我怎样才能使表格中的文本居中，以便 pdf 中的信息更接近？

Question

我已经在文档中编写了下表，但是每列之间有太多空间。

我想减少水平空间，这样看起来会更美观。就像这个例子一样。

我的代码如下，欢迎提出任何建议。

\begin{table}[ht]
        \centering
        \caption{ Radiometric and photometric units for light intensity characterization. Radiometric units describe the absolute radiant energy, whereas photometric describe brightness as perceived by the human eye. }
        \label{tbl:radiometri_photometric}
        \begin{center}
            
            \begin{tabular}{*{6}{p{.16\linewidth}}}
                \toprule
                \multicolumn{6}{c}{Radiometric} \\
                \toprule
                \multicolumn{2}{p{.33\linewidth}}{Symbol} & \multicolumn{2}{p{.33\linewidth}}{Quantity} & 
                \multicolumn{2}{p{.33\linewidth}}{Unit} \\
                \midrule
                \multicolumn{2}{l}{$\Phi_e$} & \multicolumn{2}{l}{Radiant flux} & \multicolumn{2}{l}{\si{\watt}} \\
                \multicolumn{2}{l}{$E_e$} & \multicolumn{2}{l}{Irradiance} & \multicolumn{2}{l}{\si{\watt\per\square\meter}} \\
                \multicolumn{2}{l}{$I_e$} & \multicolumn{2}{l}{Radiant intensity} & \multicolumn{2}{l}{\si{\watt\per\steradian}} \\
                \multicolumn{2}{l}{$L_e$} & \multicolumn{2}{l}{Radiance} & \multicolumn{2}{l}{\si{\watt\per(\square\meter\cdot\steradian)}} \\
                \bottomrule
                \\
                %\toprule
                \multicolumn{6}{c}{Photometric} \\
                %\toprule
                %\multicolumn{3}{p{.49\linewidth}}{School} & \multicolumn{3}{p{.49\linewidth}}{State} & 
                %\multicolumn{2}{p{.33\linewidth}}{Unit} \\
                \midrule
                \multicolumn{2}{l}{$\Phi_v$} & \multicolumn{2}{l}{Luminous flux} & \multicolumn{2}{l}{Lumen (lm)=\si{\candela\cdot\steradian}} \\
                \multicolumn{2}{l}{$E_v$} & \multicolumn{2}{l}{Illuminance} & \multicolumn{2}{l}{Lux(lx)=\si{\candela\cdot\steradian\per\square\meter}} \\
                \multicolumn{2}{l}{$I_v$} & \multicolumn{2}{l}{Luminous intensity} & \multicolumn{2}{l}{Candela (cd) = \si{lm\per\steradian}} \\
                \multicolumn{2}{l}{$L_v$} & \multicolumn{2}{l}{Luminance} & \multicolumn{2}{l}{Nit (nt) = \si{\candela\per\square\meter}} \\
                \bottomrule
            \end{tabular}
        \end{center}
    \end{table}

Answer 1

\documentclass{article}
\usepackage{array}
\usepackage{caption}
\usepackage{booktabs}
\usepackage{siunitx}

\begin{document}


\begin{table}[ht]
\centering
\caption{ Radiometric and photometric units for light intensity characterization. Radiometric units describe the absolute radiant energy, whereas photometric describe brightness as perceived by the human eye. }
\label{tbl:radiometri_photometric}
\begin{tabular}{@{}lll@{}}
    \toprule
    \multicolumn{3}{c}{Radiometric} \\
    \midrule
    Symbol & Quantity & Unit \\
    \midrule
    $\Phi_e$ & Radiant flux & \si{\watt} \\
    $E_e$ & Irradiance & \si{\watt\per\square\meter} \\
    $I_e$ & Radiant intensity & \si{\watt\per\steradian} \\
    $L_e$ & Radiance & \si{\watt\per(\square\meter\cdot\steradian)} \\
    \midrule
    \multicolumn{3}{c}{Photometric} \\
    \midrule
    $\Phi_v$ & Luminous flux & Lumen (lm)=\si{\candela\cdot\steradian} \\
    $E_v$ & Illuminance & Lux(lx)=\si{\candela\cdot\steradian\per\square\meter} \\
    $I_v$ & Luminous intensity & Candela (cd) = \si{lm\per\steradian} \\
    $L_v$ & Luminance & Nit (nt) = \si{\candela\per\square\meter} \\
    \bottomrule
\end{tabular}
\end{table}


\end{document}