field--node--field-fieldname.twig.html need some help

Hi,`

i´m using D8 and i need some help with my field--node--field-fieldname.twig.html
I want that my field is only shwon for logged in users, so i tested:

{{logged_in}} and {{is_admin}}

these variables are ever 1, so i think i do not get the right variables, or i can not use them.

I want to do it like this:

{% if 'Test' starts with 'T' %}

{% set field_name_class = field_name|clean_class %}
{%
  set classes = [
    'field',
    'field-' ~ entity_type|clean_class ~ '--' ~ field_name_class,
    'field-name-' ~ field_name_class,
    'field-type-' ~ field_type|clean_class,
    'field-label-' ~ label_display,
    'clearfix',
  ]
%}
{%
  set title_classes = [
    'field-label',
    label_display == 'inline' ? 'inline',
  ]
%}
<p>{{logged_in }}</p><p>{{is_admin}}</p> //everytime both are 1!!!

<div{{ attributes.addClass(classes) }}>
  {% if not label_hidden %}
    <h3{{ title_attributes.addClass(title_classes) }}>{{ label }}</h3>
  {% endif %}
  <ul{{ content_attributes.addClass('links', 'field-items','meinoverride') }}>
    {% for item in items %}
      <li{{ item.attributes }}>{{ item.content }}</li>
    {% endfor %}
  </ul>
</div>
{% endif %}

Thanks for helping me.