Trong chân không, một ánh sáng có bước sóng <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-mstyle" id="MJXp-Span-2"><span class="MJXp-mn" id="MJXp-Span-3">0</span><span class="MJXp-mo" id="MJXp-Span-4" style="margin-left: 0em; margin-right: 0.222em;">,</span><span class="MJXp-mn" id="MJXp-Span-5">6</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-6">μ</span><span class="MJXp-mi MJXp-italic" id="MJXp-Span-7">m</span></span></span></span><script type="math/tex" id="MathJax-Element-1">\large 0,6 \mu m</script>. Năng l