Solar Projector
Kenta Yamamoto

Kotaro Omomo

University of Tsukuba
kenta.yam@digitalnature.slis.tsukuba.ac.jp

University of Tsukuba
okkotaro@digitalnature.slis.tsukuba.ac.jp

Kazuki Takazawa

Yoichi Ochiai

University of Tsukuba
k.takazawa@digitalnature.slis.tsukuba.ac.jp

University of Tsukuba
Pixie Dust Technologies, Inc.
wizard@slis.tsukuba.ac.jp

Figure 1: Left: As an example of application, we show how projection was performed on plants. Right: Projection setup. It
consists of a mirror that reflects sunlight for the first time, a lens for condensing light, and a projector.

CCS CONCEPTS• Hardware → Displays and imagers;

KEYWORDS
projector, sunlight
ACM Reference Format:
Kenta Yamamoto, Kotaro Omomo, Kazuki Takazawa, and Yoichi Ochiai.
2018. Solar Projector. In Proceedings of SIGGRAPH ’18 Posters. ACM, New
York, NY, USA, 2 pages. https://doi.org/10.1145/3230744.3230767

1INTRODUCTION

The sun is the most universal, powerful and familiar energy available on the planet. Every organism and plant has evolved over theyears, corresponding to the energy brought by the sun. Humanity isno exception. We have invented many artificial lights since Edison
invented light bulbs. In recent years, LEDs are one of the mostrepresentative examples. Displays and projectors using LEDs arestill being actively developed. However, it is difficult to reproduce
ideal light with high brightness and wide wavelength like sunlight.
Furthermore, considering low energy sustainability and environmental contamination in the manufacturing process, artificial light
can not surpass the sunlight. Against this backdrop, projects thatSIGGRAPH ’18 Posters, August 12-16, 2018, Vancouver, BC, Canada© 2018 Copyright held by the owner/author(s).
This is the author’s version of the work. It is posted here for your personal use. Notfor redistribution. The definitive Version of Record was published in Proceedings ofSIGGRAPH ’18 Posters, https://doi.org/10.1145/3230744.3230767.

utilize sunlight have been actively carried out in the world. Concentrating Solar Power (CSP) generate electricity using the heatof sunlight to turn turbines [Müller-Steinhagen and Trieb 2004].
[Koizumi 2017] is an aerial image presentation system using thesun as a light source. Digital sundials use the shadow of sunlight toinform digital time [Scharstein et al. 1996]. These projects attempt
to use the direct sunlight without any conversion and minimize theenergy loss.
In this paper, we propose an image projection system using sunlight
as a light source (Fig. 1). Specifically, Digital Mirror Device (DMD)reflects concentrated sunlight and projects images with naturallight. In this way, it became possible to project images using lightin a wide wavelength range that can not be reproduced by LEDs.
By directly utilizing sunlight, it is possible to realize new projection
harmonious with nature, such as applying it to photosynthesis ofplants.

2IMPLEMENTATION

We propose a projector that uses sunlight as a light source andmakes the projected contents variable with DMD (Fig. 2). First ofall, in order to use sunlight as a light source, it is necessary to converge the sunlight into the optical path. The reason why sunlight iscondensed is that if it is tried to use sunlight without condensing,the optical circuit must be enlarged in order to collect necessaryenergy. If it is necessary to enlarge the optical circuit in proportion
to the necessary amount of light, the scalability as a projector is lost.

SIGGRAPH ’18 Posters, August 12-16, 2018, Vancouver, BC, CanadaK. Yamamoto et. al.

(a)(b)

Fresnel Lens
ScreenCollimating Lens

Focus
FocusedSun Light

MirrorSun
Light
Fly EyeLens

Projector

MirrorTIR

DMD

Figure 2: (a) Examples of the projection of three kinds of images. (b) Detailed view of the optical circuit. The figure on the leftof (b) shows how the light is focused on the projector part. The figure on the right of (b) shows how the collected sunlightpasses through the projector.

3Fresnel lensProjector

In Fig. 2, we show how three projected images are projected on
the screen using this projector. 8 bit grayscale image is projected
at 100 fps using DMD. Sony α7RII was used as a camera. The ISO
sensitivity was fixed at 100, the shutter speed was set to 1/125 s, andthe F value was fixed at 16. Moreover, the state of the sun during
shooting was clear and the ambient light was also bright enough.

4Figure 3: An application using sunlight in the house.

By concentrating, it is sufficient to scale only the light condensing
unit in accordance with the light quantity. Therefore, sunlight isreflected by a mirror and made incident on a Fresnel lens, so thatlight is focused.
Next, an optical circuit for suitably hitting the incident light to theDMD is described. The condensed light passes through the collimating lens and is homogenized with a fly’s eye lens. Total Internal
Reflection Prism (TIR Prism) is used to simultaneously irradiate theDMD and secure the optical path to the projection circuit. Finally,the screen is placed in a position so as to be parallel to the projectionlens so that the state of projection can be ascertained.

DISPLAY RESULTDISCUSSION

Since this projector is only a prototype, there are several aspects
that we would like to improve. Firstly, as we use sunlight, we needto implement a function that keeps converging according to themovement of the sun if it is to be used for a long time. Next, since theamount of heat becomes extremely high at the time of condensation,
the amount of light to be collected must be within the range of thethermal durability of the lens. In the future, our system can be used
for lighting utilizing sunlight in the house (Fig. 3).

REFERENCES
Naoya Koizumi. 2017. Sunny Day Display: Mid-air Image Formed by Solar Light. In
Proceedings of the 2017 ACM International Conference on Interactive Surfaces andSpaces. ACM, 126–131.
Hans Müller-Steinhagen and Franz Trieb. 2004. Concentrating solar power. A reviewof the technology. Ingenia Inform QR Acad Eng 18 (2004), 43–50.
Hans Scharstein, Werner Krotz-Vogel, and Daniel Scharstein. 1996. Digital sundial.
(Dec. 31 1996). US Patent 5,590,093.