The answer to this question can be found in chapter 10; however, the text doesn't explicitly tell readers how Ralph feels about Piggy's suggestion. Throughout the story, Ralph has been placing all of his hopes for rescue into a fire. He believes it is likely the one that thing will draw attention to the island to bring help. Interestingly, Ralph ends up being correct when Jack lights an enormous fire trying to kill Ralph. The main problem with Ralph's current fire is that it can't be seen as well as the previous fire's location.

“It was different when the fire was—”

“—up there.”

The main goal of the current fire is smoke. Ralph hopes that it will produce enough smoke to be seen. That presents the problem of fueling the fire, and Ralph's group simply doesn't have the man power to tend the fire and search for fuel.

The fire was dying on them. “Two to mind the fire,” said Ralph, half to himself, “that’s twelve hours a day.”

“We can’t get any more wood, Ralph—”

“—not in the dark—”

“—not at night—”

Piggy's suggestion is to let the fire die down at night because the smoke can't be seen at night anyway. Ralph knows that Piggy is correct, and he reluctantly agrees to the suggestion. He isn't thrilled about not keeping his signal burning at night, but he also realizes that Piggy is right, and Ralph doesn't have a better solution.

Ralph stood up, feeling curiously defenseless with the darkness pressing in.

In Chapter 10, Piggy suggests that they let the fire go out at night and relight it every morning because he concludes that the smoke will not be visible at night. At this point, Ralph is frustrated that Jack has started his own tribe. Ralph is also discouraged that only he and Piggy seem intent on keeping the fire going. Upon hearing Piggy's suggestion, Ralph agrees to let the fire go out. However, Ralph thinks it would be ideal to have the fire going all the time. The fire also gives Ralph a sense of security, especially at night: 

Ralph stood up, feeling curiously defenseless with the darkness pressing in. 

Piggy suggest that they let the signal fire go out at night and relight it every morning. Why? How does Ralph react?

Thsi incident occurs in Chapter 10 of the novel, and it is after Jack has effectively seized power of the boys, and Ralph is left with Sam and Eric and Piggy, and they are trying to keep a signal fire going on the beach themselves. However, they face a number of problems. Firstly, there are only 4 of them, and Piggy with his asthma is not able to help collecting wood. Secondly, all the wood they can find is wet and rotten, which means that to keep the signal fire going involves constant attention and a constant search for more timber, which is more than they can do. Sam and Eric are clearly exhausted and they protest that they are unable to find any more wood, especially at night.

Piggy therefore suggests that they light the fire every morning, because, as he says, "Nobody ain't going to see smoke in the dark." Ralph's reaction to this is one of acceptance. Although he wishes for a fire for comfort at night, he agrees with Piggy and the twins: "Ralph stood up, feeling curiously defenseless with the darkness pressing in." Arguably, this feeling that Ralph has could be considered a foreshadowing of the attack of Jack and his tribe when they seize Piggy's glasses - and very significantly, they completely ignore the conch.