Not trying to start a fight here, but you seem somewhat fixated on darkness as the main issue. I never said SAR teams can't or don't ever work in the dark. I said it depends.

Caves present a certain range of hazards, which can be dealt with in darkness. Some environments have other dangers not generally present in caves, which can be tough to deal with in the dark.

As just one example, consider avalanche terrain. Skiing up a valley in the dark, when you can't clearly see what is above and below you, can be very risky. Are you skiing under a massive cornice? Are the slopes above you steep enough to slide? Are they freshly loaded? Are there signs of recent avalanche activity on nearby slopes of similar aspect? Are you traveling above an "terrain trap" where even a small slide will result in a deep, probably unsurvivable burial?

If I were in charge of a SAR team, with responsibility for the lives of my team, I would want carefully evaluate the whole situation, not just how good of headlamps we have.

There have been some such statistics gathered, but I don't have them. My recollection is being told that the NPS had found that the two largest causes of death and injury to SAR team members were driving to and from the incident, and aviation accidents. Note that this may be because nowadays SAR teams generally put a lot of emphasis on carefully evaluating risk before sending teams into hazardous situations. But driving we often just take for granted. Regarding aviation, in recent years most agencies (USCG, NPS, Alaska State Troopers, etc), have adopted formal, stringent, procedures for evaluating Risk/Reward for aircraft in SAR response. This is a result of a large number tragic aviation accidents that killed SAR team members. A friend of mine died, flying at night, on a mission that probably should never have been launched in the dark.

Come with me to the Dark Side, Luke...

I was reacting to the original statement in the training film which stated that the reason for not continuing the search was the coming of night. When I was active, night capable aircraft were a rarity, but ground teams could certainly have been dispatched. Our motto was "Search is an Emergency" and we had numerous examples to cite. I woud certainly agree that rescuers must be properly trained, equipped, and briefed on conditions surrounding the operation

I agree that many factors influence the decision to activate, and your example of avalanche terrain is a very good example - pay attention to the hazards (Avalanches are rarely a problem in southern Arizona - we would probably welcome the moisture). OTOH, the traditional alpine start, 2 AM or so, has traditionally been dictated by the likelihood of avalanche, cornice collapse, etc. being less likely in the wee morning hours, and highest in the afternoon.

We were pretty aggressive about responding to a search aggressively. Many times that immediate response was unnecessary, but from time to time, lives were definitely saved and delay would have incurred more suffering, if not fatalities.

In my experience, we did lose one member, a very fine person, who contracted Valley Fever while driving on dusty roads during a protracted training exercise, although it took several years before he succumbed. He and I both attended the only SAR related memorial service I have ever attended, one held for two AZ Highway Patrol helicopter pilots who crashed on their final mission, having just discharged several members of our group.

You must consider many factors in going into the field, but darkness is just one of them, and often not that important.