The most common and most likely answer to this crossword clue is the 5 letter word SMILE
S
M
I
L
E
Buddy explains!

The straight part
We know that "beam" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case beam = smile.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SMILE mean?
SMILE noun- A facial expression comprised by flexing the muscles of both ends of one's mouth, often showing the front teeth, without vocalisation, and in humans is a common involuntary or voluntary expression of happiness, pleasure, amusement or anxiety.
- Favour; propitious regard.
- A drink bought by one person for another.
- To have (a smile) on one's face.
- To express by smiling.
- To express amusement, pleasure, or love and kindness.
- To look cheerful and joyous; to have an appearance suited to excite joy.
- To be propitious or favourable; to countenance.