A four-year-old was killed by a train at a level crossing because her 67-year-old grandmother could not see the dim warning lights as she approached in her car.
Emma Lifsey was travelling in her grandma's car when she was hit by a train at Beech Hill Crossing in Nottinghamshire, on 4 December.
The Rail Accident Investigation Branch said the red warning lights, known as wig-wags, were old and could not be seen against bright sun on a wet road.
Network Rail said lights at the crossing have since been replaced. Emma, from Haxey in North Lincolnshire, died in hospital the day after the crash. Her grandmother survived the 60mph collision.
She told the investigation she only noticed the lights and barriers when she was very close to the crossing.
A report from the Rail Accident Investigation Branch (RAIB) blasted Network Rail for failing to notice the discrepancy.
It states the weather was sunny at the time of the lunch-time collision but there had been rain showers earlier and the road surface was wet, leading to glare from the low winter sun.
The report went on: "The RAIB took the wig-wag units and arranged for testing in an optical laboratory.
"It was found that they were fitted with 36W lamps and an obsolete design of red lens unit.
"Their light output was measured to be well below the specification for lights of this type.
"Network Rail had no plans in place to replace the light units with brighter ones and had no process to identify that such replacement was necessary."
Speaking after the incident, Emma's parents, Mark and Zoe Lifsey, aged 40 and 38, said: "Emma meant the world to us. She was our much-loved daughter and a baby sister to her 11-year-old brother Jack.
"We are still trying to come to terms with the terrible incident and there are no words that can properly express how utterly distraught we are. "We would like to thank everyone for the many messages of sympathy and support we have received. As you can appreciate, this tragic incident has left us shocked and devastated."