Experiments
3.1. LED solar simulator
Four color LED are used, namely, red-R at 632 nm
(LTL2F3VEKNT), green-G at 525 nm, TOL-50bUGdCTa-M4), blue-B
at 468 nm (TOL-50aUBdCEa-ETB6) and white-W (LTW-2S3D7. Five
LED arrays, each at 227.5 mm 227.5 mm, are constructed and
serve as light sources of simulators, namely (Fig. 3),
(a) Four single-color LED arrays. Each array consisting of 1024 LEDs
has 64 parallel strings, each string has 16 LEDs in series with
a current limiting resistor.
(b) One combined RGB array. It has 1024 LEDs. The array has 128
parallel strings, each string has 8 LEDs. Percentages of irradiance
from red, green and blue LEDs to total irradiance are 35%,
33% and 32%, respectively.
Each LED array is placed 3 mm above a glass diffuser which is
30 mm over the test plane. LED heat sinks and forced air cooling
(between heat sinks and a glass diffuser) provide heat removal and
maintain a constant temperature heat sink temperature of 25 C. On