Quote: Go by their behavior ..nerve racking at first but you'll soon learn when they are unhappy.
Having a thermometer in the brooder can be a good tool to augment your observations.
Substitute 'MHP' for 'lamp'...same theory applies...tho sometimes with the MHP you have to shove them underneath and hold them there until they 'feel the heat'.
The best indicator of heat levels is to watch their behavior:
If they are huddled/piled up right under the lamp and cheeping very loudly, they are too cold.
If they are spread out on the absolute edges of the brooder as far from the lamp as possible, panting and/or cheeping very loudly, they are too hot.
If they sleep around the edge of the lamp calmly just next to each other and spend time running all around the brooder they are juuuust right!
The lamp is best at one end of the brooder with food/water at the other cooler end of the brooder, so they can get away from the heat or be under it as needed.