**3. Materials and Methods**

(LED = light-emitting diode, HPS = high-pressure sodium lamp, FL = fluorescent light).

#### **3. Materials and Methods** *3.1. Experimental Design*

*3.1. Experimental Design* To investigate biomass yields and contents of volatile organic compounds (VOCs) of *Thymus vulgaris* L. grown under a broad-spectrum LED system, and to compare the lights' productivity as well as electrical efficiency with conventionally used lighting fixtures for the cultivation of thyme under naturally low irradiated greenhouse conditions during fall and winter in Berlin, Germany, a one-factorial experiment with a randomized block design with three different supplemental light sources and four spatially independent rep-To investigate biomass yields and contents of volatile organic compounds (VOCs) of *Thymus vulgaris* L. grown under a broad-spectrum LED system, and to compare the lights' productivity as well as electrical efficiency with conventionally used lighting fixtures for the cultivation of thyme under naturally low irradiated greenhouse conditions during fall and winter in Berlin, Germany, a one-factorial experiment with a randomized block design with three different supplemental light sources and four spatially independent replications (N = 384; *n* = 32 thyme plants per replication) was conducted.

Three different supplemental light sources ((1) fan-cooled light-emitting diode (LED)

frames 1.40 m above greenhouse benches, resulting in distances between the bottom of the LED, HPS, and FL light sources and the greenhouse benches of 1.14, 1.13, and 1.09 m, respectively. Based on weather recordings from WetterKontor [62], plants were exposed to an average of 2.5 h of sunshine per day during the experiment. In addition to the natural sunlight, plants were subject to supplemental lighting from 6:00 a.m. to 8:00 p.m. for a photoperiod of 14 h per day during the greenhouse experiment. Plastic sheeting extending from above the light fixtures to below the greenhouse benches eliminated neighboring

Irradiance measurements of the light fixtures were taken prior to the experiment using a spectral PAR meter (PG200N, UPRtek, Aachen, Germany) at night. Light intensity, spectral composition, and irradiance profiles (light distribution patterns) were measured and recorded at bench level under experimental conditions. The software package of the

), and (3) fluorescent lamps (FL) (VENEDIG, Pracht®

, Berlin, Germany, dimensioning 47.5 × 21.5 × 19.5

)) were horizontally mounted onto given steel

, Berlin, Germany, di-

, Berlin,

1SL, PHILIPS, Hamburg, Germany; ballast: HST, SILL Leuchten®

*3.2. Lighting Systems and Illumination Conditions*

(SUNtec Technology, FUTURELED®

Germany, dimensioning 50 × 50 × 16 cm<sup>3</sup>

mensioning 50 × 30 × 19 cm<sup>3</sup>

*3.3. Irradiance Profile Measurements*

light pollution.

cm<sup>3</sup>

lications (N = 384; n = 32 thyme plants per replication) was conducted.
