diff --git a/js/cards/disk2.ts b/js/cards/disk2.ts
index 81398cf..be81b4e 100644
--- a/js/cards/disk2.ts
+++ b/js/cards/disk2.ts
@@ -145,10 +145,10 @@ const PHASE_DELTA = [
     [1, -2, -1, 0]
 ] as const;
 
-const DRIVE_NUMBERS = [1, 2] as const;
-type DriveNumber = MemberOf<typeof DRIVE_NUMBERS>;
+export const DRIVE_NUMBERS = [1, 2] as const;
+export type DriveNumber = MemberOf<typeof DRIVE_NUMBERS>;
 
-interface Callbacks {
+export interface Callbacks {
     driveLight: (drive: DriveNumber, on: boolean) => void;
     dirty: (drive: DriveNumber, dirty: boolean) => void;
     label: (drive: DriveNumber, name: string) => void;
diff --git a/js/ui/drive_lights.js b/js/ui/drive_lights.js
deleted file mode 100644
index ae0ce0f..0000000
--- a/js/ui/drive_lights.js
+++ /dev/null
@@ -1,20 +0,0 @@
-export default function DriveLights()
-{
-    return {
-        driveLight: function(drive, on) {
-            var disk = document.querySelector('#disk' + drive);
-            disk.style.backgroundImage =
-                on ? 'url(css/red-on-16.png)' :
-                    'url(css/red-off-16.png)';
-        },
-        dirty: function() {
-            // document.querySelector('#disksave' + drive).disabled = !dirty;
-        },
-        label: function(drive, label) {
-            if (label) {
-                document.querySelector('#disk-label' + drive).innerText = label;
-            }
-            return document.querySelector('#disk-label' + drive).innerText;
-        }
-    };
-}
diff --git a/js/ui/drive_lights.ts b/js/ui/drive_lights.ts
new file mode 100644
index 0000000..424fd0f
--- /dev/null
+++ b/js/ui/drive_lights.ts
@@ -0,0 +1,24 @@
+import { Callbacks, DriveNumber } from '../cards/disk2';
+
+export default class DriveLights implements Callbacks {
+    public driveLight(drive: DriveNumber, on: boolean) {
+        const disk =
+            document.querySelector('#disk' + drive)! as HTMLElement;
+        disk.style.backgroundImage =
+            on ? 'url(css/red-on-16.png)' :
+                'url(css/red-off-16.png)';
+    }
+
+    public dirty() {
+        // document.querySelector('#disksave' + drive).disabled = !dirty;
+    }
+
+    public label(drive: DriveNumber, label: string) {
+        const labelElement =
+            document.querySelector('#disk-label' + drive)! as HTMLElement;
+        if (label) {
+            labelElement.innerText = label;
+        }
+        return labelElement.innerText;
+    }
+}