We know that light exerts pressure upon matter.
I'm imagining a hallway where an intense light source on one end shines towards the other end. The goal is to have the beam of light exert so much pressure that a human being cannot enter (or reach the end of) the hallway. Of course, we only want to deter the human, not to burn them to a crisp.
Would this be realistic?
No, it won't be realistic.
The radiation pressure produced by an electromagnetic radiation of intensity, or better irradiance, $I_f$ impinging at an angle $\alpha$ on a surface can be calculated according to
$P_{Inc} = \frac{I_f}{c} \cdot \left(\cos \alpha\right)^{2}$
where c is the speed of light.
You immediately see that, due to the c factor, you need huge irradiance to get meaningful pressures at human scale. Let's say you want to achieve $1 \ \frac{N}{m^{2}}$, you would need an irradiance of about $3 \cdot 10^8 \ \frac{W}{m^{2}}$. That would char any human on which it impinges.
In case of a person wearing a perfect reflecting suit,
if the wave is specularly reflected, then the recoil due to the reflected wave will further contribute to the radiation pressure. In the case of a perfect reflector, this pressure will be identical to the pressure caused by the incident wave
$P_{Inc}= 2 \frac{I_f}{c}$
It just halves the required radiance to achieve the same pressure, thus still leaving an extremely high value.
Not with light pressure. You need 300 megawatts of radiation flux for each Newton of force on the object (equivalent to the force exerted by a ~100 gram weight).
However, you can use microwaves as non-lethal deterrent. A moderate microwave flux is extremely painful on skin, well before it becomes damaging. This is the basis of several experimental crowd control weapons in real life, such as https://en.wikipedia.org/wiki/Active_Denial_System
No
It's true that light exerts a pressure, but photons have no rest mass and very little else (thanks AlexP). You're dealing with pressure created by a distribution of energy, which is miniscule.
If you think about it, your skin burns on a beach — but you don't feel even the slightest pressure from the light that's burning you.
Now increase the light such that you could feel the pressure. You'd flash into a fine ash before you could comprehend that you were feeling pressure.
But!
What if you change your goal just a bit? What if the original intent of the light was to flash-burn anyone trying to get down the hall? Your protagonish knows this and dresses accordingly in attire that protects he/she from the burning properties of the light. And yet, as he/she walks down the hall, feels the pressure! pressure that's great enough to hinder progress! That would be a cool twist to the story.
Literally , no. Other answers have dealt with this.
However, if you allow that the possible intruders will not be armored, you can do something like it.
Produce the light by an array of high-powered emitters. Each separate emitter produces a beam which focusses down to a very, very small spot about 1/4 to 1/10th the length of the hallway. The beams are all aimed at different spots within the hallway, and none of them is aimed directly down the corridor. As a result, virtually all of the emitted light will be absorbed by the walls.
The result will be hazardous to look at from the end of the hall, due to unavoidable (hopefully small) reflections. However, if you attempt to traverse the hall, you'll eventually encounter a wall of "hot spots", where the power density is so great as to burn holes in you. Before you get to that point, the perceived temperature will rise to unbearable levels, and this should keep intruders out.
Of course, this won't work in the presence of suitable armor - if the intruder simply rushes the corridor, she will pass almost instantly through the "death zone", and ought to be able to make it.
