opengl – Some faces of mesh are exhibiting a lot darker than they need to be

Hey,

My site visitors mild mannequin has some darkish faces and I can not seem to perceive why?

I’m utilizing OpenGL.

That is my fragment shader:

#model 330 core
out vec4 FragColor;

in vec2 texCoord;

uniform sampler2D texture;

in vec3 colour;

in vec3 regular;

in vec3 fragPos;

uniform vec3 lightColor;
uniform vec3 lightPos;
uniform vec3 viewPos;

void principal()
{
    float ambientStrength = 0.8;
    float specularStrength = 0.2;

    float fixed = 1.0f;
    float linearr = 0.09;
    float quadratic = 0.032;

    float distance    = size(lightPos - fragPos);
    float attenuation = 1.0 / (fixed + linearr * distance + 
                    quadratic * (distance * distance));  

    vec3 ambient = lightColor * ambientStrength;

    vec3 norm = normalize(regular);
    vec3 lightDir = normalize(lightPos - fragPos);  

    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = diff * lightColor;

    vec3 viewDir = normalize(viewPos - fragPos);
    vec3 reflectDir = replicate(-lightDir, norm); 

    float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
    vec3 specular = specularStrength * spec * lightColor;   

    diffuse *= attenuation;
    specular *= attenuation;

    vec3 outcome = (ambient + diffuse + specular) * colour * texture(texture, texCoord).rgb;

    FragColor = vec4(outcome, 1.0);
}

I uploaded my site visitors mild mesh on GitHub right here:
https://github.com/hazh10/site visitors/blob/principal/trafficlight2.obj

Can somebody clarify why this occurs as a result of this does not occur to any of the opposite meshes?