Can someone help me with a shorter code please?

Whenever you find yourself doing a repetitive task, remember that you can almost surely use loops (and/or functions) to make it go faster!

Here's the script with for loops:

local ison = false
script.Parent.CFrame = script.Parent.CFrame * CFrame.fromEulerAnglesXYZ(0, 0, 0)

local lightParent = script.Parent.Parent.Parent
function SetBrightness(brightness)
    for light = 1, 91 do
        for bulb = 1, 3 do
            local obj = lightParent["Light" .. light]["Bulb" .. (bulb == 3 and "" or bulb)]
            obj.PointLight.Brightness = brightness
        end
    end
end

function switch()
    if (ison == false) then
        ison = true
        script.Parent.CFrame = script.Parent.CFrame * CFrame.fromEulerAnglesXYZ(0, 2, 0)
        SetBrightness(15)
    else
        ison = false
        script.Parent.CFrame = script.Parent.CFrame * CFrame.fromEulerAnglesXYZ(0, -2, 0)
        SetBrightness(0)
    end
end

script.Parent.ClickDetector.MouseClick:connect(switch)

As you can see, a simple set of for loops can access all your objects without you have to type everything out.

Since you said you had 91 lights, each having 3 bulbs, we use two for loops. Next, note that game.Workspace.Something works just as well as game.Workspace["Something"], but sometimes we need to use the 2nd format if we want to include variables, numbers, or spaces. So, to access the proper Light model, we use lightParent["Light" .. light]. "Light" .. light appends the number 'light' to the string "Light"; ex, if we're on the first loop, light = 1, so this will give us model "Light1". The next part of the line does the same thing for the Bulb, but with an "inline if" (known as a Ternary Operator, see here ). Mainly, since you used the names "Bulb", "Bulb1", and "Bulb2", I told it that if "bulb == 3", don't append anything instead of appending the number.

I am guessing that you renamed everything for the sole purpose of identifying each one. For the future, this is not required. Instead of using a for loop, you can simply scan for models that have a specific name:

local ch = lightParent:GetChildren()
for i = 1, #ch do
    if ch[i].Name == "Light" then
        local lightCh = ch[i]:GetChildren()
        for j = 1, #lightCh do
            if lightCh[j].Name == "Bulb" then
                lightCh[j].PointLight.Brightness = brightness
            end
        end
    end
end

That bit of code goes through all models named Light and changes the brightness of all PointLights in bricks named "Bulb".

Since you've gone to the trouble of differentiating all the lights, I'd personally try adding a "wait()" command, for graphical effect (only looks good, I imagine, if you had a pattern you used while naming everything):

function SetBrightness(brightness)
    for light = 1, 91 do
        for bulb = 1, 3 do
            local obj = lightParent["Light" .. light]["Bulb" .. (bulb == 3 and "" or bulb)]
            obj.PointLight.Brightness = brightness
        end
        wait()
    end
end

(If you like the effect but want it to take longer, move the wait to the inner loop. If it takes too long, try "if light % 2 == 0 then wait() end", increasing the "2" to make it wait even less.)

What went wrong with your script? I'm guessing (since you didn't provide an error message) that you either have more than just "Light"s in script.Parent.Parent.Parent, or else your lights have more than just the 3 Bulbs in them (ie they probably have other "Part"s). Those other parts probably don't have PointLights in them, but your script didn't test for that -- it assumed that all children would have the PointLight.

that is annoying i'm sure haha. well all i can suggest are variables (local or global depending on what you need it for, but no point in making so many local variables) or tables (annex the code from the table using brackets [])