digital thermo-hygrometer that displays indoor temperature and humidity values. The device can stand on the desktop or hang on the wall. The device displays temperature and humidity values, and it also stores the highest and lowest values in its memory. Temperature measurement units can be selected as 0°C or 0°F. The temperature measurement range is -10 to +600, and the accuracy is ± 1 °C. The humidity measurement range of the device with a temperature resolution of 0.1 °C is between 10 and 99%. The humidity sensitivity is ±5%, and the humidity resolution rate is 1%. The device's dimensions are (L) 102 x (W) 21 x (H) 110 mm. It weighed 122 grams.
• The luminous intensity of the light in the patient room was measured with the Light Meter LM-3000 mobile application provided by the researcher. Luminous intensity is the amount of luminous flux per unit area of a surface per unit time. E represents it, lux serves as its unit, and a luxmeter measures it. By definition, we divide the luminous flux of the surface by its area (E = lumen/m2). Light Meter LM-3000 is a mobile application that measures the illuminance of light in lux. Its measurement algorithm offers unrivaled precision to capture the slightest lighting changes, opening up new possibilities in light pollution and health research. Developed by optical scientists and engineers and compatible with five languages, the Light Meter LM-3000 is calibrated using professional Class A equipment for all iPhones and iPads.

The patients in the control group continued to receive standard treatment and care. On the morning of the fourth day after the patients were admitted to the ward from the postoperative intensive care unit, the patients were interviewed face-to-face and the Personal Information Form, RCSQ, and HAD Scale were completed.

Inclusion Criteria:

• Patients between the ages of 18 and 65 who have undergone open heart surgery and who are conscious and willing to communicate and cooperate.

Exclusion Criteria:

• Patients younger than 18 years and older than 65 years who did not want to participate in the study voluntarily

The datasets used to support the findings of this study are available from the corresponding author upon request.