brightd: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/brightd - from package: brightd

You may install the required package with command apt-get install {package}

Error in other languages:
brightd: bevel nie gevind nie
brightd: comandă negăsită
brightd: comando não encontrado
brightd: commande introuvable
brightd: command not found
brightd: käsku ei ole
brightd: không tìm thấy lệnh
brightd: komanda nerasta
brightd: Kommando nicht gefunden.
brightd: kommandot finns inte
brightd: komut yok
brightd: nie znaleziono polecenia
brightd: níor aimsíodh an t-ordú
brightd: no se encontró la orden
brightd: no s'ha trobat l'ordre
brightd: opdracht niet gevonden
brightd: parancs nem található
brightd: perintah tidak ditemukan
brightd: príkaz nenájdený
brightd: příkaz nenalezen
brightd: команда не найдена
brightd: командата не е открита
brightd: 命令找不到
brightd: コマンドが見つかりません