I am trying to build a night clock projector, inspired by this project: https://microengineer.eu/2018/05/01/diy-night-clock-projector/
As I am more a computer scientist than an electrical engineer, I prefer ready-to-use/plug-and-play solutions (I am not very good at soldering, and not at all at SMD soldering...).
The linked project recommend to use a small LCD screen with a power LED. But I had a hard time finding such LCD screen, compared to the cheap OLED alternative: https://www.buydisplay.com/serial-spi-i2c-white-0-42-inch-arduino-raspberry-pi-oled-display-72x40
However, this screen is advertised as 120 cd/m^2, and it doesn't seem enough to be projected to a ceiling 2 meters away (I did not manage to get anything projected, other than the activity LEDs of my RPi ^^')
In comparison, the LCD alternative (with pre-mounted backlight) is bigger and is advertised as 200 cd/m^2 (which is a rough average value for LCD). Finally I am not even sure that it is bright enough for clear projection.
Finally, I found this LCD screen (with no backlight) which is FAR more expensive, require a backlight (like this LED) and some soldering to connect all these things together. Here, it is hard to get some brightness comparison with other solutions.
What I come to is:
- 120 cd/m^2 times the size of the screen gives 0.008 cd for the pre-mounted OLED screen
- 200 cd/m^2 times the size of the screen gives 0.136 cd for the pre-mounted LCD screen
- 87 lm over 85 deg gives 30 cd for the LCD + LED
Is this comparison correct?
Is there a way to compute the required brightess/luminance/luminous flux/luminous intensity/illuminance for this kind of application?
Is there some "in-between" solution, with more than 0.136 cd but less than 30?