Below I will discuss how I used my lighting and post processing to help guide the player through the environment. I'll also go over the puzzles and what the player has to do in order to succeed.
The hallway has two ceiling lights and a lit exit sign which immediately draws attention. This tells the player they'll probably have to go through that door. The fact the other doors won't open at first, also tells the player to move forward. The trap will then trigger and block the player's path. The doors behind them will then open.
The left room has a single ceiling light, as well as a wall light and a fallen lamp. The number pad also emits some light. The fallen light illuminates the four large marks on the closet; this is the first number for the code. The collectible on the bed and the key on the nightstand are left in the dark a little, so the player has to look close in order to find them. The ceiling light illuminates the number 3 on the middle bed, telling the player that is probably also a number they'll need; since it's the third number from the left (4 on the closet, 5 on the collectible) it would also be the third number in the code. The fourth number can be found on the number pad itself (there's a blood splatter on the 9, indicating it's been used before).
The right room also has a single ceiling light. The tubes, buttons and paint splatter emit light and there's a flickering blue light in the corner of the room as well. The tubes change color when the player presses the buttons and they'll have to change the tubes to the right colors; light blue for the far right one (because of the flickering light), purple for the middle one (paint splatter) and dark blue for the left one (blue pen scribbles on the collectible).
The number pad can be found on the desk. I've added minimalistic UI to the level to make things a little clearer in terms of controls.
The player has to type in the right numbers in order to lower the trap in the hallway. In a real version of the game this would be by pressing the buttons with mouse, but in my version it's by actually typing in the numbers on keyboard.
The collectible has a blood splatter in the left upper corner to pull the player's attention to it. There's a number 5 there, the second number of the code.
This collectible has blue pen on it. This is the color the corresponding tube has to be.
The tubes change color on button press. The right color combination will turn them all green and will make the spikes in the hallway disappear, if the other puzzle has been solved as well.
Below are some more screenshots of the level. Of course, all of this is also visible in the video, but I like to have these on display as well.