The core mission of a solar simulator is to reproduce the spectrum, intensity, and spatial distribution of near real sunlight in the laboratory. Among them, the uniformity of light intensity directly determines the reliability of experimental data. Its development path is a history of evolution from traditional xenon lamps to advanced laser light sources, each step accompanied by technology and challenges.

Xenon lamp era: height compensation of optical systems

The short arc xenon lamp is a classic light source for simulators, and its spectrum matches the solar spectrum well. However, the xenon lamp itself is a high brightness point light source, and the difference in light intensity between the center and edge of its original spot is huge. In order to improve uniformity, the technological path relies on complex optical integration systems, such as integrators (optical rods) and compound eye lenses. These systems achieve uniform light intensity by splitting and superimposing light beams, breaking down and reassembling uneven light sources. The challenge of this path lies in its complex system, large volume, precise optical path calibration, and significant energy loss. The uniformity on the final illuminated surface is often difficult to break through the bottleneck of ± 2%.

Innovation of LED array: flexibility of electronic modulation

LED light sources achieve electronically adjustable spectra by integrating LED chips of different wavelengths into an array. In terms of uniformity, its advantage lies in the ability to actively "shape" the light field distribution at the light source level by accurately arranging the position of each LED in the array and independently controlling its driving current. This method is more flexible than passive optical correction. But the challenge lies in the fact that each LED still emits Lambertian light, with high requirements for mixing distance, and to avoid optical crosstalk between LEDs of different wavelengths, achieving high levels of uniformity still requires precise optical design and complex calibration algorithms.

Laser light source: potential challenges of the solution

Laser is a directional and monochromatic light source. In theory, by combining lasers of different wavelengths and scattering them with diffusion plates and vibrating mirrors, uniform light spots can be obtained. This path has enormous potential and is expected to achieve ultra-high performance. But the challenges it faces are also the most severe:

Speckle effect: The coherence of laser will produce severe interference speckle on the illuminated surface, disrupting uniformity. Eliminating speckle requires complex and expensive techniques such as rotating diffusion plates, acousto-optic modulators, etc.

Cost and safety: Multi wavelength laser systems are expensive, and high-power lasers pose significant safety hazards.

Conclusion: The path to improving the uniformity of solar simulator light intensity from xenon lamps to lasers is a process from relying on "post optical remediation" to "source light field design", and its core challenge has shifted from overcoming the non-uniformity of the light source itself to the higher-order problem of how to tame the relative dryness of the laser.